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* [PATCH 0/6] keys: request_key() improvements(vspace)s
@ 2019-05-22 22:46 David Howells
  2019-05-22 22:46 ` [PATCH 1/6] keys: Fix request_key() lack of Link perm check on found key David Howells
                   ` (5 more replies)
  0 siblings, 6 replies; 7+ messages in thread
From: David Howells @ 2019-05-22 22:46 UTC (permalink / raw)
  To: keyrings; +Cc: dhowells, linux-afs, linux-security-module, linux-kernel


Here's a fix and some improvements for request_key() intended for the next
merge window:

 (1) Fix the lack of a Link permission check on a key found by request_key(),
     thereby enabling request_key() to link keys that don't grant this
     permission to the target keyring (which must still grant Write
     permission).

     Note that the key must be in the caller's keyrings already to be found.

 (2) Invalidate used request_key authentication keys rather than revoking
     them, so that they get cleaned up immediately rather than hanging around
     till the expiry time is passed.

 (3) Move the RCU locks outwards from the keyring search functions so that a
     request_key_rcu() can be provided.  This can be called in RCU mode, so it
     can't sleep and can't upcall - but it can be called from LOOKUP_RCU
     pathwalk mode.

 (4) Cache the latest positive result of request_key*() temporarily in
     task_struct so that filesystems that make a lot of request_key() calls
     during pathwalk can take advantage of it to avoid having to redo the
     searching.

     It is assumed that the key just found is unlikely to be superseded
     between steps in an RCU pathwalk.

     Note that the cleanup of the cache is done on TIF_NOTIFY_RESUME, just
     before userspace resumes, and on exit.

I've included, for illustration, two patches to the in-kernel AFS filesystem
to make them use this.

The patches can be found on the following branch:

	https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/log/?h=keys-request

and this depends on keys-misc.  Note that the AFS patches aren't on this branch.

David
---
David Howells (6):
      keys: Fix request_key() lack of Link perm check on found key
      keys: Invalidate used request_key authentication keys
      keys: Move the RCU locks outwards from the keyring search functions
      keys: Cache result of request_key*() temporarily in task_struct
      afs: Provide an RCU-capable key lookup
      afs: Support RCU pathwalk


 Documentation/security/keys/core.rst        |    8 ++
 Documentation/security/keys/request-key.rst |   11 +++
 fs/afs/dir.c                                |   54 ++++++++++++++
 fs/afs/internal.h                           |    1 
 fs/afs/security.c                           |  102 +++++++++++++++++++++++----
 include/keys/request_key_auth-type.h        |    1 
 include/linux/key.h                         |    3 +
 include/linux/sched.h                       |    5 +
 include/linux/tracehook.h                   |    5 +
 kernel/cred.c                               |    9 ++
 security/keys/internal.h                    |    6 +-
 security/keys/key.c                         |    4 +
 security/keys/keyring.c                     |   16 ++--
 security/keys/proc.c                        |    4 +
 security/keys/process_keys.c                |   41 +++++------
 security/keys/request_key.c                 |   97 +++++++++++++++++++++++++-
 security/keys/request_key_auth.c            |   60 ++++++++++------
 17 files changed, 346 insertions(+), 81 deletions(-)


^ permalink raw reply	[flat|nested] 7+ messages in thread

* [PATCH 1/6] keys: Fix request_key() lack of Link perm check on found key
  2019-05-22 22:46 [PATCH 0/6] keys: request_key() improvements(vspace)s David Howells
@ 2019-05-22 22:46 ` David Howells
  2019-05-22 22:46 ` [PATCH 2/6] keys: Invalidate used request_key authentication keys David Howells
                   ` (4 subsequent siblings)
  5 siblings, 0 replies; 7+ messages in thread
From: David Howells @ 2019-05-22 22:46 UTC (permalink / raw)
  To: keyrings; +Cc: dhowells, linux-afs, linux-security-module, linux-kernel

The request_key() syscall allows a process to gain access to the 'possessor'
permits of any key that grants it Search permission by virtue of request_key()
not checking whether a key it finds grants Link permission to the caller.

Signed-off-by: David Howells <dhowells@redhat.com>
---

 security/keys/request_key.c |   10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/security/keys/request_key.c b/security/keys/request_key.c
index e3653c6f85c6..d204d7c0152e 100644
--- a/security/keys/request_key.c
+++ b/security/keys/request_key.c
@@ -559,6 +559,16 @@ struct key *request_key_and_link(struct key_type *type,
 	key_ref = search_process_keyrings(&ctx);
 
 	if (!IS_ERR(key_ref)) {
+		if (dest_keyring) {
+			ret = key_task_permission(key_ref, current_cred(),
+						  KEY_NEED_LINK);
+			if (ret < 0) {
+				key_ref_put(key_ref);
+				key = ERR_PTR(ret);
+				goto error_free;
+			}
+		}
+
 		key = key_ref_to_ptr(key_ref);
 		if (dest_keyring) {
 			ret = key_link(dest_keyring, key);


^ permalink raw reply	[flat|nested] 7+ messages in thread

* [PATCH 2/6] keys: Invalidate used request_key authentication keys
  2019-05-22 22:46 [PATCH 0/6] keys: request_key() improvements(vspace)s David Howells
  2019-05-22 22:46 ` [PATCH 1/6] keys: Fix request_key() lack of Link perm check on found key David Howells
@ 2019-05-22 22:46 ` David Howells
  2019-05-22 22:46 ` [PATCH 3/6] keys: Move the RCU locks outwards from the keyring search functions David Howells
                   ` (3 subsequent siblings)
  5 siblings, 0 replies; 7+ messages in thread
From: David Howells @ 2019-05-22 22:46 UTC (permalink / raw)
  To: keyrings; +Cc: dhowells, linux-afs, linux-security-module, linux-kernel

Invalidate used request_key authentication keys rather than revoking them
so that they get cleaned up immediately rather than potentially hanging
around.  There doesn't seem any need to keep the revoked keys around.

Signed-off-by: David Howells <dhowells@redhat.com>
---

 security/keys/key.c         |    4 ++--
 security/keys/request_key.c |    2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/security/keys/key.c b/security/keys/key.c
index e0750bc85b68..00c7dbfc6a77 100644
--- a/security/keys/key.c
+++ b/security/keys/key.c
@@ -459,7 +459,7 @@ static int __key_instantiate_and_link(struct key *key,
 
 			/* disable the authorisation key */
 			if (authkey)
-				key_revoke(authkey);
+				key_invalidate(authkey);
 
 			if (prep->expiry != TIME64_MAX) {
 				key->expiry = prep->expiry;
@@ -607,7 +607,7 @@ int key_reject_and_link(struct key *key,
 
 		/* disable the authorisation key */
 		if (authkey)
-			key_revoke(authkey);
+			key_invalidate(authkey);
 	}
 
 	mutex_unlock(&key_construction_mutex);
diff --git a/security/keys/request_key.c b/security/keys/request_key.c
index d204d7c0152e..807c32b2c736 100644
--- a/security/keys/request_key.c
+++ b/security/keys/request_key.c
@@ -222,7 +222,7 @@ static int construct_key(struct key *key, const void *callout_info,
 	/* check that the actor called complete_request_key() prior to
 	 * returning an error */
 	WARN_ON(ret < 0 &&
-		!test_bit(KEY_FLAG_REVOKED, &authkey->flags));
+		!test_bit(KEY_FLAG_INVALIDATED, &authkey->flags));
 
 	key_put(authkey);
 	kleave(" = %d", ret);


^ permalink raw reply	[flat|nested] 7+ messages in thread

* [PATCH 3/6] keys: Move the RCU locks outwards from the keyring search functions
  2019-05-22 22:46 [PATCH 0/6] keys: request_key() improvements(vspace)s David Howells
  2019-05-22 22:46 ` [PATCH 1/6] keys: Fix request_key() lack of Link perm check on found key David Howells
  2019-05-22 22:46 ` [PATCH 2/6] keys: Invalidate used request_key authentication keys David Howells
@ 2019-05-22 22:46 ` David Howells
  2019-05-22 22:46 ` [PATCH 4/6] keys: Cache result of request_key*() temporarily in task_struct David Howells
                   ` (2 subsequent siblings)
  5 siblings, 0 replies; 7+ messages in thread
From: David Howells @ 2019-05-22 22:46 UTC (permalink / raw)
  To: keyrings; +Cc: dhowells, linux-afs, linux-security-module, linux-kernel

Move the RCU locks outwards from the keyring search functions so that a
request_key_rcu() function can be provided that searches for keys without
sleeping and without attempting to construct new keys.  This new function
must be invoked with the RCU read lock held.

Signed-off-by: David Howells <dhowells@redhat.com>
---

 Documentation/security/keys/core.rst        |    8 ++++
 Documentation/security/keys/request-key.rst |   11 +++++
 include/keys/request_key_auth-type.h        |    1 
 include/linux/key.h                         |    3 +
 security/keys/internal.h                    |    6 +--
 security/keys/keyring.c                     |   16 ++++---
 security/keys/proc.c                        |    4 +-
 security/keys/process_keys.c                |   41 ++++++++----------
 security/keys/request_key.c                 |   52 +++++++++++++++++++++++
 security/keys/request_key_auth.c            |   60 ++++++++++++++++-----------
 10 files changed, 141 insertions(+), 61 deletions(-)

diff --git a/Documentation/security/keys/core.rst b/Documentation/security/keys/core.rst
index 9521c4207f01..3b812be5ea1e 100644
--- a/Documentation/security/keys/core.rst
+++ b/Documentation/security/keys/core.rst
@@ -1121,6 +1121,14 @@ payload contents" for more information.
     If intr is true, then the wait can be interrupted by a signal, in which
     case error ERESTARTSYS will be returned.
 
+ *  To search for a key under RCU conditions, call::
+
+	struct key *request_key_rcu(const struct key_type *type,
+				    const char *description);
+
+    which is similar to request_key() except that it does not check for keys
+    that are under construction and it will not call out to userspace to
+    construct a key if it can't find a match.
 
  *  When it is no longer required, the key should be released using::
 
diff --git a/Documentation/security/keys/request-key.rst b/Documentation/security/keys/request-key.rst
index 600ad67d1707..2147f5ffb40f 100644
--- a/Documentation/security/keys/request-key.rst
+++ b/Documentation/security/keys/request-key.rst
@@ -36,6 +36,11 @@ or::
 					     	   size_t callout_len,
 						   void *aux);
 
+or::
+
+	struct key *request_key_rcu(const struct key_type *type,
+				    const char *description);
+
 Or by userspace invoking the request_key system call::
 
 	key_serial_t request_key(const char *type,
@@ -57,6 +62,10 @@ The two async in-kernel calls may return keys that are still in the process of
 being constructed.  The two non-async ones will wait for construction to
 complete first.
 
+The *_rcu() call is like the in-kernel request_key() call, except that it
+doesn't check for keys that are under construction and doesn't attempt to
+construct missing keys.
+
 The userspace interface links the key to a keyring associated with the process
 to prevent the key from going away, and returns the serial number of the key to
 the caller.
@@ -148,7 +157,7 @@ The Search Algorithm
 
 A search of any particular keyring proceeds in the following fashion:
 
-  1) When the key management code searches for a key (keyring_search_aux) it
+  1) When the key management code searches for a key (keyring_search_rcu) it
      firstly calls key_permission(SEARCH) on the keyring it's starting with,
      if this denies permission, it doesn't search further.
 
diff --git a/include/keys/request_key_auth-type.h b/include/keys/request_key_auth-type.h
index a726dd3f1dc6..2a046062bb42 100644
--- a/include/keys/request_key_auth-type.h
+++ b/include/keys/request_key_auth-type.h
@@ -18,6 +18,7 @@
  * Authorisation record for request_key().
  */
 struct request_key_auth {
+	struct rcu_head		rcu;
 	struct key		*target_key;
 	struct key		*dest_keyring;
 	const struct cred	*cred;
diff --git a/include/linux/key.h b/include/linux/key.h
index 612e1cf84049..3604a554df99 100644
--- a/include/linux/key.h
+++ b/include/linux/key.h
@@ -274,6 +274,9 @@ extern struct key *request_key(struct key_type *type,
 			       const char *description,
 			       const char *callout_info);
 
+extern struct key *request_key_rcu(struct key_type *type,
+				   const char *description);
+
 extern struct key *request_key_with_auxdata(struct key_type *type,
 					    const char *description,
 					    const void *callout_info,
diff --git a/security/keys/internal.h b/security/keys/internal.h
index 821819b4ee13..fd75b051d02a 100644
--- a/security/keys/internal.h
+++ b/security/keys/internal.h
@@ -135,11 +135,11 @@ struct keyring_search_context {
 
 extern bool key_default_cmp(const struct key *key,
 			    const struct key_match_data *match_data);
-extern key_ref_t keyring_search_aux(key_ref_t keyring_ref,
+extern key_ref_t keyring_search_rcu(key_ref_t keyring_ref,
 				    struct keyring_search_context *ctx);
 
-extern key_ref_t search_my_process_keyrings(struct keyring_search_context *ctx);
-extern key_ref_t search_process_keyrings(struct keyring_search_context *ctx);
+extern key_ref_t search_cred_keyrings_rcu(struct keyring_search_context *ctx);
+extern key_ref_t search_process_keyrings_rcu(struct keyring_search_context *ctx);
 
 extern struct key *find_keyring_by_name(const char *name, bool uid_keyring);
 
diff --git a/security/keys/keyring.c b/security/keys/keyring.c
index df3144f9c1aa..a086abba47a6 100644
--- a/security/keys/keyring.c
+++ b/security/keys/keyring.c
@@ -835,7 +835,7 @@ static bool search_nested_keyrings(struct key *keyring,
 }
 
 /**
- * keyring_search_aux - Search a keyring tree for a key matching some criteria
+ * keyring_search_rcu - Search a keyring tree for a matching key under RCU
  * @keyring_ref: A pointer to the keyring with possession indicator.
  * @ctx: The keyring search context.
  *
@@ -847,7 +847,9 @@ static bool search_nested_keyrings(struct key *keyring,
  * addition, the LSM gets to forbid keyring searches and key matches.
  *
  * The search is performed as a breadth-then-depth search up to the prescribed
- * limit (KEYRING_SEARCH_MAX_DEPTH).
+ * limit (KEYRING_SEARCH_MAX_DEPTH).  The caller must hold the RCU read lock to
+ * prevent keyrings from being destroyed or rearranged whilst they are being
+ * searched.
  *
  * Keys are matched to the type provided and are then filtered by the match
  * function, which is given the description to use in any way it sees fit.  The
@@ -866,7 +868,7 @@ static bool search_nested_keyrings(struct key *keyring,
  * In the case of a successful return, the possession attribute from
  * @keyring_ref is propagated to the returned key reference.
  */
-key_ref_t keyring_search_aux(key_ref_t keyring_ref,
+key_ref_t keyring_search_rcu(key_ref_t keyring_ref,
 			     struct keyring_search_context *ctx)
 {
 	struct key *keyring;
@@ -888,11 +890,9 @@ key_ref_t keyring_search_aux(key_ref_t keyring_ref,
 			return ERR_PTR(err);
 	}
 
-	rcu_read_lock();
 	ctx->now = ktime_get_real_seconds();
 	if (search_nested_keyrings(keyring, ctx))
 		__key_get(key_ref_to_ptr(ctx->result));
-	rcu_read_unlock();
 	return ctx->result;
 }
 
@@ -902,7 +902,7 @@ key_ref_t keyring_search_aux(key_ref_t keyring_ref,
  * @type: The type of keyring we want to find.
  * @description: The name of the keyring we want to find.
  *
- * As keyring_search_aux() above, but using the current task's credentials and
+ * As keyring_search_rcu() above, but using the current task's credentials and
  * type's default matching function and preferred search method.
  */
 key_ref_t keyring_search(key_ref_t keyring,
@@ -928,7 +928,9 @@ key_ref_t keyring_search(key_ref_t keyring,
 			return ERR_PTR(ret);
 	}
 
-	key = keyring_search_aux(keyring, &ctx);
+	rcu_read_lock();
+	key = keyring_search_rcu(keyring, &ctx);
+	rcu_read_unlock();
 
 	if (type->match_free)
 		type->match_free(&ctx.match_data);
diff --git a/security/keys/proc.c b/security/keys/proc.c
index 78ac305d715e..f081dceae3b9 100644
--- a/security/keys/proc.c
+++ b/security/keys/proc.c
@@ -179,7 +179,9 @@ static int proc_keys_show(struct seq_file *m, void *v)
 	 * skip if the key does not indicate the possessor can view it
 	 */
 	if (key->perm & KEY_POS_VIEW) {
-		skey_ref = search_my_process_keyrings(&ctx);
+		rcu_read_lock();
+		skey_ref = search_cred_keyrings_rcu(&ctx);
+		rcu_read_unlock();
 		if (!IS_ERR(skey_ref)) {
 			key_ref_put(skey_ref);
 			key_ref = make_key_ref(key, 1);
diff --git a/security/keys/process_keys.c b/security/keys/process_keys.c
index ba5d3172cafe..fb31b408e294 100644
--- a/security/keys/process_keys.c
+++ b/security/keys/process_keys.c
@@ -318,7 +318,8 @@ void key_fsgid_changed(struct cred *new_cred)
 
 /*
  * Search the process keyrings attached to the supplied cred for the first
- * matching key.
+ * matching key under RCU conditions (the caller must be holding the RCU read
+ * lock).
  *
  * The search criteria are the type and the match function.  The description is
  * given to the match function as a parameter, but doesn't otherwise influence
@@ -337,7 +338,7 @@ void key_fsgid_changed(struct cred *new_cred)
  * In the case of a successful return, the possession attribute is set on the
  * returned key reference.
  */
-key_ref_t search_my_process_keyrings(struct keyring_search_context *ctx)
+key_ref_t search_cred_keyrings_rcu(struct keyring_search_context *ctx)
 {
 	key_ref_t key_ref, ret, err;
 	const struct cred *cred = ctx->cred;
@@ -355,7 +356,7 @@ key_ref_t search_my_process_keyrings(struct keyring_search_context *ctx)
 
 	/* search the thread keyring first */
 	if (cred->thread_keyring) {
-		key_ref = keyring_search_aux(
+		key_ref = keyring_search_rcu(
 			make_key_ref(cred->thread_keyring, 1), ctx);
 		if (!IS_ERR(key_ref))
 			goto found;
@@ -373,7 +374,7 @@ key_ref_t search_my_process_keyrings(struct keyring_search_context *ctx)
 
 	/* search the process keyring second */
 	if (cred->process_keyring) {
-		key_ref = keyring_search_aux(
+		key_ref = keyring_search_rcu(
 			make_key_ref(cred->process_keyring, 1), ctx);
 		if (!IS_ERR(key_ref))
 			goto found;
@@ -394,7 +395,7 @@ key_ref_t search_my_process_keyrings(struct keyring_search_context *ctx)
 
 	/* search the session keyring */
 	if (cred->session_keyring) {
-		key_ref = keyring_search_aux(
+		key_ref = keyring_search_rcu(
 			make_key_ref(cred->session_keyring, 1), ctx);
 
 		if (!IS_ERR(key_ref))
@@ -415,7 +416,7 @@ key_ref_t search_my_process_keyrings(struct keyring_search_context *ctx)
 	}
 	/* or search the user-session keyring */
 	else if (READ_ONCE(cred->user->session_keyring)) {
-		key_ref = keyring_search_aux(
+		key_ref = keyring_search_rcu(
 			make_key_ref(READ_ONCE(cred->user->session_keyring), 1),
 			ctx);
 		if (!IS_ERR(key_ref))
@@ -448,16 +449,16 @@ key_ref_t search_my_process_keyrings(struct keyring_search_context *ctx)
  * the keys attached to the assumed authorisation key using its credentials if
  * one is available.
  *
- * Return same as search_my_process_keyrings().
+ * The caller must be holding the RCU read lock.
+ *
+ * Return same as search_cred_keyrings_rcu().
  */
-key_ref_t search_process_keyrings(struct keyring_search_context *ctx)
+key_ref_t search_process_keyrings_rcu(struct keyring_search_context *ctx)
 {
 	struct request_key_auth *rka;
 	key_ref_t key_ref, ret = ERR_PTR(-EACCES), err;
 
-	might_sleep();
-
-	key_ref = search_my_process_keyrings(ctx);
+	key_ref = search_cred_keyrings_rcu(ctx);
 	if (!IS_ERR(key_ref))
 		goto found;
 	err = key_ref;
@@ -472,24 +473,17 @@ key_ref_t search_process_keyrings(struct keyring_search_context *ctx)
 	    ) {
 		const struct cred *cred = ctx->cred;
 
-		/* defend against the auth key being revoked */
-		down_read(&cred->request_key_auth->sem);
-
-		if (key_validate(ctx->cred->request_key_auth) == 0) {
+		if (key_validate(cred->request_key_auth) == 0) {
 			rka = ctx->cred->request_key_auth->payload.data[0];
 
+			//// was search_process_keyrings() [ie. recursive]
 			ctx->cred = rka->cred;
-			key_ref = search_process_keyrings(ctx);
+			key_ref = search_cred_keyrings_rcu(ctx);
 			ctx->cred = cred;
 
-			up_read(&cred->request_key_auth->sem);
-
 			if (!IS_ERR(key_ref))
 				goto found;
-
 			ret = key_ref;
-		} else {
-			up_read(&cred->request_key_auth->sem);
 		}
 	}
 
@@ -504,7 +498,6 @@ key_ref_t search_process_keyrings(struct keyring_search_context *ctx)
 found:
 	return key_ref;
 }
-
 /*
  * See if the key we're looking at is the target key.
  */
@@ -693,7 +686,9 @@ key_ref_t lookup_user_key(key_serial_t id, unsigned long lflags,
 		ctx.index_key.desc_len		= strlen(key->description);
 		ctx.match_data.raw_data		= key;
 		kdebug("check possessed");
-		skey_ref = search_process_keyrings(&ctx);
+		rcu_read_lock();
+		skey_ref = search_process_keyrings_rcu(&ctx);
+		rcu_read_unlock();
 		kdebug("possessed=%p", skey_ref);
 
 		if (!IS_ERR(skey_ref)) {
diff --git a/security/keys/request_key.c b/security/keys/request_key.c
index 807c32b2c736..59a4e533e76a 100644
--- a/security/keys/request_key.c
+++ b/security/keys/request_key.c
@@ -382,7 +382,9 @@ static int construct_alloc_key(struct keyring_search_context *ctx,
 	 * waited for locks */
 	mutex_lock(&key_construction_mutex);
 
-	key_ref = search_process_keyrings(ctx);
+	rcu_read_lock();
+	key_ref = search_process_keyrings_rcu(ctx);
+	rcu_read_unlock();
 	if (!IS_ERR(key_ref))
 		goto key_already_present;
 
@@ -556,7 +558,9 @@ struct key *request_key_and_link(struct key_type *type,
 	}
 
 	/* search all the process keyrings for a key */
-	key_ref = search_process_keyrings(&ctx);
+	rcu_read_lock();
+	key_ref = search_process_keyrings_rcu(&ctx);
+	rcu_read_unlock();
 
 	if (!IS_ERR(key_ref)) {
 		if (dest_keyring) {
@@ -747,3 +751,47 @@ struct key *request_key_async_with_auxdata(struct key_type *type,
 				    callout_len, aux, NULL, KEY_ALLOC_IN_QUOTA);
 }
 EXPORT_SYMBOL(request_key_async_with_auxdata);
+
+/**
+ * request_key_rcu - Request key from RCU-read-locked context
+ * @type: The type of key we want.
+ * @description: The name of the key we want.
+ *
+ * Request a key from a context that we may not sleep in (such as RCU-mode
+ * pathwalk).  Keys under construction are ignored.
+ *
+ * Return a pointer to the found key if successful, -ENOKEY if we couldn't find
+ * a key or some other error if the key found was unsuitable or inaccessible.
+ */
+struct key *request_key_rcu(struct key_type *type, const char *description)
+{
+	struct keyring_search_context ctx = {
+		.index_key.type		= type,
+		.index_key.description	= description,
+		.index_key.desc_len	= strlen(description),
+		.cred			= current_cred(),
+		.match_data.cmp		= key_default_cmp,
+		.match_data.raw_data	= description,
+		.match_data.lookup_type	= KEYRING_SEARCH_LOOKUP_DIRECT,
+		.flags			= (KEYRING_SEARCH_DO_STATE_CHECK |
+					   KEYRING_SEARCH_SKIP_EXPIRED),
+	};
+	struct key *key;
+	key_ref_t key_ref;
+
+	kenter("%s,%s", type->name, description);
+
+	/* search all the process keyrings for a key */
+	key_ref = search_process_keyrings_rcu(&ctx);
+	if (IS_ERR(key_ref)) {
+		key = ERR_CAST(key_ref);
+		if (PTR_ERR(key_ref) == -EAGAIN)
+			key = ERR_PTR(-ENOKEY);
+	} else {
+		key = key_ref_to_ptr(key_ref);
+	}
+
+	kleave(" = %p", key);
+	return key;
+}
+EXPORT_SYMBOL(request_key_rcu);
diff --git a/security/keys/request_key_auth.c b/security/keys/request_key_auth.c
index ec5226557023..99ed7a8a273d 100644
--- a/security/keys/request_key_auth.c
+++ b/security/keys/request_key_auth.c
@@ -58,7 +58,7 @@ static void request_key_auth_free_preparse(struct key_preparsed_payload *prep)
 static int request_key_auth_instantiate(struct key *key,
 					struct key_preparsed_payload *prep)
 {
-	key->payload.data[0] = (struct request_key_auth *)prep->data;
+	rcu_assign_keypointer(key, (struct request_key_auth *)prep->data);
 	return 0;
 }
 
@@ -68,7 +68,7 @@ static int request_key_auth_instantiate(struct key *key,
 static void request_key_auth_describe(const struct key *key,
 				      struct seq_file *m)
 {
-	struct request_key_auth *rka = get_request_key_auth(key);
+	struct request_key_auth *rka = dereference_key_rcu(key);
 
 	seq_puts(m, "key:");
 	seq_puts(m, key->description);
@@ -83,7 +83,7 @@ static void request_key_auth_describe(const struct key *key,
 static long request_key_auth_read(const struct key *key,
 				  char __user *buffer, size_t buflen)
 {
-	struct request_key_auth *rka = get_request_key_auth(key);
+	struct request_key_auth *rka = dereference_key_locked(key);
 	size_t datalen;
 	long ret;
 
@@ -102,23 +102,6 @@ static long request_key_auth_read(const struct key *key,
 	return ret;
 }
 
-/*
- * Handle revocation of an authorisation token key.
- *
- * Called with the key sem write-locked.
- */
-static void request_key_auth_revoke(struct key *key)
-{
-	struct request_key_auth *rka = get_request_key_auth(key);
-
-	kenter("{%d}", key->serial);
-
-	if (rka->cred) {
-		put_cred(rka->cred);
-		rka->cred = NULL;
-	}
-}
-
 static void free_request_key_auth(struct request_key_auth *rka)
 {
 	if (!rka)
@@ -131,16 +114,43 @@ static void free_request_key_auth(struct request_key_auth *rka)
 	kfree(rka);
 }
 
+/*
+ * Dispose of the request_key_auth record under RCU conditions
+ */
+static void request_key_auth_rcu_disposal(struct rcu_head *rcu)
+{
+	struct request_key_auth *rka =
+		container_of(rcu, struct request_key_auth, rcu);
+
+	free_request_key_auth(rka);
+}
+
+/*
+ * Handle revocation of an authorisation token key.
+ *
+ * Called with the key sem write-locked.
+ */
+static void request_key_auth_revoke(struct key *key)
+{
+	struct request_key_auth *rka = dereference_key_locked(key);
+
+	kenter("{%d}", key->serial);
+	rcu_assign_keypointer(key, NULL);
+	call_rcu(&rka->rcu, request_key_auth_rcu_disposal);
+}
+
 /*
  * Destroy an instantiation authorisation token key.
  */
 static void request_key_auth_destroy(struct key *key)
 {
-	struct request_key_auth *rka = get_request_key_auth(key);
+	struct request_key_auth *rka = rcu_access_pointer(key->payload.rcu_data0);
 
 	kenter("{%d}", key->serial);
-
-	free_request_key_auth(rka);
+	if (rka) {
+		rcu_assign_keypointer(key, NULL);
+		call_rcu(&rka->rcu, request_key_auth_rcu_disposal);
+	}
 }
 
 /*
@@ -249,7 +259,9 @@ struct key *key_get_instantiation_authkey(key_serial_t target_id)
 
 	ctx.index_key.desc_len = sprintf(description, "%x", target_id);
 
-	authkey_ref = search_process_keyrings(&ctx);
+	rcu_read_lock();
+	authkey_ref = search_process_keyrings_rcu(&ctx);
+	rcu_read_unlock();
 
 	if (IS_ERR(authkey_ref)) {
 		authkey = ERR_CAST(authkey_ref);


^ permalink raw reply	[flat|nested] 7+ messages in thread

* [PATCH 4/6] keys: Cache result of request_key*() temporarily in task_struct
  2019-05-22 22:46 [PATCH 0/6] keys: request_key() improvements(vspace)s David Howells
                   ` (2 preceding siblings ...)
  2019-05-22 22:46 ` [PATCH 3/6] keys: Move the RCU locks outwards from the keyring search functions David Howells
@ 2019-05-22 22:46 ` David Howells
  2019-05-22 22:46 ` [PATCH 5/6] afs: Provide an RCU-capable key lookup David Howells
  2019-05-22 22:46 ` [PATCH 6/6] afs: Support RCU pathwalk David Howells
  5 siblings, 0 replies; 7+ messages in thread
From: David Howells @ 2019-05-22 22:46 UTC (permalink / raw)
  To: keyrings; +Cc: dhowells, linux-afs, linux-security-module, linux-kernel

If a filesystem uses keys to hold authentication tokens, then it needs a
token for each VFS operation that might perform an authentication check -
either by passing it to the server, or using to perform a check based on
authentication data cached locally.

For open files this isn't a problem, since the key should be cached in the
file struct since it represents the subject performing operations on that
file descriptor.

During pathwalk, however, there isn't anywhere to cache the key, except
perhaps in the nameidata struct - but that isn't exposed to the
filesystems.  Further, a pathwalk can incur a lot of operations, calling
one or more of the following, for instance:

	->lookup()
	->permission()
	->d_revalidate()
	->d_automount()
	->get_acl()
	->getxattr()

on each dentry/inode it encounters - and each one may need to call
request_key().  And then, at the end of pathwalk, it will call the actual
operation:

	->mkdir()
	->mknod()
	->getattr()
	->open()
	...

which may need to go and get the token again.

However, it is very likely that all of the operations on a single
dentry/inode - and quite possibly a sequence of them - will all want to use
the same authentication token, which suggests that caching it would be a
good idea.

To this end:

 (1) Make it so that a positive result of request_key() and co. that didn't
     require upcalling to userspace is cached temporarily in task_struct.

 (2) The cache is 1 deep, so a new result displaces the old one.

 (3) The key is released by exit and by notify-resume.

 (4) The cache is cleared in a newly forked process.

Signed-off-by: David Howells <dhowells@redhat.com>
---

 include/linux/sched.h       |    5 +++++
 include/linux/tracehook.h   |    5 +++++
 kernel/cred.c               |    9 +++++++++
 security/keys/request_key.c |   33 +++++++++++++++++++++++++++++++++
 4 files changed, 52 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 11837410690f..e5f18857dd53 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -831,6 +831,11 @@ struct task_struct {
 	/* Effective (overridable) subjective task credentials (COW): */
 	const struct cred __rcu		*cred;
 
+#ifdef CONFIG_KEYS
+	/* Cached requested key. */
+	struct key			*cached_requested_key;
+#endif
+
 	/*
 	 * executable name, excluding path.
 	 *
diff --git a/include/linux/tracehook.h b/include/linux/tracehook.h
index df20f8bdbfa3..ef497a94086c 100644
--- a/include/linux/tracehook.h
+++ b/include/linux/tracehook.h
@@ -187,6 +187,11 @@ static inline void tracehook_notify_resume(struct pt_regs *regs)
 	if (unlikely(current->task_works))
 		task_work_run();
 
+	if (unlikely(current->cached_requested_key)) {
+		key_put(current->cached_requested_key);
+		current->cached_requested_key = NULL;
+	}
+
 	mem_cgroup_handle_over_high();
 	blkcg_maybe_throttle_current();
 }
diff --git a/kernel/cred.c b/kernel/cred.c
index 3bd40de9e192..20e0cd54aad2 100644
--- a/kernel/cred.c
+++ b/kernel/cred.c
@@ -174,6 +174,11 @@ void exit_creds(struct task_struct *tsk)
 	validate_creds(cred);
 	alter_cred_subscribers(cred, -1);
 	put_cred(cred);
+
+#ifdef CONFIG_KEYS
+	key_put(current->cached_requested_key);
+	current->cached_requested_key = NULL;
+#endif
 }
 
 /**
@@ -327,6 +332,10 @@ int copy_creds(struct task_struct *p, unsigned long clone_flags)
 	struct cred *new;
 	int ret;
 
+#ifdef CONFIG_KEYS
+	p->cached_requested_key = NULL;
+#endif
+
 	if (
 #ifdef CONFIG_KEYS
 		!p->cred->thread_keyring &&
diff --git a/security/keys/request_key.c b/security/keys/request_key.c
index 59a4e533e76a..855de14974c3 100644
--- a/security/keys/request_key.c
+++ b/security/keys/request_key.c
@@ -22,6 +22,27 @@
 
 #define key_negative_timeout	60	/* default timeout on a negative key's existence */
 
+static struct key *check_cached_key(struct keyring_search_context *ctx)
+{
+	struct key *key = current->cached_requested_key;
+
+	if (key &&
+	    ctx->match_data.cmp(key, &ctx->match_data) &&
+	    !(key->flags & ((1 << KEY_FLAG_INVALIDATED) |
+			    (1 << KEY_FLAG_REVOKED))))
+		return key_get(key);
+	return NULL;
+}
+
+static void cache_requested_key(struct key *key)
+{
+	struct task_struct *t = current;
+
+	key_put(t->cached_requested_key);
+	t->cached_requested_key = key_get(key);
+	set_tsk_thread_flag(t, TIF_NOTIFY_RESUME);
+}
+
 /**
  * complete_request_key - Complete the construction of a key.
  * @authkey: The authorisation key.
@@ -557,6 +578,10 @@ struct key *request_key_and_link(struct key_type *type,
 		}
 	}
 
+	key = check_cached_key(&ctx);
+	if (key)
+		return key;
+
 	/* search all the process keyrings for a key */
 	rcu_read_lock();
 	key_ref = search_process_keyrings_rcu(&ctx);
@@ -582,6 +607,9 @@ struct key *request_key_and_link(struct key_type *type,
 				goto error_free;
 			}
 		}
+
+		/* Only cache the key on immediate success */
+		cache_requested_key(key);
 	} else if (PTR_ERR(key_ref) != -EAGAIN) {
 		key = ERR_CAST(key_ref);
 	} else  {
@@ -781,6 +809,10 @@ struct key *request_key_rcu(struct key_type *type, const char *description)
 
 	kenter("%s,%s", type->name, description);
 
+	key = check_cached_key(&ctx);
+	if (key)
+		return key;
+
 	/* search all the process keyrings for a key */
 	key_ref = search_process_keyrings_rcu(&ctx);
 	if (IS_ERR(key_ref)) {
@@ -789,6 +821,7 @@ struct key *request_key_rcu(struct key_type *type, const char *description)
 			key = ERR_PTR(-ENOKEY);
 	} else {
 		key = key_ref_to_ptr(key_ref);
+		cache_requested_key(key);
 	}
 
 	kleave(" = %p", key);


^ permalink raw reply	[flat|nested] 7+ messages in thread

* [PATCH 5/6] afs: Provide an RCU-capable key lookup
  2019-05-22 22:46 [PATCH 0/6] keys: request_key() improvements(vspace)s David Howells
                   ` (3 preceding siblings ...)
  2019-05-22 22:46 ` [PATCH 4/6] keys: Cache result of request_key*() temporarily in task_struct David Howells
@ 2019-05-22 22:46 ` David Howells
  2019-05-22 22:46 ` [PATCH 6/6] afs: Support RCU pathwalk David Howells
  5 siblings, 0 replies; 7+ messages in thread
From: David Howells @ 2019-05-22 22:46 UTC (permalink / raw)
  To: keyrings; +Cc: dhowells, linux-afs, linux-security-module, linux-kernel

Provide an RCU-capable key lookup function.  We don't want to call
afs_request_key() in RCU-mode pathwalk as request_key() might sleep, even if
we don't ask it to construct anything as it might find a key that is currently
undergoing construction.

Signed-off-by: David Howells <dhowells@redhat.com>
---

 fs/afs/internal.h |    1 +
 fs/afs/security.c |   27 +++++++++++++++++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/fs/afs/internal.h b/fs/afs/internal.h
index 2073c1a3ab4b..3090efcc823f 100644
--- a/fs/afs/internal.h
+++ b/fs/afs/internal.h
@@ -1237,6 +1237,7 @@ extern void afs_cache_permit(struct afs_vnode *, struct key *, unsigned int,
 			     struct afs_status_cb *);
 extern void afs_zap_permits(struct rcu_head *);
 extern struct key *afs_request_key(struct afs_cell *);
+extern struct key *afs_request_key_rcu(struct afs_cell *);
 extern int afs_check_permit(struct afs_vnode *, struct key *, afs_access_t *);
 extern int afs_permission(struct inode *, int);
 extern void __exit afs_clean_up_permit_cache(void);
diff --git a/fs/afs/security.c b/fs/afs/security.c
index 5d8ece98561e..a6582d6a3882 100644
--- a/fs/afs/security.c
+++ b/fs/afs/security.c
@@ -49,6 +49,33 @@ struct key *afs_request_key(struct afs_cell *cell)
 	}
 }
 
+/*
+ * Get a key when pathwalk is in rcuwalk mode.
+ */
+struct key *afs_request_key_rcu(struct afs_cell *cell)
+{
+	struct key *key;
+
+	_enter("{%x}", key_serial(cell->anonymous_key));
+
+	_debug("key %s", cell->anonymous_key->description);
+	key = request_key_rcu(&key_type_rxrpc, cell->anonymous_key->description);
+	if (IS_ERR(key)) {
+		if (PTR_ERR(key) != -ENOKEY) {
+			_leave(" = %ld", PTR_ERR(key));
+			return key;
+		}
+
+		/* act as anonymous user */
+		_leave(" = {%x} [anon]", key_serial(cell->anonymous_key));
+		return cell->anonymous_key;
+	} else {
+		/* act as authorised user */
+		_leave(" = {%x} [auth]", key_serial(key));
+		return key;
+	}
+}
+
 /*
  * Dispose of a list of permits.
  */


^ permalink raw reply	[flat|nested] 7+ messages in thread

* [PATCH 6/6] afs: Support RCU pathwalk
  2019-05-22 22:46 [PATCH 0/6] keys: request_key() improvements(vspace)s David Howells
                   ` (4 preceding siblings ...)
  2019-05-22 22:46 ` [PATCH 5/6] afs: Provide an RCU-capable key lookup David Howells
@ 2019-05-22 22:46 ` David Howells
  5 siblings, 0 replies; 7+ messages in thread
From: David Howells @ 2019-05-22 22:46 UTC (permalink / raw)
  To: keyrings; +Cc: dhowells, linux-afs, linux-security-module, linux-kernel

Make afs_permission() and afs_d_revalidate() do initial checks in RCU-mode
pathwalk to reduce latency in pathwalk elements that get done multiple
times.  We don't need to query the server unless we've received a
notification from it that something has changed or the callback has
expired.

This requires that we can request a key and check permits under RCU
conditions if we need to.

Signed-off-by: David Howells <dhowells@redhat.com>
---

 fs/afs/dir.c      |   54 +++++++++++++++++++++++++++++++++++++-
 fs/afs/security.c |   75 ++++++++++++++++++++++++++++++++++++++++++-----------
 2 files changed, 112 insertions(+), 17 deletions(-)

diff --git a/fs/afs/dir.c b/fs/afs/dir.c
index 79d93a26759a..c394e7c1a8ab 100644
--- a/fs/afs/dir.c
+++ b/fs/afs/dir.c
@@ -961,6 +961,58 @@ static struct dentry *afs_lookup(struct inode *dir, struct dentry *dentry,
 	return d;
 }
 
+/*
+ * Check the validity of a dentry under RCU conditions.
+ */
+static int afs_d_revalidate_rcu(struct dentry *dentry)
+{
+	struct afs_vnode *dvnode, *vnode;
+	struct dentry *parent;
+	struct inode *dir, *inode;
+	long dir_version, de_version;
+
+	_enter("%p", dentry);
+
+	/* Check the parent directory is still valid first. */
+	parent = READ_ONCE(dentry->d_parent);
+	dir = d_inode_rcu(parent);
+	if (!dir)
+		return -ECHILD;
+	dvnode = AFS_FS_I(dir);
+	if (test_bit(AFS_VNODE_DELETED, &dvnode->flags))
+		return -ECHILD;
+
+	if (!afs_check_validity(dvnode))
+		return -ECHILD;
+
+	/* We only need to invalidate a dentry if the server's copy changed
+	 * behind our back.  If we made the change, it's no problem.  Note that
+	 * on a 32-bit system, we only have 32 bits in the dentry to store the
+	 * version.
+	 */
+	dir_version = (long)READ_ONCE(dvnode->status.data_version);
+	de_version = (long)READ_ONCE(dentry->d_fsdata);
+	if (de_version != dir_version) {
+		dir_version = (long)READ_ONCE(dvnode->invalid_before);
+		if (de_version - dir_version < 0)
+			return -ECHILD;
+	}
+
+	/* Check to see if the vnode referred to by the dentry still
+	 * has a callback.
+	 */
+	if (d_really_is_positive(dentry)) {
+		inode = d_inode_rcu(dentry);
+		if (inode) {
+			vnode = AFS_FS_I(inode);
+			if (!afs_check_validity(vnode))
+				return -ECHILD;
+		}
+	}
+
+	return 1; /* Still valid */
+}
+
 /*
  * check that a dentry lookup hit has found a valid entry
  * - NOTE! the hit can be a negative hit too, so we can't assume we have an
@@ -977,7 +1029,7 @@ static int afs_d_revalidate(struct dentry *dentry, unsigned int flags)
 	int ret;
 
 	if (flags & LOOKUP_RCU)
-		return -ECHILD;
+		return afs_d_revalidate_rcu(dentry);
 
 	if (d_really_is_positive(dentry)) {
 		vnode = AFS_FS_I(d_inode(dentry));
diff --git a/fs/afs/security.c b/fs/afs/security.c
index a6582d6a3882..fab44171344f 100644
--- a/fs/afs/security.c
+++ b/fs/afs/security.c
@@ -305,6 +305,40 @@ void afs_cache_permit(struct afs_vnode *vnode, struct key *key,
 	return;
 }
 
+static bool afs_check_permit_rcu(struct afs_vnode *vnode, struct key *key,
+				 afs_access_t *_access)
+{
+	const struct afs_permits *permits;
+	int i;
+
+	_enter("{%llx:%llu},%x",
+	       vnode->fid.vid, vnode->fid.vnode, key_serial(key));
+
+	/* check the permits to see if we've got one yet */
+	if (key == vnode->volume->cell->anonymous_key) {
+		*_access = vnode->status.anon_access;
+		_leave(" = t [anon %x]", *_access);
+		return true;
+	}
+
+	permits = rcu_dereference(vnode->permit_cache);
+	if (permits) {
+		for (i = 0; i < permits->nr_permits; i++) {
+			if (permits->permits[i].key < key)
+				continue;
+			if (permits->permits[i].key > key)
+				break;
+
+			*_access = permits->permits[i].access;
+			_leave(" = %u [perm %x]", !permits->invalidated, *_access);
+			return !permits->invalidated;
+		}
+	}
+
+	_leave(" = f");
+	return false;
+}
+
 /*
  * check with the fileserver to see if the directory or parent directory is
  * permitted to be accessed with this authorisation, and if so, what access it
@@ -371,33 +405,42 @@ int afs_permission(struct inode *inode, int mask)
 	struct afs_vnode *vnode = AFS_FS_I(inode);
 	afs_access_t uninitialized_var(access);
 	struct key *key;
-	int ret;
-
-	if (mask & MAY_NOT_BLOCK)
-		return -ECHILD;
+	int ret = 0;
 
 	_enter("{{%llx:%llu},%lx},%x,",
 	       vnode->fid.vid, vnode->fid.vnode, vnode->flags, mask);
 
-	key = afs_request_key(vnode->volume->cell);
-	if (IS_ERR(key)) {
-		_leave(" = %ld [key]", PTR_ERR(key));
-		return PTR_ERR(key);
-	}
+	if (mask & MAY_NOT_BLOCK) {
+		key = afs_request_key_rcu(vnode->volume->cell);
+		if (IS_ERR(key))
+			return -ECHILD;
 
-	ret = afs_validate(vnode, key);
-	if (ret < 0)
-		goto error;
+		ret = -ECHILD;
+		if (!afs_check_validity(vnode) ||
+		    !afs_check_permit_rcu(vnode, key, &access))
+			goto error;
+	} else {
+		key = afs_request_key(vnode->volume->cell);
+		if (IS_ERR(key)) {
+			_leave(" = %ld [key]", PTR_ERR(key));
+			return PTR_ERR(key);
+		}
 
-	/* check the permits to see if we've got one yet */
-	ret = afs_check_permit(vnode, key, &access);
-	if (ret < 0)
-		goto error;
+		ret = afs_validate(vnode, key);
+		if (ret < 0)
+			goto error;
+
+		/* check the permits to see if we've got one yet */
+		ret = afs_check_permit(vnode, key, &access);
+		if (ret < 0)
+			goto error;
+	}
 
 	/* interpret the access mask */
 	_debug("REQ %x ACC %x on %s",
 	       mask, access, S_ISDIR(inode->i_mode) ? "dir" : "file");
 
+	ret = 0;
 	if (S_ISDIR(inode->i_mode)) {
 		if (mask & (MAY_EXEC | MAY_READ | MAY_CHDIR)) {
 			if (!(access & AFS_ACE_LOOKUP))


^ permalink raw reply	[flat|nested] 7+ messages in thread

end of thread, other threads:[~2019-05-22 22:46 UTC | newest]

Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-05-22 22:46 [PATCH 0/6] keys: request_key() improvements(vspace)s David Howells
2019-05-22 22:46 ` [PATCH 1/6] keys: Fix request_key() lack of Link perm check on found key David Howells
2019-05-22 22:46 ` [PATCH 2/6] keys: Invalidate used request_key authentication keys David Howells
2019-05-22 22:46 ` [PATCH 3/6] keys: Move the RCU locks outwards from the keyring search functions David Howells
2019-05-22 22:46 ` [PATCH 4/6] keys: Cache result of request_key*() temporarily in task_struct David Howells
2019-05-22 22:46 ` [PATCH 5/6] afs: Provide an RCU-capable key lookup David Howells
2019-05-22 22:46 ` [PATCH 6/6] afs: Support RCU pathwalk David Howells

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