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From: Willy Tarreau <w@1wt.eu>
To: linux-kernel@vger.kernel.org, stable@kernel.org,
	stable-review@kernel.org
Cc: NeilBrown <neilb@suse.de>, "J. Bruce Fields" <bfields@redhat.com>,
	Greg Kroah-Hartman <gregkh@suse.de>, Willy Tarreau <w@1wt.eu>
Subject: [PATCH 18/23] sunrpc: prevent use-after-free on clearing XPT_BUSY
Date: Mon, 07 Feb 2011 00:23:10 +0100	[thread overview]
Message-ID: <20110206232253.294757001@pcw.home.local> (raw)
In-Reply-To: <4beed4da27f06efb2c13d6ed48850634@local>

2.6.27.58-stable review patch.  If anyone has any objections, please let us know.

------------------

From: NeilBrown <neilb@suse.de>

commit ed2849d3ecfa339435818eeff28f6c3424300cec upstream.

When an xprt is created, it has a refcount of 1, and XPT_BUSY is set.
The refcount is *not* owned by the thread that created the xprt
(as is clear from the fact that creators never put the reference).
Rather, it is owned by the absence of XPT_DEAD.  Once XPT_DEAD is set,
(And XPT_BUSY is clear) that initial reference is dropped and the xprt
can be freed.

So when a creator clears XPT_BUSY it is dropping its only reference and
so must not touch the xprt again.

However svc_recv, after calling ->xpo_accept (and so getting an XPT_BUSY
reference on a new xprt), calls svc_xprt_recieved.  This clears
XPT_BUSY and then svc_xprt_enqueue - this last without owning a reference.
This is dangerous and has been seen to leave svc_xprt_enqueue working
with an xprt containing garbage.

So we need to hold an extra counted reference over that call to
svc_xprt_received.

For safety, any time we clear XPT_BUSY and then use the xprt again, we
first get a reference, and the put it again afterwards.

Note that svc_close_all does not need this extra protection as there are
no threads running, and the final free can only be called asynchronously
from such a thread.

Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Willy Tarreau <w@1wt.eu>

---
 net/sunrpc/svc_xprt.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

Index: longterm-2.6.27/net/sunrpc/svc_xprt.c
===================================================================
--- longterm-2.6.27.orig/net/sunrpc/svc_xprt.c	2011-01-29 11:19:14.731064813 +0100
+++ longterm-2.6.27/net/sunrpc/svc_xprt.c	2011-01-29 11:27:22.220064064 +0100
@@ -172,6 +172,7 @@
 	spin_lock(&svc_xprt_class_lock);
 	list_for_each_entry(xcl, &svc_xprt_class_list, xcl_list) {
 		struct svc_xprt *newxprt;
+		unsigned short newport;
 
 		if (strcmp(xprt_name, xcl->xcl_name))
 			continue;
@@ -192,8 +193,9 @@
 		spin_lock_bh(&serv->sv_lock);
 		list_add(&newxprt->xpt_list, &serv->sv_permsocks);
 		spin_unlock_bh(&serv->sv_lock);
+		newport = svc_xprt_local_port(newxprt);
 		clear_bit(XPT_BUSY, &newxprt->xpt_flags);
-		return svc_xprt_local_port(newxprt);
+		return newport;
 	}
  err:
 	spin_unlock(&svc_xprt_class_lock);
@@ -386,8 +388,13 @@
 {
 	BUG_ON(!test_bit(XPT_BUSY, &xprt->xpt_flags));
 	xprt->xpt_pool = NULL;
+	/* As soon as we clear busy, the xprt could be closed and
+	 * 'put', so we need a reference to call svc_xprt_enqueue with:
+	 */
+	svc_xprt_get(xprt);
 	clear_bit(XPT_BUSY, &xprt->xpt_flags);
 	svc_xprt_enqueue(xprt);
+	svc_xprt_put(xprt);
 }
 EXPORT_SYMBOL_GPL(svc_xprt_received);
 



  parent reply	other threads:[~2011-02-06 23:45 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20110206232252.509080428@pcw.home.local>
2011-02-06 23:22 ` [PATCH 00/23] 2.6.27.58-longterm review Willy Tarreau
2011-02-06 23:22   ` [PATCH 01/23] ALSA: hda: Use model=lg quirk for LG P1 Express to enable playback and capture Willy Tarreau
2011-02-06 23:22   ` [PATCH 02/23] ALSA: hda: Use LPIB for Dell Latitude 131L Willy Tarreau
2011-02-06 23:22   ` [PATCH 03/23] ALSA: hda: Use LPIB quirk for Dell Inspiron m101z/1120 Willy Tarreau
2011-02-06 23:22   ` [PATCH 04/23] USB: usb-storage: unusual_devs entry for the Samsung YP-CP3 Willy Tarreau
2011-02-06 23:22   ` [PATCH 05/23] USB: misc: uss720.c: add another vendor/product ID Willy Tarreau
2011-02-06 23:22   ` [PATCH 06/23] HID: hidraw: fix window in hidraw_release Willy Tarreau
2011-02-06 23:22   ` [PATCH 07/23] hwmon: (adm1026) Allow 1 as a valid divider value Willy Tarreau
2011-02-06 23:23   ` [PATCH 08/23] hwmon: (adm1026) Fix setting fan_div Willy Tarreau
2011-02-06 23:23   ` [PATCH 09/23] IB/uverbs: Handle large number of entries in poll CQ Willy Tarreau
2011-02-06 23:23   ` [PATCH 10/23] mv_xor: fix race in tasklet function Willy Tarreau
2011-02-06 23:23   ` [PATCH 11/23] md: fix bug with re-adding of partially recovered device Willy Tarreau
2011-02-06 23:23   ` [PATCH 12/23] NFS: Fix fcntl F_GETLK not reporting some conflicts Willy Tarreau
2011-02-06 23:23   ` [PATCH 13/23] nfsd: Fix possible BUG_ON firing in set_change_info Willy Tarreau
2011-02-06 23:23   ` [PATCH 14/23] PM / Hibernate: Fix PM_POST_* notification with user-space suspend Willy Tarreau
2011-02-06 23:23   ` [PATCH 15/23] posix-cpu-timers: workaround to suppress the problems with mt exec Willy Tarreau
2011-02-06 23:23   ` [PATCH 16/23] sctp: Fix a race between ICMP protocol unreachable and connect() Willy Tarreau
2011-02-06 23:23   ` [PATCH 17/23] sound: Prevent buffer overflow in OSS load_mixer_volumes Willy Tarreau
2011-02-06 23:23   ` Willy Tarreau [this message]
2011-02-06 23:23   ` [PATCH 19/23] x86, gcc-4.6: Use gcc -m options when building vdso Willy Tarreau
2011-02-06 23:23   ` [PATCH 20/23] tracing: Fix panic when lseek() called on "trace" opened for writing Willy Tarreau
2011-02-14 23:14     ` [Stable-review] " Ben Hutchings
2011-02-15  1:33       ` Steven Rostedt
2011-02-15  1:38         ` Ben Hutchings
2011-02-15  2:01           ` Steven Rostedt
2011-02-15  5:39       ` Willy Tarreau
2011-02-06 23:23   ` [PATCH 21/23] hvc_console: Fix race between hvc_close and hvc_remove Willy Tarreau
2011-02-07 21:16     ` Anton Blanchard
2011-02-07 22:11       ` Willy Tarreau
2011-02-06 23:23   ` [PATCH 22/23] hvc_console: Fix race between hvc_close and hvc_remove, again Willy Tarreau
2011-02-06 23:23   ` [PATCH 23/23] install_special_mapping skips security_file_mmap check Willy Tarreau

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