LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Miklos Szeredi <miklos@szeredi.hu>
To: akpm@linux-foundation.org, serue@us.ibm.com,
	viro@ftp.linux.org.uk, linuxram@us.ibm.com,
	ebiederm@xmission.com, kzak@redhat.com
Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	containers@lists.osdl.org
Subject: [patch 07/10] unprivileged mounts: allow unprivileged mounts
Date: Fri, 27 Apr 2007 14:04:24 +0200	[thread overview]
Message-ID: <20070427120550.241509359@szeredi.hu> (raw)
In-Reply-To: <20070427120417.110164241@szeredi.hu>

[-- Attachment #1: unprivileged-mounts-allow-unprivileged-mounts.patch --]
[-- Type: text/plain, Size: 4156 bytes --]

From: Miklos Szeredi <mszeredi@suse.cz>

Define a new fs flag FS_SAFE, which denotes, that unprivileged mounting of
this filesystem may not constitute a security problem.

Since most filesystems haven't been designed with unprivileged mounting in
mind, a thorough audit is needed before setting this flag.

For "safe" filesystems also allow unprivileged forced unmounting.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
---

Index: linux/fs/namespace.c
===================================================================
--- linux.orig/fs/namespace.c	2007-04-26 13:30:04.000000000 +0200
+++ linux/fs/namespace.c	2007-04-26 13:51:29.000000000 +0200
@@ -724,14 +724,16 @@ static bool is_mount_owner(struct vfsmou
 /*
  * umount is permitted for
  *  - sysadmin
- *  - mount owner, if not forced umount
+ *  - mount owner
+ *    o if not forced umount,
+ *    o if forced umount, and filesystem is "safe"
  */
 static bool permit_umount(struct vfsmount *mnt, int flags)
 {
 	if (capable(CAP_SYS_ADMIN))
 		return true;
 
-	if (flags & MNT_FORCE)
+	if ((flags & MNT_FORCE) && !(mnt->mnt_sb->s_type->fs_flags & FS_SAFE))
 		return false;
 
 	return is_mount_owner(mnt, current->fsuid);
@@ -787,13 +789,17 @@ asmlinkage long sys_oldumount(char __use
  * - mountpoint is not a symlink
  * - mountpoint is in a mount owned by the user
  */
-static bool permit_mount(struct nameidata *nd, int *flags)
+static bool permit_mount(struct nameidata *nd, struct file_system_type *type,
+			 int *flags)
 {
 	struct inode *inode = nd->dentry->d_inode;
 
 	if (capable(CAP_SYS_ADMIN))
 		return true;
 
+	if (type && !(type->fs_flags & FS_SAFE))
+		return false;
+
 	if (S_ISLNK(inode->i_mode))
 		return false;
 
@@ -1027,7 +1033,7 @@ static int do_loopback(struct nameidata 
 	struct vfsmount *mnt = NULL;
 	int err;
 
-	if (!permit_mount(nd, &flags))
+	if (!permit_mount(nd, NULL, &flags))
 		return -EPERM;
 	if (!old_name || !*old_name)
 		return -EINVAL;
@@ -1188,26 +1194,46 @@ out:
  * create a new mount for userspace and request it to be added into the
  * namespace's tree
  */
-static int do_new_mount(struct nameidata *nd, char *type, int flags,
+static int do_new_mount(struct nameidata *nd, char *fstype, int flags,
 			int mnt_flags, char *name, void *data)
 {
+	int err;
 	struct vfsmount *mnt;
+	struct file_system_type *type;
 
-	if (!type || !memchr(type, 0, PAGE_SIZE))
+	if (!fstype || !memchr(fstype, 0, PAGE_SIZE))
 		return -EINVAL;
 
-	/* we need capabilities... */
-	if (!capable(CAP_SYS_ADMIN))
-		return -EPERM;
-
-	mnt = do_kern_mount(type, flags & ~MS_SETUSER, name, data);
-	if (IS_ERR(mnt))
+	type = get_fs_type(fstype);
+	if (!type)
+		return -ENODEV;
+
+	err = -EPERM;
+	if (!permit_mount(nd, type, &flags))
+		goto out_put_filesystem;
+
+	if (flags & MS_SETUSER) {
+		err = reserve_user_mount();
+		if (err)
+			goto out_put_filesystem;
+	}
+
+	mnt = vfs_kern_mount(type, flags & ~MS_SETUSER, name, data);
+	put_filesystem(type);
+	if (IS_ERR(mnt)) {
+		if (flags & MS_SETUSER)
+			dec_nr_user_mounts();
 		return PTR_ERR(mnt);
+	}
 
 	if (flags & MS_SETUSER)
-		set_mnt_user(mnt);
+		__set_mnt_user(mnt);
 
 	return do_add_mount(mnt, nd, mnt_flags, NULL);
+
+ out_put_filesystem:
+	put_filesystem(type);
+	return err;
 }
 
 /*
@@ -1237,7 +1263,7 @@ int do_add_mount(struct vfsmount *newmnt
 	if (S_ISLNK(newmnt->mnt_root->d_inode->i_mode))
 		goto unlock;
 
-	/* MNT_USER was set earlier */
+	/* some flags may have been set earlier */
 	newmnt->mnt_flags |= mnt_flags;
 	if ((err = graft_tree(newmnt, nd)))
 		goto unlock;
Index: linux/include/linux/fs.h
===================================================================
--- linux.orig/include/linux/fs.h	2007-04-26 13:46:26.000000000 +0200
+++ linux/include/linux/fs.h	2007-04-26 13:48:14.000000000 +0200
@@ -96,6 +96,7 @@ extern int dir_notify_enable;
 #define FS_REQUIRES_DEV 1 
 #define FS_BINARY_MOUNTDATA 2
 #define FS_HAS_SUBTYPE 4
+#define FS_SAFE 8		/* Safe to mount by unprivileged users */
 #define FS_REVAL_DOT	16384	/* Check the paths ".", ".." for staleness */
 #define FS_RENAME_DOES_D_MOVE	32768	/* FS will handle d_move()
 					 * during rename() internally.

--

  parent reply	other threads:[~2007-04-27 12:08 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-04-27 12:04 [patch 00/10] mount ownership and unprivileged mount syscall (v5) Miklos Szeredi
2007-04-27 12:04 ` [patch 01/10] unprivileged mounts: add user mounts to the kernel Miklos Szeredi
2007-04-27 12:04 ` [patch 02/10] unprivileged mounts: allow unprivileged umount Miklos Szeredi
2007-04-27 12:04 ` [patch 03/10] unprivileged mounts: account user mounts Miklos Szeredi
2007-04-27 12:04 ` [patch 04/10] unprivileged mounts: propagate error values from clone_mnt Miklos Szeredi
2007-04-27 12:04 ` [patch 05/10] unprivileged mounts: allow unprivileged bind mounts Miklos Szeredi
2007-04-27 12:04 ` [patch 06/10] unprivileged mounts: put declaration of put_filesystem() in fs.h Miklos Szeredi
2007-04-27 12:04 ` Miklos Szeredi [this message]
2007-04-27 12:04 ` [patch 08/10] unprivileged mounts: allow unprivileged fuse mounts Miklos Szeredi
2007-04-27 12:04 ` [patch 09/10] unprivileged mounts: propagation: inherit owner from parent Miklos Szeredi
2007-04-27 12:04 ` [patch 10/10] unprivileged mounts: add "no submounts" flag Miklos Szeredi

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20070427120550.241509359@szeredi.hu \
    --to=miklos@szeredi.hu \
    --cc=akpm@linux-foundation.org \
    --cc=containers@lists.osdl.org \
    --cc=ebiederm@xmission.com \
    --cc=kzak@redhat.com \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linuxram@us.ibm.com \
    --cc=serue@us.ibm.com \
    --cc=viro@ftp.linux.org.uk \
    --subject='Re: [patch 07/10] unprivileged mounts: allow unprivileged mounts' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).