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vfs: fix race in rcu lookup of pruned dentry 

Don't update *inode in __follow_mount_rcu() until we'd verified that
there is mountpoint there.  Kudos to Hugh Dickins for catching that
one in the first place and eventually figuring out the solution (and
catching a braino in the earlier version of patch).

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Linus Torvalds 2011-07-18 15:43:29 -07:00
parent fec11dd9a0
commit 5943026240
1 changed files with 6 additions and 1 deletions
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7
fs/namei.c
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@ -942,7 +942,6 @@ static bool __follow_mount_rcu(struct nameidata *nd, struct path *path,
* Don't forget we might have a non-mountpoint managed dentry
* that wants to block transit.
*/
*inode = path->dentry->d_inode;
if (unlikely(managed_dentry_might_block(path->dentry)))
return false;
@ -955,6 +954,12 @@ static bool __follow_mount_rcu(struct nameidata *nd, struct path *path,
path->mnt = mounted;
path->dentry = mounted->mnt_root;
nd->seq = read_seqcount_begin(&path->dentry->d_seq);
/*
* Update the inode too. We don't need to re-check the
* dentry sequence number here after this d_inode read,
* because a mount-point is always pinned.
*/
*inode = path->dentry->d_inode;
}
return true;
}