From: Linus Torvalds Date: Mon, 18 Jul 2011 22:43:29 +0000 (-0700) Subject: vfs: fix race in rcu lookup of pruned dentry X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=59430262401bec02d415179c43dbe5b8819c09ce;p=linux-beck.git 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 Signed-off-by: Al Viro --- diff --git a/fs/namei.c b/fs/namei.c index 5c867dd1c0b3..14ab8d3f2f0c 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -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; }