[RFC][PATCH] affs_lookup(): close a race with affs_remove_link()

[RFC][PATCH] affs_lookup(): close a race with affs_remove_link()

[Al Viro]

[#fixes unless somebody yells; -stable fodder and yes, it _is_ that old -
all way back to 2001]

we unlock the directory hash too early - if we are looking at secondary
link and primary (in another directory) gets removed just as we unlock,
we could have the old primary moved in place of the secondary, leaving
us to look into freed entry (and leaving our dentry with ->d_fsdata
pointing to a freed entry).

Cc: stable@vger.kernel.org # 2.4.4+
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/affs/namei.c b/fs/affs/namei.c
index d8aa0ae3d037..1ed0fa4c4d48 100644
--- a/fs/affs/namei.c
+++ b/fs/affs/namei.c
@@ -206,9 +206,10 @@ affs_lookup(struct inode *dir, struct dentry *dentry, unsigned int flags)
 
 	affs_lock_dir(dir);
 	bh = affs_find_entry(dir, dentry);
-	affs_unlock_dir(dir);
-	if (IS_ERR(bh))
+	if (IS_ERR(bh)) {
+		affs_unlock_dir(dir);
 		return ERR_CAST(bh);
+	}
 	if (bh) {
 		u32 ino = bh->b_blocknr;
 
@@ -222,10 +223,13 @@ affs_lookup(struct inode *dir, struct dentry *dentry, unsigned int flags)
 		}
 		affs_brelse(bh);
 		inode = affs_iget(sb, ino);
-		if (IS_ERR(inode))
+		if (IS_ERR(inode)) {
+			affs_unlock_dir(dir);
 			return ERR_CAST(inode);
+		}
 	}
 	d_add(dentry, inode);
+	affs_unlock_dir(dir);
 	return NULL;
 }
 

Re: [RFC][PATCH] affs_lookup(): close a race with affs_remove_link()

[David Sterba]

On Sun, May 13, 2018 at 05:00:40PM +0100, Al Viro wrote:
> [#fixes unless somebody yells; -stable fodder and yes, it _is_ that old -
> all way back to 2001]
> 
> we unlock the directory hash too early - if we are looking at secondary
> link and primary (in another directory) gets removed just as we unlock,
> we could have the old primary moved in place of the secondary, leaving
> us to look into freed entry (and leaving our dentry with ->d_fsdata
> pointing to a freed entry).
> 
> Cc: stable@vger.kernel.org # 2.4.4+
> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Sorry for the delay. As far as my limited knowledge of the AFFS code
goes, this change looks ok. You can add my

Acked-by: David Sterba <dsterba@suse.com>

and please take it through the vfs tree. Thanks.