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

[Al Viro <viro@ZenIV.linux.org.uk>]

[#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;
 }