linux-kernel - [PATCH 3.16 340/366] affs_lookup(): close a race with affs_remove

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Message-ID: <lsq.1539530741.533778459@decadent.org.uk>
Date:   Sun, 14 Oct 2018 16:25:41 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Al Viro" <viro@...iv.linux.org.uk>,
        "David Sterba" <dsterba@...e.com>
Subject: [PATCH 3.16 340/366] affs_lookup(): close a race with
 affs_remove_link()

3.16.60-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Al Viro <viro@...iv.linux.org.uk>

commit 30da870ce4a4e007c901858a96e9e394a1daa74a upstream.

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).

Acked-by: David Sterba <dsterba@...e.com>
Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/affs/namei.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

--- a/fs/affs/namei.c
+++ b/fs/affs/namei.c
@@ -224,9 +224,10 @@ affs_lookup(struct inode *dir, struct de
 
 	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;
 
@@ -240,10 +241,13 @@ affs_lookup(struct inode *dir, struct de
 		}
 		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;
 }