[PATCH] Btrfs: fix log context list corruption after rename whiteout error

[PATCH] Btrfs: fix log context list corruption after rename whiteout error

[fdmanana]

From: Filipe Manana <fdmanana@suse.com>

During a rename whiteout, if btrfs_whiteout_for_rename() returns an error
we can end up returning from btrfs_rename() with the log context object
still in the root's log context list - this happens if 'sync_log' was
set to true before we called btrfs_whiteout_for_rename() and it is
dangerous because we end up with a corrupt linked list (root->log_ctxs)
as the log context object was allocated on the stack.

After btrfs_rename() returns, any task that is running btrfs_sync_log()
concurrently can end up crashing because that linked list is traversed by
btrfs_sync_log() (through btrfs_remove_all_log_ctxs()). That results in
the same issue that commit e6c617102c7e4 ("Btrfs: fix log context list
corruption after rename exchange operation") fixed.

Fixes: d4682ba03ef618 ("Btrfs: sync log after logging new name")
Signed-off-by: Filipe Manana <fdmanana@suse.com>
---
 fs/btrfs/inode.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 3a636b405088..fd9091808ae5 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -9546,6 +9546,10 @@ static int btrfs_rename(struct inode *old_dir, struct dentry *old_dentry,
 		ret = btrfs_sync_log(trans, BTRFS_I(old_inode)->root, &ctx);
 		if (ret)
 			commit_transaction = true;
+	} else if (sync_log) {
+		mutex_lock(&root->log_mutex);
+		list_del(&ctx.list);
+		mutex_unlock(&root->log_mutex);
 	}
 	if (commit_transaction) {
 		ret = btrfs_commit_transaction(trans);
-- 
2.11.0

Re: [PATCH] Btrfs: fix log context list corruption after rename whiteout error

[David Sterba]

On Tue, Mar 10, 2020 at 12:13:53PM +0000, fdmanana@kernel.org wrote:
> From: Filipe Manana <fdmanana@suse.com>
> 
> During a rename whiteout, if btrfs_whiteout_for_rename() returns an error
> we can end up returning from btrfs_rename() with the log context object
> still in the root's log context list - this happens if 'sync_log' was
> set to true before we called btrfs_whiteout_for_rename() and it is
> dangerous because we end up with a corrupt linked list (root->log_ctxs)
> as the log context object was allocated on the stack.
> 
> After btrfs_rename() returns, any task that is running btrfs_sync_log()
> concurrently can end up crashing because that linked list is traversed by
> btrfs_sync_log() (through btrfs_remove_all_log_ctxs()). That results in
> the same issue that commit e6c617102c7e4 ("Btrfs: fix log context list
> corruption after rename exchange operation") fixed.
> 
> Fixes: d4682ba03ef618 ("Btrfs: sync log after logging new name")
> Signed-off-by: Filipe Manana <fdmanana@suse.com>

Added to misc-next, thanks.