[v2] Btrfs: fix list transaction->pending_ordered corruption

Commit Message

Filipe Manana July 3, 2015, 9:22 p.m. UTC

From: Filipe Manana <[e-mail]>

When we call btrfs_commit_transaction(), we splice the list "ordered"
of our transaction handle into the transaction's "pending_ordered"
list, but we don't re-initialize the "ordered" list of our transaction
handle, this means it still points to the same elements it used to
before the splice. Then we check if the current transaction's state is
>= TRANS_STATE_COMMIT_START and if it is we end up calling
btrfs_end_transaction() which simply splices again the "ordered" list
of our handle into the transaction's "pending_ordered" list, leaving
multiple pointers to the same ordered extents which results in list
corruption when we are iterating, removing and freeing ordered extents
at btrfs_wait_pending_ordered(), resulting in access to dangling
pointers / use-after-free issues.
Similarly, btrfs_end_transaction() can end up in some cases calling
btrfs_commit_transaction(), and both did a list splice of the transaction
handle's "ordered" list into the transaction's "pending_ordered" without
re-initializing the handle's "ordered" list, resulting in exactly the
same problem.

This produces the following warning on a kernel with linked list
debugging enabled:

[109749.265416] ------------[ cut here ]------------
[109749.266410] WARNING: CPU: 7 PID: 324 at lib/list_debug.c:59 __list_del_entry+0x5a/0x98()
[109749.267969] list_del corruption. prev->next should be ffff8800ba087e20, but was fffffff8c1f7c35d
(...)
[109749.287505] Call Trace:
[109749.288135]  [<ffffffff8145f077>] dump_stack+0x4f/0x7b
[109749.298080]  [<ffffffff81095de5>] ? console_unlock+0x356/0x3a2
[109749.331605]  [<ffffffff8104b3b0>] warn_slowpath_common+0xa1/0xbb
[109749.334849]  [<ffffffff81260642>] ? __list_del_entry+0x5a/0x98
[109749.337093]  [<ffffffff8104b410>] warn_slowpath_fmt+0x46/0x48
[109749.337847]  [<ffffffff81260642>] __list_del_entry+0x5a/0x98
[109749.338678]  [<ffffffffa053e8bf>] btrfs_wait_pending_ordered+0x46/0xdb [btrfs]
[109749.340145]  [<ffffffffa058a65f>] ? __btrfs_run_delayed_items+0x149/0x163 [btrfs]
[109749.348313]  [<ffffffffa054077d>] btrfs_commit_transaction+0x36b/0xa10 [btrfs]
[109749.349745]  [<ffffffff81087310>] ? trace_hardirqs_on+0xd/0xf
[109749.350819]  [<ffffffffa055370d>] btrfs_sync_file+0x36f/0x3fc [btrfs]
[109749.351976]  [<ffffffff8118ec98>] vfs_fsync_range+0x8f/0x9e
[109749.360341]  [<ffffffff8118ecc3>] vfs_fsync+0x1c/0x1e
[109749.368828]  [<ffffffff8118ee1d>] do_fsync+0x34/0x4e
[109749.369790]  [<ffffffff8118f045>] SyS_fsync+0x10/0x14
[109749.370925]  [<ffffffff81465197>] system_call_fastpath+0x12/0x6f
[109749.382274] ---[ end trace 48e0d07f7c03d95a ]---

On a non-debug kernel this leads to invalid memory accesses, causing a
crash. Fix this by using list_splice_init() instead of list_splice() in
btrfs_commit_transaction() and btrfs_end_transaction().

Cc: [e-mail]
Fixes: 50d9aa99bd35 ("Btrfs: make sure logged extents complete in the current transaction V3"
Signed-off-by: Filipe Manana <[e-mail]>
---

V2: Use list_splice_init() in btrfs_end_transaction() too, as it can
    often call btrfs_commit_transaction() and would result in exactly
    the same problem but just in the reverse direction.

 fs/btrfs/transaction.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Comments

David Sterba July 9, 2015, 6 p.m. UTC | #1

On Fri, Jul 03, 2015 at 10:22:08PM +0100, [e-mail] wrote:
> From: Filipe Manana <[e-mail]>
> Cc: [e-mail]
> Fixes: 50d9aa99bd35 ("Btrfs: make sure logged extents complete in the current transaction V3"
> Signed-off-by: Filipe Manana <[e-mail]>

... now for the right patch,

Reviewed-by: David Sterba <[e-mail]>
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Patch

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index c0f18e7..51e0f0d 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -761,7 +761,7 @@  static int __btrfs_end_transaction(struct btrfs_trans_handle *trans,
 
 	if (!list_empty(&trans->ordered)) {
 		spin_lock(&info->trans_lock);
-		list_splice(&trans->ordered, &cur_trans->pending_ordered);
+		list_splice_init(&trans->ordered, &cur_trans->pending_ordered);
 		spin_unlock(&info->trans_lock);
 	}
 
@@ -1866,7 +1866,7 @@  int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
 	}
 
 	spin_lock(&root->fs_info->trans_lock);
-	list_splice(&trans->ordered, &cur_trans->pending_ordered);
+	list_splice_init(&trans->ordered, &cur_trans->pending_ordered);
 	if (cur_trans->state >= TRANS_STATE_COMMIT_START) {
 		spin_unlock(&root->fs_info->trans_lock);
 		atomic_inc(&cur_trans->use_count);