[PATCH] Btrfs: fix qgroup double free after failure to reserve metadata for delalloc

[PATCH] Btrfs: fix qgroup double free after failure to reserve metadata for delalloc

[fdmanana]

From: Filipe Manana <fdmanana@suse.com>

If we fail to reserve metadata for delalloc operations we end up releasing
the previously reserved qgroup amount twice, once explicitly under the
'out_qgroup' label by calling btrfs_qgroup_free_meta_prealloc() and once
again, under label 'out_fail', by calling btrfs_inode_rsv_release() with a
value of 'true' for its 'qgroup_free' argument, which results in
btrfs_qgroup_free_meta_prealloc() being called again, so we end up having
a double free.

Also if we fail to reserve the necessary qgroup amount, we jump to the
label 'out_fail', which calls btrfs_inode_rsv_release() and that in turns
calls btrfs_qgroup_free_meta_prealloc(), even though we weren't able to
reserve any qgroup amount. So we freed some amount we never reserved.

So fix this by removing the call to btrfs_inode_rsv_release() in the
failure path, since it's not necessary at all as we haven't changed the
inode's block reserve in any way at this point.

Fixes: c8eaeac7b73434 ("btrfs: reserve delalloc metadata differently")
Signed-off-by: Filipe Manana <fdmanana@suse.com>
---
 fs/btrfs/delalloc-space.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/fs/btrfs/delalloc-space.c b/fs/btrfs/delalloc-space.c
index d949d7d2abed..fe68d0e078bd 100644
--- a/fs/btrfs/delalloc-space.c
+++ b/fs/btrfs/delalloc-space.c
@@ -381,7 +381,6 @@ int btrfs_delalloc_reserve_metadata(struct btrfs_inode *inode, u64 num_bytes)
 out_qgroup:
 	btrfs_qgroup_free_meta_prealloc(root, qgroup_reserve);
 out_fail:
-	btrfs_inode_rsv_release(inode, true);
 	if (delalloc_lock)
 		mutex_unlock(&inode->delalloc_mutex);
 	return ret;
-- 
2.11.0

Re: [PATCH] Btrfs: fix qgroup double free after failure to reserve metadata for delalloc

[David Sterba]

On Tue, Oct 15, 2019 at 10:54:39AM +0100, fdmanana@kernel.org wrote:
> From: Filipe Manana <fdmanana@suse.com>
> 
> If we fail to reserve metadata for delalloc operations we end up releasing
> the previously reserved qgroup amount twice, once explicitly under the
> 'out_qgroup' label by calling btrfs_qgroup_free_meta_prealloc() and once
> again, under label 'out_fail', by calling btrfs_inode_rsv_release() with a
> value of 'true' for its 'qgroup_free' argument, which results in
> btrfs_qgroup_free_meta_prealloc() being called again, so we end up having
> a double free.
> 
> Also if we fail to reserve the necessary qgroup amount, we jump to the
> label 'out_fail', which calls btrfs_inode_rsv_release() and that in turns
> calls btrfs_qgroup_free_meta_prealloc(), even though we weren't able to
> reserve any qgroup amount. So we freed some amount we never reserved.
> 
> So fix this by removing the call to btrfs_inode_rsv_release() in the
> failure path, since it's not necessary at all as we haven't changed the
> inode's block reserve in any way at this point.
> 
> Fixes: c8eaeac7b73434 ("btrfs: reserve delalloc metadata differently")
> Signed-off-by: Filipe Manana <fdmanana@suse.com>

Thanks, added to 5.4-rc queue.