[PATCH] btrfs: relocation: set trans to be NULL after free

[PATCH] btrfs: relocation: set trans to be NULL after free

[Pan Bian]

The function relocate_block_group calls btrfs_end_transaction to release
trans when update_backref_cache returns 1, and then continues the loop
body. If btrfs_block_rsv_refill fails this time, it will jump out the
loop and the freed trans will be accessed. This may result in a
use-after-free bug. The patch assigns NULL to trans after trans is
released so that it will not be accessed.

Fixes: 0647bf564f1("Btrfs: improve forever loop when doing balance
relocation")

Signed-off-by: Pan Bian <bianpan2016@163.com>
---
 fs/btrfs/relocation.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index 924116f..a3f75b8 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -3959,6 +3959,7 @@ static noinline_for_stack int relocate_block_group(struct reloc_control *rc)
 restart:
 		if (update_backref_cache(trans, &rc->backref_cache)) {
 			btrfs_end_transaction(trans);
+			trans = NULL;
 			continue;
 		}
 
-- 
2.7.4

Re: [PATCH] btrfs: relocation: set trans to be NULL after free

[Qu Wenruo]

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On 2018/11/23 下午6:10, Pan Bian wrote:
> The function relocate_block_group calls btrfs_end_transaction to release
> trans when update_backref_cache returns 1, and then continues the loop
> body. If btrfs_block_rsv_refill fails this time, it will jump out the
> loop and the freed trans will be accessed. This may result in a
> use-after-free bug. The patch assigns NULL to trans after trans is
> released so that it will not be accessed.
> 
> Fixes: 0647bf564f1("Btrfs: improve forever loop when doing balance
> relocation")
> 
> Signed-off-by: Pan Bian <bianpan2016@163.com>

Reviewed-by: Qu Wenruo <wqu@suse.com>

Thanks,
Qu

> ---
>  fs/btrfs/relocation.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
> index 924116f..a3f75b8 100644
> --- a/fs/btrfs/relocation.c
> +++ b/fs/btrfs/relocation.c
> @@ -3959,6 +3959,7 @@ static noinline_for_stack int relocate_block_group(struct reloc_control *rc)
>  restart:
>  		if (update_backref_cache(trans, &rc->backref_cache)) {
>  			btrfs_end_transaction(trans);
> +			trans = NULL;
>  			continue;
>  		}
>  
> 


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Re: [PATCH] btrfs: relocation: set trans to be NULL after free

[David Sterba]

On Fri, Nov 23, 2018 at 06:10:15PM +0800, Pan Bian wrote:
> The function relocate_block_group calls btrfs_end_transaction to release
> trans when update_backref_cache returns 1, and then continues the loop
> body. If btrfs_block_rsv_refill fails this time, it will jump out the
> loop and the freed trans will be accessed. This may result in a
> use-after-free bug. The patch assigns NULL to trans after trans is
> released so that it will not be accessed.
> 
> Fixes: 0647bf564f1("Btrfs: improve forever loop when doing balance
> relocation")
> 
> Signed-off-by: Pan Bian <bianpan2016@163.com>

Good catch, thanks.

Reviewed-by: David Sterba <dsterba@suse.com>