From: Yu Kuai <yukuai3@huawei.com>

Commit 64dc8c732f5c ("block, bfq: fix possible uaf for 'bfqq->bic'")
will access 'bic->bfqq' in bic_set_bfqq(), however, bfq_exit_icq_bfqq()
can free bfqq first, and then call bic_set_bfqq(), which will cause uaf.

Fix the problem by moving bfq_exit_bfqq() behind bic_set_bfqq().

Fixes: 64dc8c732f5c ("block, bfq: fix possible uaf for 'bfqq->bic'")
Reported-by: Yi Zhang <yi.zhang@redhat.com>
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
---
 block/bfq-iosched.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 16f43bbc575a..ccf2204477a5 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -5317,8 +5317,8 @@ static void bfq_exit_icq_bfqq(struct bfq_io_cq *bic, bool is_sync)
 		unsigned long flags;
 
 		spin_lock_irqsave(&bfqd->lock, flags);
-		bfq_exit_bfqq(bfqd, bfqq);
 		bic_set_bfqq(bic, NULL, is_sync);
+		bfq_exit_bfqq(bfqd, bfqq);
 		spin_unlock_irqrestore(&bfqd->lock, flags);
 	}
 }
-- 
2.31.1

On Mon 26-12-22 11:06:05, Yu Kuai wrote:
> From: Yu Kuai <yukuai3@huawei.com>
> 
> Commit 64dc8c732f5c ("block, bfq: fix possible uaf for 'bfqq->bic'")
> will access 'bic->bfqq' in bic_set_bfqq(), however, bfq_exit_icq_bfqq()
> can free bfqq first, and then call bic_set_bfqq(), which will cause uaf.
> 
> Fix the problem by moving bfq_exit_bfqq() behind bic_set_bfqq().
> 
> Fixes: 64dc8c732f5c ("block, bfq: fix possible uaf for 'bfqq->bic'")
> Reported-by: Yi Zhang <yi.zhang@redhat.com>
> Signed-off-by: Yu Kuai <yukuai3@huawei.com>

Thanks for the patch! Feel free to add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> ---
>  block/bfq-iosched.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
> index 16f43bbc575a..ccf2204477a5 100644
> --- a/block/bfq-iosched.c
> +++ b/block/bfq-iosched.c
> @@ -5317,8 +5317,8 @@ static void bfq_exit_icq_bfqq(struct bfq_io_cq *bic, bool is_sync)
>  		unsigned long flags;
>  
>  		spin_lock_irqsave(&bfqd->lock, flags);
> -		bfq_exit_bfqq(bfqd, bfqq);
>  		bic_set_bfqq(bic, NULL, is_sync);
> +		bfq_exit_bfqq(bfqd, bfqq);
>  		spin_unlock_irqrestore(&bfqd->lock, flags);
>  	}
>  }
> -- 
> 2.31.1
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

On Mon, 26 Dec 2022 11:06:05 +0800, Yu Kuai wrote:
> Commit 64dc8c732f5c ("block, bfq: fix possible uaf for 'bfqq->bic'")
> will access 'bic->bfqq' in bic_set_bfqq(), however, bfq_exit_icq_bfqq()
> can free bfqq first, and then call bic_set_bfqq(), which will cause uaf.
> 
> Fix the problem by moving bfq_exit_bfqq() behind bic_set_bfqq().
> 
> 
> [...]

Applied, thanks!

[1/1] block, bfq: fix uaf for bfqq in bfq_exit_icq_bfqq
      commit: 246cf66e300b76099b5dbd3fdd39e9a5dbc53f02

Best regards,
-- 
Jens Axboe