Re: Patch "bpf: Fix off-by-one in tail call count limiting" has been added to the 5.14-stable tree

[Daniel Borkmann <daniel@iogearbox.net>]

Hi Sasha,

On 9/16/21 1:31 PM, Sasha Levin wrote:
> This is a note to let you know that I've just added the patch titled
> 
>      bpf: Fix off-by-one in tail call count limiting
> 
> to the 5.14-stable tree which can be found at:
>      http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
> 
> The filename of the patch is:
>       bpf-fix-off-by-one-in-tail-call-count-limiting.patch
> and it can be found in the queue-5.14 subdirectory.
> 
> If you, or anyone else, feels it should not be added to the stable tree,
> please let <stable@vger.kernel.org> know about it.
> 
> commit 0af0fa0371eb376731a350bfdd8687e7ec206bb9
> Author: Johan Almbladh <johan.almbladh@anyfinetworks.com>
> Date:   Wed Jul 28 18:47:41 2021 +0200
> 
>      bpf: Fix off-by-one in tail call count limiting
>      
>      [ Upstream commit b61a28cf11d61f512172e673b8f8c4a6c789b425 ]

Please either drop this commit from stable queues, or also queue its revert as
well (in case you don't have a filter in place, and there's a chance this could
get re-queued again in future by accident):

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=f9dabe016b63c9629e152bf876c126c29de223cb

>      Before, the interpreter allowed up to MAX_TAIL_CALL_CNT + 1 tail calls.
>      Now precisely MAX_TAIL_CALL_CNT is allowed, which is in line with the
>      behavior of the x86 JITs.
>      
>      Signed-off-by: Johan Almbladh <johan.almbladh@anyfinetworks.com>
>      Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
>      Acked-by: Yonghong Song <yhs@fb.com>
>      Link: https://lore.kernel.org/bpf/20210728164741.350370-1-johan.almbladh@anyfinetworks.com
>      Signed-off-by: Sasha Levin <sashal@kernel.org>
> 
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index 0a28a8095d3e..82af6279992d 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -1564,7 +1564,7 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn)
>   
>   		if (unlikely(index >= array->map.max_entries))
>   			goto out;
> -		if (unlikely(tail_call_cnt > MAX_TAIL_CALL_CNT))
> +		if (unlikely(tail_call_cnt >= MAX_TAIL_CALL_CNT))
>   			goto out;
>   
>   		tail_call_cnt++;
> 

Thanks,
Daniel