Re: FAILED: patch "[PATCH] bpf: Fix toctou on read-only map's constant scalar tracking" failed to apply to 5.4-stable tree

From: Daniel Borkmann <daniel@iogearbox.net>
To: Lee Jones <lee.jones@linaro.org>,
	Rafael David Tinoco <rafaeldtinoco@gmail.com>
Cc: andrii@kernel.org, ast@kernel.org, stable@vger.kernel.org,
	Greg KH <gregkh@linuxfoundation.org>
Subject: Re: FAILED: patch "[PATCH] bpf: Fix toctou on read-only map's constant scalar tracking" failed to apply to 5.4-stable tree
Date: Tue, 1 Mar 2022 22:23:03 +0100	[thread overview]
Message-ID: <f01b6557-ed8f-1385-c5f6-95f73b940b7f@iogearbox.net> (raw)
In-Reply-To: <YhNtE/sIdv5OkBQT@google.com>

Hi Lee, [ also Cc'ing Rafael, ]

On 2/21/22 11:44 AM, Lee Jones wrote:
> On Mon, 21 Feb 2022, Greg KH wrote:
>> On Mon, Feb 21, 2022 at 09:52:34AM +0000, Lee Jones wrote:
>>> On Thu, 17 Feb 2022, Lee Jones wrote:
>>>> On Thu, 17 Feb 2022, Greg KH wrote:
>>>>> On Thu, Feb 17, 2022 at 03:57:23PM +0000, Lee Jones wrote:
>>>>>> On Mon, 22 Nov 2021, gregkh@linuxfoundation.org wrote:
>>>>>>>
>>>>>>> The patch below does not apply to the 5.4-stable tree.
>>>>>>> If someone wants it applied there, or to any other stable or longterm
>>>>>>> tree, then please email the backport, including the original git commit
>>>>>>> id to <stable@vger.kernel.org>.
>>>>>>
>>>>>> We are in receipt of a bug report which cites this patch as the fix.
>>>>>
>>>>> Does the bug report really say that this issue is present in the 5.4
>>>>> kernel tree?  Anything older?
>>>>
>>>> Not specifically, but the commit referenced in the Fixes tag landed in
>>>> v5.5. and was successfully back-ported to v5.4.144.
>>>
>>> Another potential avenue might to be revert the back-ported commit
>>> which caused the issue from v5.4.y.
>>
>> Unless that was fixing a different issue?  I have no idea at this point
>> what commit you are talking about, sorry :(
> 
> The bad-commit mentioned in "the Fixes tag":
> 
> Fixes: a23740ec43ba ("bpf: Track contents of read-only maps as scalars")
> 
> Which as you say, could well have been fixing another issue.
> 
> In fact, yes it was:
> 
> https://lore.kernel.org/stable/20210821203108.215937-2-rafaeldtinoco@gmail.com/
> 
> Daniel, what do you suggest please?

Hm, okay, so a23740ec43ba ("bpf: Track contents of read-only maps as scalars") was
backported to 5.4.144 given Rafael needed it to fix a failing regression test [0].

Normally, I would have said that we should just revert a23740ec43ba given it was
not a 'fix' in the first place, but then we are getting into a situation where it
would break Rafael's now functioning test case again on 5.4.144+ released kernels.

Rafael, given you need this, do you have some cycles to help out Lee on this backport
for 5.4 stable?

Thanks guys,
Daniel

  [0] https://lore.kernel.org/stable/20210821203108.215937-1-rafaeldtinoco@gmail.com/