Re: FAILED: patch "[PATCH] signal: Don't always set SA_IMMUTABLE for forced signals" failed to apply to 5.15-stable tree

From: Thomas Backlund <tmb@iki.fi>
To: ebiederm@xmission.com, Thomas Backlund <tmb@iki.fi>
Cc: Greg KH <gregkh@linuxfoundation.org>,
	keescook@chromium.org, khuey@kylehuey.com, me@kylehuey.com,
	oliver.sang@intel.com, torvalds@linux-foundation.org,
	stable@vger.kernel.org
Subject: Re: FAILED: patch "[PATCH] signal: Don't always set SA_IMMUTABLE for forced signals" failed to apply to 5.15-stable tree
Date: Tue, 23 Nov 2021 23:56:31 +0200	[thread overview]
Message-ID: <2406f6cc-3c24-4b0c-20db-194da63640c7@iki.fi> (raw)
In-Reply-To: <87k0gyim6z.fsf@email.froward.int.ebiederm.org>

Den 2021-11-23 kl. 23:41, skrev ebiederm@xmission.com:
> Thomas Backlund <tmb@iki.fi> writes:
>
>> Den 2021-11-23 kl. 21:24, skrev ebiederm@xmission.com:

>>> Maybe I am wrong but I think "Don't always set SA_IMMUTABLE for forced
>>> signals" will apply if you drop the hunk modifying force_fatal_sig.
>>> Then you don't need to backport all of the cleanups just the fix.
>>>
>>> I will take a quick look and verify that.
>>
>> that's why i wrote: "if the other patch for signal that has similar
>> description should land"
> Apologies for not responding to that bit, I was reading quickly
> and I missed that bit.

No worries :)

> The second patch does not need to land in 5.15.
>> (meaning "signal: Replace force_fatal_sig with force_exit_sig when in
>> doubt")
>>
>> as thats the one needing the whole patch series...
>>
>>
>> since going by patch descriptions for:
>>
>> "signal: Don't always set SA_IMMUTABLE for forced signals"
>>
>> "signal: Replace force_fatal_sig with force_exit_sig when in doubt"
>>
>>
>> both has the info:
>>
>> "Unfortunately this broke debuggers[1][2] which reasonably expect
>> to be able to trap synchronous SIGTRAP and SIGSEGV even when
>> the target process is not configured to handle those signals."
>>
>> and the second even has:
>> "This avoids userspace regressions as older kernels exited with do_exit
>> which debuggers also can not intercept."
>>
>>
>> or is the patch description on the second patch somewhat misleading ?
> It is the same problem.  But it only applies to code that was merged
> post 5.15.
>
> For 5.15 on force_sig_seccomp is really affected.
>
> For 5.16 there were many calls to do_exit that I turned into signals.
> Some of the properly should be oridinary signals and some of them
> for correctness purposes can't allow debuggers or userspace to intercept
> them.
>
> The second patch went through and modified everything that was
> non-interceptible before 5.16 to be non-interceptible in 5.16.  Where
> that is not necessary we can relax things later.
>
> But for 5.15 only the one patch needs to be applied.
>
> Eric

Thanks for the explanation.

--

Thomas