lkml.org 
[lkml]   [2018]   [Jan]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH 08/11] signal/arm: Document conflicts with SI_USER and SIGFPE
Russell King - ARM Linux <linux@armlinux.org.uk> writes:

> On Thu, Jan 11, 2018 at 06:59:37PM -0600, Eric W. Biederman wrote:
>> Setting si_code to 0 results in a userspace seeing an si_code of 0.
>> This is the same si_code as SI_USER. Posix and common sense requires
>> that SI_USER not be a signal specific si_code. As such this use of 0
>> for the si_code is a pretty horribly broken ABI.
>>
>> Further use of si_code == 0 guaranteed that copy_siginfo_to_user saw a
>> value of __SI_KILL and now sees a value of SIL_KILL with the result
>> that uid and pid fields are copied and which might copying the si_addr
>> field by accident but certainly not by design. Making this a very
>> flakey implementation.
>>
>> Utilizing FPE_FIXME, siginfo_layout will now return SIL_FAULT and the
>> appropriate fields will be reliably copied.
>
> So what do you suggest when none of the SIGFPE FPE_xxx codes match the
> condition that "we don't know what happened" ? Raise a SIGKILL instead
> maybe? We will have dumped the VFP state into the kernel log at this
> point, things are pretty much fscked.
>
> It's probably an impossible condition unless the hardware has failed,
> no one has knowingly reported getting such a dump in their kernel log,
> so it's something that could very likely be changed in some way
> without anyone noticing.

It sounds like we have two equally valid possible solutions:
1) force_sig(SIGKILL, current);
2) Allocate a new FPE_xxx code in asm-generic/siginfo.h
I believe the next available number is 15.

If no one is going to notice this should be comparatively easy to fix.
I just don't have the knowledge of arm to make the judgement myself.

Eric

\
 
 \ /
  Last update: 2018-01-15 21:14    [W:0.085 / U:4.344 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site