Re: BUG: KASAN: slab-out-of-bounds in perf_callchain_user+0x494/0x530

[Namhyung Kim]

Hello,

On Thu, Nov 30, 2017 at 04:37:12PM -0300, Arnaldo Carvalho de Melo wrote:
> Em Thu, Nov 30, 2017 at 09:20:26AM +0100, Peter Zijlstra escreveu:
> > On Thu, Nov 30, 2017 at 10:32:19AM +0800, Fengguang Wu wrote:
> > > Hello,
> > > 
> > > FYI this happens in mainline kernel 4.15.0-rc1.
> > > It looks like a new regression and hard to bisect.
> > > 
> > > It occurs in 1 out of 57 boots.
> > > 
> > > [   10.009610] chown (367) used greatest stack depth: 26944 bytes left
> > > Kernel tests: Boot OK!
> > > [   30.357729] trinity-main uses obsolete (PF_INET,SOCK_PACKET)
> > > [   31.301433] sock: process `trinity-main' is using obsolete setsockopt SO_BSDCOMPAT
> > > [   31.310289] ==================================================================
> > > [   31.311490] BUG: KASAN: slab-out-of-bounds in perf_callchain_user+0x494/0x530:
> > > 						perf_callchain_store at include/linux/perf_event.h:1128
> > > 						 (inlined by) perf_callchain_user at arch/x86/events/core.c:2485
> > 
> > I don't think we recently changed anything here...
> > 
> > But I do have vague memories of something being off here; I never quite
> > could penetrate the max_stack / contexts_maxed stuff, and istr acme was
> > going to have a peek.
>  
> Sure, but I saw some backward ring buffer stuff in there as well, no?
> IIRC that came after the max-stack code, Adding Wang to the CC list.

I think it's because of per-event max-stack not being checked for the
first event.  Please see the patch below..

Also I'm not sure that the allocation failure check would work
correctly since it decrements nr_callchain_events when it fails.

Thanks,
Namhyung