lkml.org 
[lkml]   [2014]   [Apr]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [perf] more perf_fuzzer memory corruption
On Tue, 15 Apr 2014, Thomas Gleixner wrote:

> On Tue, 15 Apr 2014, Vince Weaver wrote:
> >
> > Still tracking memory corruption bugs found by the perf_fuzzer, I have
> > about 10 different log splats that I think might all be related to the
> > same underlying problem.
> >
> > Anyway I managed to trigger this using the perf_fuzzer:
> >
> > [ 221.065278] Slab corruption (Not tainted): kmalloc-2048 start=ffff8800cd15e800, len=2048
> > [ 221.074062] 040: 6b 6b 6b 6b 6b 6b 6b 6b 98 72 57 cd 00 88 ff ff kkkkkkkk.rW.....
> > [ 221.082321] Prev obj: start=ffff8800cd15e000, len=2048
> > [ 221.087933] 000: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
> > [ 221.096224] 010: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
> >
> > And luckily I had ftrace running at the time.
> >
> > The allocation of this block is by perf_event
> >
> > perf_fuzzer-2520 [001] 182.980563: kmalloc: (perf_event_alloc+0x55) call_site=ffffffff811399b5 ptr=0xffff8800cd15e800 bytes_req=1272 bytes_alloc=2048 gfp_flags=GFP_KERNEL|GFP_ZERO
> > perf_fuzzer-2520 [000] 183.628515: kmalloc: (perf_event_alloc+0x55) call_site=ffffffff811399b5 ptr=0xffff8800cd15e800 bytes_req=1272 bytes_alloc=2048 gfp_flags=GFP_KERNEL|GFP_ZERO
> > perf_fuzzer-2520 [000] 183.628521: kfree: (perf_event_alloc+0x2f7) call_site=ffffffff81139c57 ptr=0xffff8800cd15e800
> > perf_fuzzer-2520 [000] 183.628844: kmalloc: (perf_event_alloc+0x55) call_site=ffffffff811399b5 ptr=0xffff8800cd15e800 bytes_req=1272 bytes_alloc=2048 gfp_flags=GFP_KERNEL|GFP_ZERO
> > ...(thousands of times of kmalloc/kfree)
> >
> > Is it worth wading through this mess to try to track down what happened?
>
> Definitely worth a try. Can you upload the trace file and provide the
> URL or send it offlist in private mail if you cannot provide a public URL.

I've poked around the trace a bit.

Possibly it looks like a struct perf_event is being used after freed,
specifically the event->migrate_entry->prev value? I could
be completely wrong about that.

One thing to know about these fuzzer runs, the ones that cause memory
corruption involve forking (with events active). I haven't seen the
corruptions when forking is disabled.

It's very simple forking, only one child is ever active at a time,
and the child itself doesn't do anything but busy wait until it is killed.

The trace shows the problem allocations happening before a fork and
the poison message after. The traces I have don't include the children
though so I don't have records of what happened there.

I'll send a private link to the file downloads as they're a little large
and the local sysadmins would probably appreicate if I limited access to
them.

Vince


\
 
 \ /
  Last update: 2014-04-16 08:01    [W:0.096 / U:10.288 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site