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

[Arnaldo Carvalho de Melo]

Em Tue, Dec 05, 2017 at 05:11:56PM +0900, Namhyung Kim escreveu:
> 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..

Argh, well spotted,

Acked-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
 
> Also I'm not sure that the allocation failure check would work
> correctly since it decrements nr_callchain_events when it fails.

Can you elaborate a bit more?
 
> Thanks,
> Namhyung
> 
> 
> 
> >From c12126c4ff9835f0899619db3ee7b4a3151ff2bb Mon Sep 17 00:00:00 2001
> From: Namhyung Kim <namhyung@xxxxxxxxxx>
> Date: Tue, 5 Dec 2017 16:54:50 +0900
> Subject: [PATCH] perf/core: Fix overflow on perf_callchain_entry
> 
> The commit 97c79a38cd45 add a check whether per-event max stack is
> greater than the global max.  But it missed to do it for the first
> event.  So if the event had a stack depth greater than the global max,
> it could overflow the callchain entry list.
> 
> Reported-by: Fengguang Wu <fengguang.wu@xxxxxxxxx>
> Fixes: 97c79a38cd45 ("perf core: Per event callchain limit")
> Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>
> ---
>  kernel/events/callchain.c | 21 ++++++++++++---------
>  1 file changed, 12 insertions(+), 9 deletions(-)
> 
> diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c
> index 1b2be63c8528..e449e23802eb 100644
> --- a/kernel/events/callchain.c
> +++ b/kernel/events/callchain.c
> @@ -119,19 +119,22 @@ int get_callchain_buffers(int event_max_stack)
>  		goto exit;
>  	}
>  
> +	/*
> +	 * If requesting per event more than the global cap,
> +	 * return a different error to help userspace figure this out.
> +	 *
> +	 * And also do it here so that we have &callchain_mutex held.
> +	 */
> +	if (event_max_stack > sysctl_perf_event_max_stack) {
> +		err = -EOVERFLOW;
> +		goto exit;
> +	}
> +
>  	if (count > 1) {
>  		/* If the allocation failed, give up */
>  		if (!callchain_cpus_entries)
>  			err = -ENOMEM;
> -		/*
> -		 * If requesting per event more than the global cap,
> -		 * return a different error to help userspace figure
> -		 * this out.
> -		 *
> -		 * And also do it here so that we have &callchain_mutex held.
> -		 */
> -		if (event_max_stack > sysctl_perf_event_max_stack)
> -			err = -EOVERFLOW;
> +
>  		goto exit;
>  	}
>  
> -- 
> 2.15.0