Commit ac6f0cb3 authored Apr 15, 2018 by Jiri Olsa Committed by Greg Kroah-Hartman Apr 29, 2018

perf: Fix sample_max_stack maximum check

commit 5af44ca53d019de47efe6dbc4003dd518e5197ed upstream.

The syzbot hit KASAN bug in perf_callchain_store having the entry stored
behind the allocated bounds [1].

We miss the sample_max_stack check for the initial event that allocates
callchain buffers. This missing check allows to create an event with
sample_max_stack value bigger than the global sysctl maximum:

  # sysctl -a | grep perf_event_max_stack
  kernel.perf_event_max_stack = 127

  # perf record -vv -C 1 -e cycles/max-stack=256/ kill
  ...
  perf_event_attr:
    size                             112
    ...
    sample_max_stack                 256
  ------------------------------------------------------------
  sys_perf_event_open: pid -1  cpu 1  group_fd -1  flags 0x8 = 4

Note the '-C 1', which forces perf record to create just single event.
Otherwise it opens event for every cpu, then the sample_max_stack check
fails on the second event and all's fine.

The fix is to run the sample_max_stack check also for the first event
with callchains.

[1] https://marc.info/?l=linux-kernel&m=152352732920874&w=2



Reported-by:  <syzbot+7c449856228b63ac951e@syzkaller.appspotmail.com>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: syzkaller-bugs@googlegroups.com
Cc: x86@kernel.org
Fixes: 97c79a38 ("perf core: Per event callchain limit")
Link: http://lkml.kernel.org/r/20180415092352.12403-2-jolsa@kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent fdc2090b

kernel/events/callchain.c

+12 −9

Original line number	Diff line number	Diff line
		@@ -117,10 +117,6 @@ int get_callchain_buffers(int event_max_stack)
		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
		@@ -128,11 +124,18 @@ int get_callchain_buffers(int event_max_stack)
		*
		* And also do it here so that we have &callchain_mutex held.
		*/
		if (event_max_stack > sysctl_perf_event_max_stack)
		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;
		goto exit;
		}

		err = alloc_callchain_buffers();
		exit:
		if (err)