linux-kernel - [PATCH 07/17] perf: Fix sample_max

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Date:   Fri, 20 Apr 2018 11:32:17 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Clark Williams <williams@...hat.com>, linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org, Jiri Olsa <jolsa@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Andi Kleen <andi@...stfloor.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        syzkaller-bugs@...glegroups.com, x86@...nel.org,
        Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: [PATCH 07/17] perf: Fix sample_max_stack maximum check

From: Jiri Olsa <jolsa@...nel.org>

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@...kaller.appspotmail.com
Signed-off-by: Jiri Olsa <jolsa@...nel.org>
Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: Andi Kleen <andi@...stfloor.org>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: syzkaller-bugs@...glegroups.com
Cc: x86@...nel.org
Fixes: 97c79a38cd45 ("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@...hat.com>
---
 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 772a43fea825..73cc26e321de 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;
 	}
 
-- 
2.14.3