linux-kernel - Re: perf: fuzzer KASAN: global-out-of-bounds in match

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Message-ID: <877f81f264.fsf@ashishki-desk.ger.corp.intel.com>
Date:   Fri, 18 Nov 2016 13:38:43 +0200
From:   Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:     Vince Weaver <vincent.weaver@...ne.edu>,
        "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        "dvyukov\@google.com" <dvyukov@...gle.com>
Subject: Re: perf: fuzzer KASAN: global-out-of-bounds in match_token

Vince Weaver <vincent.weaver@...ne.edu> writes:

> On Thu, 17 Nov 2016, Vince Weaver wrote:
>
>> On Thu, 17 Nov 2016, Vince Weaver wrote:
>> > > 
>> > > [  911.507365] ==================================================================
>> > > [  911.514824] BUG: KASAN: global-out-of-bounds in match_token+0x268/0x310 at addr ffffffffb14ad058
>> > > [  911.523912] Read of size 8 by task perf_fuzzer/20662
>> > > [  911.528945] Address belongs to variable if_tokens+0x78/0xa0
>
> I managed to create a short reproducer that reliably causes the issue on 
> my skylake test machine.

Thanks a bunch, and ugh, this is embarrassing.

>From 139306c3bcf7abf49c51a8e56131aaae51222594 Mon Sep 17 00:00:00 2001
From: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Date: Fri, 18 Nov 2016 13:24:55 +0200
Subject: [PATCH] perf: Fix address filter parser

The token table passed into match_token() must be null-terminated, which
it currently is not in the perf's address filter string parser, as caught
by Vince's perf_fuzzer and KASAN. It doesn't blow up otherwise because of
the alignment padding of the table to the next element in the .rodata,
which is luck.

Fixing by adding a null-terminator to the token table.

Signed-off-by: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Fixes: 375637bc524 ("perf/core: Introduce address range filtering")
Reported-by: Vince Weaver <vincent.weaver@...ne.edu>
Cc: stable@...r.kernel.org # v4.7+
---
 kernel/events/core.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index c6e47e97b3..63c72dee71 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -8012,6 +8012,7 @@ static void perf_event_addr_filters_apply(struct perf_event *event)
  * if <size> is not specified, the range is treated as a single address.
  */
 enum {
+	IF_ACT_NONE = -1,
 	IF_ACT_FILTER,
 	IF_ACT_START,
 	IF_ACT_STOP,
@@ -8035,6 +8036,7 @@ static const match_table_t if_tokens = {
 	{ IF_SRC_KERNEL,	"%u/%u" },
 	{ IF_SRC_FILEADDR,	"%u@%s" },
 	{ IF_SRC_KERNELADDR,	"%u" },
+	{ IF_ACT_NONE,		NULL },
 };
 
 /*
-- 
2.10.2