4.16-stable review patch. If anyone has any objections, please let me know.
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From: Jiri Olsa jolsa@kernel.org
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: 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@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- kernel/events/callchain.c | 21 ++++++++++++--------- 1 file changed, 12 insertions(+), 9 deletions(-)
--- a/kernel/events/callchain.c +++ b/kernel/events/callchain.c @@ -119,19 +119,22 @@ int get_callchain_buffers(int event_max_ 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; }