Messages in this thread | | | From | Dmitry Vyukov <> | Date | Tue, 6 Sep 2016 17:18:56 +0200 | Subject | Re: perf: out-of-bounds write in perf_callchain_store |
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On Tue, Sep 6, 2016 at 5:05 PM, Arnaldo Carvalho de Melo <acme@kernel.org> wrote: > Em Tue, Sep 06, 2016 at 04:49:29PM +0200, Dmitry Vyukov escreveu: >> On Tue, Sep 6, 2016 at 4:44 PM, Arnaldo Carvalho de Melo >> <acme@kernel.org> wrote: >> > Em Tue, Sep 06, 2016 at 04:36:08PM +0200, Peter Zijlstra escreveu: >> >> On Tue, Sep 06, 2016 at 03:42:40PM +0200, Dmitry Vyukov wrote: >> >> > Hello, >> >> > >> >> > The following program trigger an out-of-bounds write in >> >> > perf_callchain_store (if run in a parallel loop): >> >> > >> >> > https://gist.githubusercontent.com/dvyukov/c05d883e776a353a1d063b670f50bde6/raw/1c8906b1aacfbd8a0cc0b5cf0cc4d0535345e497/gistfile1.txt >> >> > >> >> > >> >> > BUG: KASAN: slab-out-of-bounds in perf_callchain_user+0xe65/0xfc0 at >> >> > addr ffff88003e162840 >> >> > Write of size 8 by task syz-executor/22516 >> >> > CPU: 0 PID: 22516 Comm: syz-executor Not tainted 4.8.0-rc5-next-20160905+ #14 >> >> > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 >> >> > ffffffff886b6fe0 ffff88003ec07738 ffffffff82db81a9 ffffffff00000000 >> >> > fffffbfff10d6dfc ffff88003e800a00 ffff88003e161740 ffff88003e163740 >> >> > 0000000000000001 ffff88003e162840 ffff88003ec07760 ffffffff8180b2ec >> >> > Call Trace: >> >> > [<ffffffff8180b9c7>] __asan_report_store8_noabort+0x17/0x20 >> >> > mm/kasan/report.c:332 >> >> > [< inline >] perf_callchain_store include/linux/perf_event.h:1146 >> >> > [<ffffffff81014925>] perf_callchain_user+0xe65/0xfc0 arch/x86/events/core.c:2441 >> >> > [<ffffffff816c5f48>] get_perf_callchain+0x448/0x680 kernel/events/callchain.c:235 >> >> > [<ffffffff816c62cd>] perf_callchain+0x14d/0x1a0 kernel/events/callchain.c:191 >> >> >> >> Urgh, that callchain code is a pain with that context/entries >> >> separation. But I can't see an obvious overrun there. >> >> >> >> But WTF is max_contexts a sysctl? that doesn't seen to make any kind of >> >> sense. >> >> >> >> Acme, can you untangle that stuff and spot the fail? >> > >> > I looked at it briefly some moments ago, couldn't find it so far, have >> > to look at what was behind adding a sysctl for that :-\ >> > >> > And yeah, that entry/ctx thing, IIRC, was done to reduce patch size, >> > probably needs some polishing to become clearer. >> >> >> I believe fuzzer wasn't messing with sysctl's. >> But, yeah, I guess it's really bad idea to try to change them on a >> running system. > > Why? They start with a reasonable value, but that is not ok for all > cases, thus they were introduced, and they only can get changed if there > are _no_ callchain users, so what would be the problem?
Sorry, I missed the "they only can get changed if there are _no_ callchain users" part.
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