Messages in this thread | | | From | Dmitry Vyukov <> | Date | Mon, 7 Dec 2015 12:24:12 +0100 | Subject | Re: use-after-free in __perf_install_in_context |
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On Mon, Dec 7, 2015 at 12:06 PM, Dmitry Vyukov <dvyukov@google.com> wrote: > On Mon, Dec 7, 2015 at 12:04 PM, Dmitry Vyukov <dvyukov@google.com> wrote: >> On Fri, Dec 4, 2015 at 10:00 PM, Dmitry Vyukov <dvyukov@google.com> wrote: >>> On Fri, Dec 4, 2015 at 9:32 PM, Alexei Starovoitov >>> <alexei.starovoitov@gmail.com> wrote: >>>> On Fri, Dec 04, 2015 at 09:04:35PM +0100, Dmitry Vyukov wrote: >>>>> Hello, >>>>> >>>>> While running syzkaller fuzzer I am seeing lots of the following >>>>> use-after-free reports. Unfortunately all my numerous attempts to >>>>> reproduce them in a controlled environment failed. They pop up during >>>>> fuzzing periodically (once in several hours in a single VM), but >>>>> whenever I try to stress-replay what happened in the VM before the >>>>> report, the use-after-free does not reproduce. Can somebody >>>>> knowledgeable in perf subsystem look at the report? Maybe it is >>>>> possible to figure out what happened based purely on the report. I can >>>>> pretty reliably test any proposed fixes. >>>>> All reports look like this one. Then it is usually followed by other >>>>> reports and eventually kernel hangs or dies. What happens in the >>>>> fuzzer is essentially random syscalls with random arguments, tasks >>>>> born and die concurrently and so on. I was able to reproduce it by >>>>> restricting syscalls only to perf_event_open, perf ioctls and bpf >>>>> syscall. >>>> >>>> For the sake of trying to narrow it down: >>>> does the error disappear when you stop using bpf syscall in your fuzzing? >>>> If yes, then I could have missed some interaction between perf_event_free, >>>> kprobe free and bpf_prog_free. >>>> There was a race there before. >>>> May be there is still something else. >>> >>> >>> It is a good question. I will test it. >> >> >> Testing without bpf, so far hit the following warning on a non-tainted kernel: >> >> >> ------------[ cut here ]------------ >> WARNING: CPU: 0 PID: 26259 at kernel/events/core.c:2696 >> task_ctx_sched_out+0x12c/0x1c0() >> Modules linked in: >> CPU: 0 PID: 26259 Comm: syzkaller_execu Not tainted 4.4.0-rc3+ #150 >> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 >> 0000000000000000 ffff88006579f9a8 ffffffff82c6f2a8 0000000041b58ab3 >> ffffffff8788bf8d ffffffff82c6f1f6 ffff88003dd32d00 ffff88003469b9c0 >> ffffffff81626130 ffff88006579fa10 0000000000000000 0000000000006693 >> Call Trace: >> [< inline >] __dump_stack lib/dump_stack.c:15 >> [<ffffffff82c6f2a8>] dump_stack+0xb2/0xfa lib/dump_stack.c:50 >> [<ffffffff812ca446>] warn_slowpath_common+0xe6/0x170 kernel/panic.c:460 >> [<ffffffff812ca699>] warn_slowpath_null+0x29/0x30 kernel/panic.c:493 >> [<ffffffff8163302c>] task_ctx_sched_out+0x12c/0x1c0 kernel/events/core.c:2696 >> [< inline >] perf_event_exit_task_context kernel/events/core.c:8815 >> [<ffffffff8165669a>] perf_event_exit_task+0x27a/0xae0 kernel/events/core.c:8881 >> [<ffffffff812d4a12>] do_exit+0x892/0x3050 kernel/exit.c:759 >> [<ffffffff812d732c>] do_group_exit+0xec/0x390 kernel/exit.c:880 >> [<ffffffff81302177>] get_signal+0x677/0x1bf0 kernel/signal.c:2307 >> [<ffffffff8118645e>] do_signal+0x7e/0x2170 arch/x86/kernel/signal.c:709 >> [<ffffffff81003a1e>] exit_to_usermode_loop+0xfe/0x1e0 >> arch/x86/entry/common.c:247 >> [< inline >] prepare_exit_to_usermode arch/x86/entry/common.c:282 >> [<ffffffff8100733b>] syscall_return_slowpath+0x16b/0x240 >> arch/x86/entry/common.c:344 >> [<ffffffff868dafe2>] int_ret_from_sys_call+0x25/0x9f >> arch/x86/entry/entry_64.S:281 >> ---[ end trace c5e9cee9f12b7d5f ]--- >> >> >> >> static void task_ctx_sched_out(struct perf_event_context *ctx) >> { >> struct perf_cpu_context *cpuctx = __get_cpu_context(ctx); >> >> if (!cpuctx->task_ctx) >> return; >> >> if (WARN_ON_ONCE(ctx != cpuctx->task_ctx)) >> return; >> >> ctx_sched_out(ctx, cpuctx, EVENT_ALL); >> cpuctx->task_ctx = NULL; >> } > > > > Also this one. I saw them regularly, but I though that they are > induced by the use-after-frees, but now I see them on a non-tainted > kernel: > > > ------------[ cut here ]------------ > WARNING: CPU: 1 PID: 25357 at arch/x86/kernel/hw_breakpoint.c:160 > arch_uninstall_hw_breakpoint+0x1e1/0x2a0() > Can't find any breakpoint slot > Modules linked in: > CPU: 1 PID: 25357 Comm: syzkaller_execu Not tainted 4.4.0-rc3+ #150 > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 > 0000000000000001 ffff8800333c74e8 ffffffff82c6f2a8 0000000041b58ab3 > ffffffff8788bf8d ffffffff82c6f1f6 ffffffff8696a5e0 ffff8800333c7560 > ffffffff8696a620 00000000000000a0 0000000000000009 ffff8800333c74c8 > Call Trace: > [< inline >] __dump_stack lib/dump_stack.c:15 > [<ffffffff82c6f2a8>] dump_stack+0xb2/0xfa lib/dump_stack.c:50 > [<ffffffff812ca446>] warn_slowpath_common+0xe6/0x170 kernel/panic.c:460 > [<ffffffff812ca579>] warn_slowpath_fmt+0xa9/0xd0 kernel/panic.c:472 > [<ffffffff811a1c31>] arch_uninstall_hw_breakpoint+0x1e1/0x2a0 > arch/x86/kernel/hw_breakpoint.c:160 > [<ffffffff8165e1b5>] hw_breakpoint_del+0x15/0x20 > kernel/events/hw_breakpoint.c:595 > [<ffffffff81631aa4>] event_sched_out+0x704/0x1270 kernel/events/core.c:1580 > [<ffffffff81632681>] group_sched_out+0x71/0x1f0 kernel/events/core.c:1606 > [<ffffffff81632d02>] ctx_sched_out+0x502/0x700 kernel/events/core.c:2414 > [< inline >] perf_event_context_sched_out kernel/events/core.c:2593 > [<ffffffff81645524>] __perf_event_task_sched_out+0x4d4/0x1800 > kernel/events/core.c:2678 > [< inline >] perf_event_task_sched_out include/linux/perf_event.h:946 > [< inline >] prepare_task_switch kernel/sched/core.c:2489 > [< inline >] context_switch kernel/sched/core.c:2647 > [<ffffffff868c986f>] __schedule+0xa0f/0x1f40 kernel/sched/core.c:3156 > [<ffffffff868cae0d>] schedule+0x6d/0x210 kernel/sched/core.c:3185 > [< inline >] freezable_schedule include/linux/freezer.h:171 > [<ffffffff814c09c6>] futex_wait_queue_me+0x306/0x680 kernel/futex.c:2188 > [<ffffffff814c238c>] futex_wait+0x22c/0x6b0 kernel/futex.c:2303 > [<ffffffff814c6c3d>] do_futex+0x20d/0x19d0 kernel/futex.c:3067 > [< inline >] SYSC_futex kernel/futex.c:3127 > [<ffffffff814c8533>] SyS_futex+0x133/0x2b0 kernel/futex.c:3095 > [<ffffffff868dafb8>] tracesys_phase2+0x88/0x8d arch/x86/entry/entry_64.S:269 > ---[ end trace 624ab9515f02dd2b ]---
Hit exactly the same use-after-free report without using bpf (just perf_event_open and perf ioctl's).
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