Messages in this thread Patch in this message | | | Subject | Re: BUG: assuming atomic context at kernel/seccomp.c:LINE | From | Daniel Borkmann <> | Date | Wed, 20 Feb 2019 11:00:19 +0100 |
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On 02/20/2019 10:32 AM, syzbot wrote: > Hello, > > syzbot found the following crash on: > > HEAD commit: abf446c90405 Add linux-next specific files for 20190220 > git tree: linux-next > console output: https://syzkaller.appspot.com/x/log.txt?x=17f250d8c00000 > kernel config: https://syzkaller.appspot.com/x/.config?x=463cb576ac40e350 > dashboard link: https://syzkaller.appspot.com/bug?extid=8bf19ee2aa580de7a2a7 > compiler: gcc (GCC) 9.0.0 20181231 (experimental) > > Unfortunately, I don't have any reproducer for this crash yet. > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > Reported-by: syzbot+8bf19ee2aa580de7a2a7@syzkaller.appspotmail.com > > BUG: assuming atomic context at kernel/seccomp.c:271 > in_atomic(): 0, irqs_disabled(): 0, pid: 12803, name: syz-executor.5 > no locks held by syz-executor.5/12803. > CPU: 1 PID: 12803 Comm: syz-executor.5 Not tainted 5.0.0-rc7-next-20190220 #39 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > Call Trace: > __dump_stack lib/dump_stack.c:77 [inline] > dump_stack+0x172/0x1f0 lib/dump_stack.c:113 > __cant_sleep kernel/sched/core.c:6218 [inline] > __cant_sleep.cold+0xa3/0xbb kernel/sched/core.c:6195 > seccomp_run_filters kernel/seccomp.c:271 [inline] > __seccomp_filter+0x12b/0x12b0 kernel/seccomp.c:801 > __secure_computing+0x101/0x360 kernel/seccomp.c:932 > syscall_trace_enter+0x5bf/0xe10 arch/x86/entry/common.c:120 > do_syscall_64+0x479/0x610 arch/x86/entry/common.c:280 > entry_SYSCALL_64_after_hwframe+0x49/0xbe
False positive; bpf-next only. Pushing this out in a bit:
From d56547070162a105ff666f3324e558fa6492aedd Mon Sep 17 00:00:00 2001 From: Daniel Borkmann <daniel@iogearbox.net> Date: Wed, 20 Feb 2019 10:51:17 +0100 Subject: [PATCH bpf-next] bpf, seccomp: fix false positive preemption splat for cbpf->ebpf progs
In 568f196756ad ("bpf: check that BPF programs run with preemption disabled") a check was added for BPF_PROG_RUN() that for every invocation preemption is disabled to not break eBPF assumptions (e.g. per-cpu map). Of course this does not count for seccomp because only cBPF -> eBPF is loaded here and it does not make use of any functionality that would require this assertion. Fix this false positive by adding and using __BPF_PROG_RUN() variant that does not have the cant_sleep(); check.
Fixes: 568f196756ad ("bpf: check that BPF programs run with preemption disabled") Reported-by: syzbot+8bf19ee2aa580de7a2a7@syzkaller.appspotmail.com Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> --- include/linux/filter.h | 9 ++++++++- kernel/seccomp.c | 2 +- 2 files changed, 9 insertions(+), 2 deletions(-)
diff --git a/include/linux/filter.h b/include/linux/filter.h index f32b3ec..2f3e29a 100644 --- a/include/linux/filter.h +++ b/include/linux/filter.h @@ -533,7 +533,14 @@ struct sk_filter { struct bpf_prog *prog; };
-#define BPF_PROG_RUN(filter, ctx) ({ cant_sleep(); (*(filter)->bpf_func)(ctx, (filter)->insnsi); }) +#define bpf_prog_run__non_preempt(prog, ctx) \ + ({ cant_sleep(); __BPF_PROG_RUN(prog, ctx); }) +/* Native eBPF or cBPF -> eBPF transitions. Preemption must be disabled. */ +#define BPF_PROG_RUN(prog, ctx) \ + bpf_prog_run__non_preempt(prog, ctx) +/* cBPF -> eBPF only, but not for native eBPF. */ +#define __BPF_PROG_RUN(prog, ctx) \ + (*(prog)->bpf_func)(ctx, (prog)->insnsi)
#define BPF_SKB_CB_LEN QDISC_CB_PRIV_LEN
diff --git a/kernel/seccomp.c b/kernel/seccomp.c index e815781..826d4e4 100644 --- a/kernel/seccomp.c +++ b/kernel/seccomp.c @@ -268,7 +268,7 @@ static u32 seccomp_run_filters(const struct seccomp_data *sd, * value always takes priority (ignoring the DATA). */ for (; f; f = f->prev) { - u32 cur_ret = BPF_PROG_RUN(f->prog, sd); + u32 cur_ret = __BPF_PROG_RUN(f->prog, sd);
if (ACTION_ONLY(cur_ret) < ACTION_ONLY(ret)) { ret = cur_ret; -- 2.9.5
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