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* BUG: assuming atomic context at kernel/seccomp.c:LINE
@ 2019-02-20  9:32 syzbot
  2019-02-20 10:00 ` Daniel Borkmann
  2019-02-20 12:33 ` syzbot
  0 siblings, 2 replies; 4+ messages in thread
From: syzbot @ 2019-02-20  9:32 UTC (permalink / raw)
  To: ast, daniel, kafai, keescook, linux-kernel, luto, netdev,
	songliubraving, syzkaller-bugs, wad, yhs

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
RIP: 0033:0x45ac8a
Code: 25 18 00 00 00 00 74 01 f0 48 0f b1 3d df ba 5f 00 48 39 c2 75 da f3  
c3 0f 1f 84 00 00 00 00 00 48 63 ff b8 e4 00 00 00 0f 05 <48> 3d 00 f0 ff  
ff 77 06 f3 c3 0f 1f 40 00 48 c7 c2 d4 ff ff ff f7
RSP: 002b:00007f92ed7b2c58 EFLAGS: 00000246 ORIG_RAX: 00000000000000e4
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 000000000045ac8a
RDX: 0000000000017230 RSI: 00007f92ed7b2c60 RDI: 0000000000000001
RBP: 000000000073bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00000000004c4cd5 R14: 00000000004d8890 R15: 00000000ffffffff


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#bug-status-tracking for how to communicate with  
syzbot.

^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: BUG: assuming atomic context at kernel/seccomp.c:LINE
  2019-02-20  9:32 BUG: assuming atomic context at kernel/seccomp.c:LINE syzbot
@ 2019-02-20 10:00 ` Daniel Borkmann
  2019-02-20 18:23   ` Kees Cook
  2019-02-20 12:33 ` syzbot
  1 sibling, 1 reply; 4+ messages in thread
From: Daniel Borkmann @ 2019-02-20 10:00 UTC (permalink / raw)
  To: syzbot, ast, kafai, keescook, linux-kernel, luto, netdev,
	songliubraving, syzkaller-bugs, wad, yhs

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

^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: BUG: assuming atomic context at kernel/seccomp.c:LINE
  2019-02-20  9:32 BUG: assuming atomic context at kernel/seccomp.c:LINE syzbot
  2019-02-20 10:00 ` Daniel Borkmann
@ 2019-02-20 12:33 ` syzbot
  1 sibling, 0 replies; 4+ messages in thread
From: syzbot @ 2019-02-20 12:33 UTC (permalink / raw)
  To: ast, daniel, kafai, keescook, linux-kernel, luto, netdev,
	songliubraving, syzkaller-bugs, wad, yhs

syzbot has found a reproducer for 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=101e7fb0c00000
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)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11a52778c00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12a1007cc00000

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: 7853, name: syz-executor140
no locks held by syz-executor140/7853.
CPU: 1 PID: 7853 Comm: syz-executor140 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
RIP: 0033:0x43ec58
Code: 00 00 be 3c 00 00 00 eb 19 66 0f 1f 84 00 00 00 00 00 48 89 d7 89 f0  
0f 05 48 3d 00 f0 ff ff 77 21 f4 48 89 d7 44 89 c0 0f 05 <48> 3d 00 f0 ff  
ff 76 e0 f7 d8 64 41 89 01 eb d8 0f 1f 84 00 00 00
RSP: 002b:00007ffc2d0b2f48 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 000000000043ec58
RDX: 0000000000000000 RSI: 0000000


^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: BUG: assuming atomic context at kernel/seccomp.c:LINE
  2019-02-20 10:00 ` Daniel Borkmann
@ 2019-02-20 18:23   ` Kees Cook
  0 siblings, 0 replies; 4+ messages in thread
From: Kees Cook @ 2019-02-20 18:23 UTC (permalink / raw)
  To: Daniel Borkmann
  Cc: syzbot, Alexei Starovoitov, kafai, LKML, Andy Lutomirski,
	Network Development, Song Liu, syzkaller-bugs, Will Drewry,
	Yonghong Song

On Wed, Feb 20, 2019 at 2:00 AM Daniel Borkmann <daniel@iogearbox.net> wrote:
>
> 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>

Acked-by: Kees Cook <keescook@chromium.org>

-Kees

> ---
>  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



-- 
Kees Cook

^ permalink raw reply	[flat|nested] 4+ messages in thread

end of thread, other threads:[~2019-02-20 18:23 UTC | newest]

Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-02-20  9:32 BUG: assuming atomic context at kernel/seccomp.c:LINE syzbot
2019-02-20 10:00 ` Daniel Borkmann
2019-02-20 18:23   ` Kees Cook
2019-02-20 12:33 ` syzbot

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