WARNING in format_decode (2)

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 2ad0d5269970 Merge git://git.kernel.org/pub/scm/linux/kern..
git tree: net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=15b8efba400000
kernel config: https://syzkaller.appspot.com/x/.config?x=79e695838ce7a210
dashboard link: https://syzkaller.appspot.com/bug?extid=1ec5c5ec949c4adaa0c4
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1626f761400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+1ec5c5...@syzkaller.appspotmail.com

** **
** NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE **
**********************************************************
------------[ cut here ]------------
Please remove unsupported % in format string
WARNING: CPU: 0 PID: 6453 at lib/vsprintf.c:2149 format_decode+0x8fc/0xaf0
lib/vsprintf.c:2149
Kernel panic - not syncing: panic_on_warn set ...

CPU: 0 PID: 6453 Comm: syz-executor7 Not tainted 4.18.0+ #190
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+0x1c9/0x2b4 lib/dump_stack.c:113
panic+0x238/0x4e7 kernel/panic.c:184
__warn.cold.8+0x163/0x1ba kernel/panic.c:536
report_bug+0x252/0x2d0 lib/bug.c:186
fixup_bug arch/x86/kernel/traps.c:178 [inline]
do_error_trap+0x1fc/0x4d0 arch/x86/kernel/traps.c:296
do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:316
invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:993
RIP: 0010:format_decode+0x8fc/0xaf0 lib/vsprintf.c:2149
Code: e8 59 59 c9 fa 41 c6 04 24 12 e9 94 fd ff ff e8 4a 59 c9 fa 0f be f3
48 c7 c7 60 bc 89 87 c6 05 28 aa d2 01 01 e8 e4 e9 93 fa <0f> 0b 4d 8b 7d
c0 e9 56 fe ff ff 48 8b bd 68 ff ff ff e8 cd 4f 08
RSP: 0018:ffff8801b6b27688 EFLAGS: 00010282
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff816422b1 RDI: ffff8801b6b27378
RBP: ffff8801b6b27730 R08: ffff8801b69a0040 R09: 0000000000000006
R10: 0000000000000000 R11: 0000000000000000 R12: ffff8801b6b277a8
R13: ffff8801b6b27708 R14: 0000000000000000 R15: ffff8801b6b27b04
vsnprintf+0x185/0x1b60 lib/vsprintf.c:2245
vscnprintf+0x2d/0x80 lib/vsprintf.c:2396
__trace_array_vprintk.part.60+0xc7/0x330 kernel/trace/trace.c:2990
__trace_array_vprintk kernel/trace/trace.c:3021 [inline]
trace_array_vprintk kernel/trace/trace.c:3021 [inline]
trace_vprintk+0x5f/0x90 kernel/trace/trace.c:3059
__trace_printk+0xce/0x120 kernel/trace/trace_printk.c:237
____bpf_trace_printk kernel/trace/bpf_trace.c:274 [inline]
bpf_trace_printk+0xb16/0xc30 kernel/trace/bpf_trace.c:166
bpf_prog_e51deac1441bc083+0x94a/0x1000
Dumping ftrace buffer:
(ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..


---
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[Steven Rostedt]

On Mon, 27 Aug 2018 10:10:04 -0700
syzbot <syzbot+1ec5c5...@syzkaller.appspotmail.com> wrote:

> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit: 2ad0d5269970 Merge git://git.kernel.org/pub/scm/linux/kern..
> git tree: net-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=15b8efba400000
> kernel config: https://syzkaller.appspot.com/x/.config?x=79e695838ce7a210
> dashboard link: https://syzkaller.appspot.com/bug?extid=1ec5c5ec949c4adaa0c4
> compiler: gcc (GCC) 8.0.1 20180413 (experimental)
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1626f761400000
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+1ec5c5...@syzkaller.appspotmail.com
>
> ** **
> ** NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE **
> **********************************************************
> ------------[ cut here ]------------

> Please remove unsupported %WARNING: CPU: 0 PID: 6453 at lib/vsprintf.c:2149 format_decode+0x8fc/0xaf0

Looks like a bug in the bpf trace printk code.

-- Steve

[Alexei Starovoitov]

yes. looks like %p% slipped past bpf_trace_printk() runtime checks.

[syzbot]

syzbot has found a reproducer for the following crash on:

HEAD commit: da85d8bfd151 kselftests/bpf: use ping6 as the default ipv6..
git tree: bpf
console output: https://syzkaller.appspot.com/x/log.txt?x=116bf533400000
kernel config: https://syzkaller.appspot.com/x/.config?x=8f559fee2fc3375a

dashboard link: https://syzkaller.appspot.com/bug?extid=1ec5c5ec949c4adaa0c4
compiler: gcc (GCC) 8.0.1 20180413 (experimental)

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16d03247400000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=104f5533400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+1ec5c5...@syzkaller.appspotmail.com

** **
** NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE **
**********************************************************
------------[ cut here ]------------
Please remove unsupported % in format string

WARNING: CPU: 0 PID: 5654 at lib/vsprintf.c:2152 format_decode+0x8fc/0xaf0
lib/vsprintf.c:2152

Kernel panic - not syncing: panic_on_warn set ...

CPU: 0 PID: 5654 Comm: syz-executor818 Not tainted 4.20.0-rc1+ #80

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+0x244/0x39d lib/dump_stack.c:113
panic+0x2ad/0x55c kernel/panic.c:188
__warn.cold.8+0x20/0x45 kernel/panic.c:540
report_bug+0x254/0x2d0 lib/bug.c:186
fixup_bug arch/x86/kernel/traps.c:178 [inline]
do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:271
do_invalid_op+0x36/0x40 arch/x86/kernel/traps.c:290
invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:969
RIP: 0010:format_decode+0x8fc/0xaf0 lib/vsprintf.c:2152
Code: e8 c9 37 b5 f9 41 c6 45 00 12 e9 9b fd ff ff e8 ba 37 b5 f9 0f be f3
48 c7 c7 c0 f1 d5 88 c6 05 d2 08 47 02 01 e8 74 99 7e f9 <0f> 0b 4d 8b 66
c0 e9 59 fe ff ff 48 8b bd 70 ff ff ff e8 6d 84 f8
RSP: 0018:ffff8801ba76f670 EFLAGS: 00010286

RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000

RDX: 0000000000000000 RSI: ffffffff8165e9b5 RDI: 0000000000000005
RBP: ffff8801ba76f718 R08: ffff8801b6cfc0c0 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff8801ba76faec
R13: ffff8801ba76f790 R14: ffff8801ba76f6f0 R15: 0000000000000000
vsnprintf+0x185/0x1b60 lib/vsprintf.c:2248
vscnprintf+0x2d/0x80 lib/vsprintf.c:2399
__trace_array_vprintk.part.59+0x5b/0x2f0 kernel/trace/trace.c:2992
__trace_array_vprintk kernel/trace/trace.c:3023 [inline]
trace_array_vprintk kernel/trace/trace.c:3023 [inline]
trace_vprintk+0x71/0x90 kernel/trace/trace.c:3061
__trace_printk+0xce/0x120 kernel/trace/trace_printk.c:238
____bpf_trace_printk kernel/trace/bpf_trace.c:271 [inline]
bpf_trace_printk+0xb30/0xc50 kernel/trace/bpf_trace.c:163
bpf_prog_12183cdb1cd51dab+0x3e7/0x1000