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+1ec5c5ec949c4adaa0c4@xxxxxxxxxxxxxxxxxxxxxxxxx

**                                                      **
**   NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE   **
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------------[ 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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