Re: [syzbot] [bpf?] KMSAN: uninit-value in strnchr

[syzbot <syzbot+9b8be5e35747291236c8@syzkaller.appspotmail.com>]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
KMSAN: uninit-value in strnchrnul

=====================================================
BUG: KMSAN: uninit-value in strnchrnul+0xb5/0xf0 lib/string.c:352
 strnchrnul+0xb5/0xf0 lib/string.c:352
 bpf_bprintf_prepare+0x1c2/0x23b0 kernel/bpf/helpers.c:829
 ____bpf_trace_printk kernel/trace/bpf_trace.c:385 [inline]
 bpf_trace_printk+0xec/0x3e0 kernel/trace/bpf_trace.c:375
 ___bpf_prog_run+0x2180/0xdb80 kernel/bpf/core.c:1986
 __bpf_prog_run32+0xb2/0xe0 kernel/bpf/core.c:2225
 bpf_dispatcher_nop_func include/linux/bpf.h:1231 [inline]
 __bpf_prog_run include/linux/filter.h:651 [inline]
 bpf_prog_run include/linux/filter.h:658 [inline]
 bpf_test_run+0x482/0xaf0 net/bpf/test_run.c:423
 bpf_prog_test_run_skb+0x14e5/0x1f20 net/bpf/test_run.c:1056
 bpf_prog_test_run+0x6af/0xac0 kernel/bpf/syscall.c:4107
 __sys_bpf+0x649/0xd60 kernel/bpf/syscall.c:5475
 __do_sys_bpf kernel/bpf/syscall.c:5561 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:5559 [inline]
 __x64_sys_bpf+0xa0/0xe0 kernel/bpf/syscall.c:5559
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcf/0x1e0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x63/0x6b

Local variable stack created at:
 __bpf_prog_run32+0x43/0xe0 kernel/bpf/core.c:2225
 bpf_dispatcher_nop_func include/linux/bpf.h:1231 [inline]
 __bpf_prog_run include/linux/filter.h:651 [inline]
 bpf_prog_run include/linux/filter.h:658 [inline]
 bpf_test_run+0x482/0xaf0 net/bpf/test_run.c:423

CPU: 0 PID: 5507 Comm: syz-executor.0 Not tainted 6.8.0-rc6-syzkaller-00250-g04b8076df253-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
=====================================================


Tested on:

commit:         04b8076d Merge tag 'firewire-fixes-6.8-rc7' of git://g..
git tree:       https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=1470b105180000
kernel config:  https://syzkaller.appspot.com/x/.config?x=80c7a82a572c0de3
dashboard link: https://syzkaller.appspot.com/bug?extid=9b8be5e35747291236c8
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=112caf9d180000