[syzbot] [bpf?] KMSAN: uninit-value in bstr_printf

syzbot
2024-02-21T20:55:23Z

Hello,

syzbot found the following issue on:

HEAD commit: c1ca10ceffbb Merge tag 'scsi-fixes' of git://git.kernel.or..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10e7f5f0180000
kernel config: https://syzkaller.appspot.com/x/.config?x=e3dd779fba027968
dashboard link: https://syzkaller.appspot.com/bug?extid=f0d29b273acdcd3a2562
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/83d019f0ac47/disk-c1ca10ce.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/49e05dd7a23d/vmlinux-c1ca10ce.xz
kernel image: https://storage.googleapis.com/syzbot-assets/68ec9fa2d33d/bzImage-c1ca10ce.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f0d29b273acdcd3a2562@syzkaller.appspotmail.com

=====================================================
BUG: KMSAN: uninit-value in bstr_printf+0x19df/0x1b50 lib/vsprintf.c:3334
bstr_printf+0x19df/0x1b50 lib/vsprintf.c:3334
____bpf_snprintf kernel/bpf/helpers.c:1064 [inline]
bpf_snprintf+0x1c8/0x360 kernel/bpf/helpers.c:1044
___bpf_prog_run+0x2180/0xdb80 kernel/bpf/core.c:1986
__bpf_prog_run288+0xb5/0xe0 kernel/bpf/core.c:2226
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_prog_run_pin_on_cpu include/linux/filter.h:675 [inline]
bpf_flow_dissect+0x127/0x470 net/core/flow_dissector.c:991
bpf_prog_test_run_flow_dissector+0x6f4/0xa20 net/bpf/test_run.c:1359
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

Uninit was stored to memory at:
bpf_bprintf_prepare+0x138d/0x23b0 kernel/bpf/helpers.c:1027
____bpf_snprintf kernel/bpf/helpers.c:1060 [inline]
bpf_snprintf+0x141/0x360 kernel/bpf/helpers.c:1044
___bpf_prog_run+0x2180/0xdb80 kernel/bpf/core.c:1986
__bpf_prog_run288+0xb5/0xe0 kernel/bpf/core.c:2226
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_prog_run_pin_on_cpu include/linux/filter.h:675 [inline]
bpf_flow_dissect+0x127/0x470 net/core/flow_dissector.c:991
bpf_prog_test_run_flow_dissector+0x6f4/0xa20 net/bpf/test_run.c:1359
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_run288+0x45/0xe0 kernel/bpf/core.c:2226
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_prog_run_pin_on_cpu include/linux/filter.h:675 [inline]
bpf_flow_dissect+0x127/0x470 net/core/flow_dissector.c:991

CPU: 1 PID: 8904 Comm: syz-executor.2 Not tainted 6.8.0-rc4-syzkaller-00331-gc1ca10ceffbb #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024
=====================================================

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