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

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit:    04b8076df253 Merge tag 'firewire-fixes-6.8-rc7' of git://g..
git tree:       upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=117de082180000
kernel config:  https://syzkaller.appspot.com/x/.config?x=80c7a82a572c0de3
dashboard link: https://syzkaller.appspot.com/bug?extid=c2dc95f7d0825a145992
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15289dca180000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16bc0bba180000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/a4610b1ff2a7/disk-04b8076d.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/991e9d902d39/vmlinux-04b8076d.xz
kernel image: https://storage.googleapis.com/syzbot-assets/a5b8e8e98121/bzImage-04b8076d.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c2dc95f7d0825a145992@xxxxxxxxxxxxxxxxxxxxxxxxx

=====================================================
BUG: KMSAN: uninit-value in bpf_bprintf_prepare+0x1ec4/0x23b0 kernel/bpf/helpers.c:934
 bpf_bprintf_prepare+0x1ec4/0x23b0 kernel/bpf/helpers.c:934
 ____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: 0 PID: 5018 Comm: syz-executor377 Not tainted 6.8.0-rc6-syzkaller-00250-g04b8076df253 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024
=====================================================


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#syz test: git://repo/address.git branch-or-commit-hash
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