linux-kernel - Re: [syzbot] [bpf?] WARNING in bpf_bprintf

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Message-ID: <68f78ada.050a0220.346f24.0019.GAE@google.com>
Date: Tue, 21 Oct 2025 06:30:02 -0700
From: syzbot <syzbot+b0cff308140f79a9c4cb@...kaller.appspotmail.com>
To: linux-kernel@...r.kernel.org, listout@...tout.xyz, 
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [bpf?] WARNING in bpf_bprintf_prepare (3)

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
WARNING in bpf_bprintf_prepare

------------[ cut here ]------------
WARNING: CPU: 0 PID: 6960 at kernel/bpf/helpers.c:781 bpf_try_get_buffers kernel/bpf/helpers.c:781 [inline]
WARNING: CPU: 0 PID: 6960 at kernel/bpf/helpers.c:781 bpf_bprintf_prepare+0x12cf/0x13a0 kernel/bpf/helpers.c:834
Modules linked in:
CPU: 0 UID: 0 PID: 6960 Comm: syz.1.124 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
RIP: 0010:bpf_try_get_buffers kernel/bpf/helpers.c:781 [inline]
RIP: 0010:bpf_bprintf_prepare+0x12cf/0x13a0 kernel/bpf/helpers.c:834
Code: ff e9 ce fe ff ff e8 10 ec e0 ff e9 be fe ff ff e8 06 ec e0 ff e9 b4 fe ff ff e8 fc eb e0 ff e9 aa fe ff ff e8 f2 eb e0 ff 90 <0f> 0b 90 65 ff 0d 27 ed b2 10 b8 f0 ff ff ff e9 17 ff ff ff e8 d8
RSP: 0018:ffffc9000501f840 EFLAGS: 00010293
RAX: ffffffff81df57fe RBX: ffffc9000501fa10 RCX: ffff88802a138000
RDX: 0000000000000000 RSI: 0000000000000004 RDI: 0000000000000003
RBP: ffffc9000501f970 R08: 0000000000585870 R09: 0000000000000005
R10: dffffc0000000000 R11: fffff52000a03f20 R12: dffffc0000000000
R13: 0000000000000004 R14: 0000000000000003 R15: 1ffff92000a03f42
FS:  00007f8beda4a6c0(0000) GS:ffff888125d0d000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 000000007dee8000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 ____bpf_trace_printk kernel/trace/bpf_trace.c:372 [inline]
 bpf_trace_printk+0xdb/0x190 kernel/trace/bpf_trace.c:362
 bpf_prog_bfbd7bf4bf171090+0x41/0x5a
 bpf_dispatcher_nop_func include/linux/bpf.h:1350 [inline]
 __bpf_prog_run include/linux/filter.h:721 [inline]
 bpf_prog_run include/linux/filter.h:728 [inline]
 bpf_prog_run_pin_on_cpu include/linux/filter.h:745 [inline]
 bpf_flow_dissect+0x225/0x720 net/core/flow_dissector.c:1024
 bpf_prog_test_run_flow_dissector+0x37c/0x5c0 net/bpf/test_run.c:1416
 bpf_prog_test_run+0x2c7/0x340 kernel/bpf/syscall.c:4688
 __sys_bpf+0x562/0x860 kernel/bpf/syscall.c:6167
 __do_sys_bpf kernel/bpf/syscall.c:6259 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:6257 [inline]
 __x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:6257
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f8becb8efc9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f8beda4a038 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
RAX: ffffffffffffffda RBX: 00007f8becde5fa0 RCX: 00007f8becb8efc9
RDX: 0000000000000050 RSI: 0000200000000180 RDI: 000000000000000a
RBP: 00007f8becc11f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f8becde6038 R14: 00007f8becde5fa0 R15: 00007ffeba5c25f8
 </TASK>


Tested on:

commit:         1c64efcb Merge tag 'rust-rustfmt' of git://git.kernel...
git tree:       bpf
console output: https://syzkaller.appspot.com/x/log.txt?x=156d0d2f980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=9ad7b090a18654a7
dashboard link: https://syzkaller.appspot.com/bug?extid=b0cff308140f79a9c4cb
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
patch:          https://syzkaller.appspot.com/x/patch.diff?x=13110d2f980000