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verifier bug: backtracking misuse
WARNING: kernel/bpf/backtrack.c:819 at bpf_mark_chain_precision+0x5c90/0x7c20 kernel/bpf/backtrack.c:819, CPU#1: syz-executor123/5627
Modules linked in:
CPU: 1 UID: 0 PID: 5627 Comm: syz-executor123 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:bpf_mark_chain_precision+0x5c90/0x7c20 kernel/bpf/backtrack.c:819
Code: ff 89 d9 80 e1 07 80 c1 03 38 c1 0f 8c 16 ff ff ff 48 89 df e8 c1 7b 44 00 e9 09 ff ff ff e8 77 b2 d4 ff 48 8d 3d a0 0c 8b 0e <67> 48 0f b9 3a 48 8b 3c 24 48 81 c7 88 08 00 00 48 c7 c6 60 df 16
RSP: 0018:ffffc9000386f220 EFLAGS: 00010293
RAX: ffffffff81f308a9 RBX: 0000000000000001 RCX: ffff888029cd3e80
RDX: 0000000000000000 RSI: 0000000000000003 RDI: ffffffff907e1550
RBP: 0000000000000003 R08: ffff888029cd3e80 R09: 0000000000000003
R10: 0000000000000007 R11: 0000000000000000 R12: ffff88807f2a5850
R13: dffffc0000000000 R14: 0000000000000001 R15: 0000000000000000
FS:  0000555568797400(0000) GS:ffff888124dd9000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000006a9ee0 CR3: 0000000079e78000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 mark_chain_precision kernel/bpf/verifier.c:3371 [inline]
 check_helper_call kernel/bpf/verifier.c:10892 [inline]
 do_check_insn+0x12c6d/0x17d70 kernel/bpf/verifier.c:18144
 do_check kernel/bpf/verifier.c:18330 [inline]
 do_check_common+0x3c19/0x5d30 kernel/bpf/verifier.c:19411
 do_check_main kernel/bpf/verifier.c:19507 [inline]
 bpf_check+0x2639/0x2e10 kernel/bpf/verifier.c:21162
 bpf_prog_load+0x14d6/0x1c20 kernel/bpf/syscall.c:3133
 __sys_bpf+0xd0d/0xd90 kernel/bpf/syscall.c:6367
 __do_sys_bpf kernel/bpf/syscall.c:6486 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:6483 [inline]
 __x64_sys_bpf+0xba/0xd0 kernel/bpf/syscall.c:6483
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f0d20535ef9
Code: c0 79 93 eb d5 48 8d 7c 1d 00 eb 99 0f 1f 44 00 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 d8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fff9b080398 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
RAX: ffffffffffffffda RBX: 0000200000000000 RCX: 00007f0d20535ef9
RDX: 0000000000000080 RSI: 0000200000000300 RDI: 0000000000000005
RBP: 0000000000000001 R08: 00007fff9b0804c8 R09: 00007fff9b0804c8
R10: 00007fff9b0804c8 R11: 0000000000000246 R12: 00007fff9b0804b8
R13: 0000000000000002 R14: 00007f0d205c6ca0 R15: 0000000000000002
 </TASK>
----------------
Code disassembly (best guess):
   0:	ff 89 d9 80 e1 07    	decl   0x7e180d9(%rcx)
   6:	80 c1 03             	add    $0x3,%cl
   9:	38 c1                	cmp    %al,%cl
   b:	0f 8c 16 ff ff ff    	jl     0xffffff27
  11:	48 89 df             	mov    %rbx,%rdi
  14:	e8 c1 7b 44 00       	call   0x447bda
  19:	e9 09 ff ff ff       	jmp    0xffffff27
  1e:	e8 77 b2 d4 ff       	call   0xffd4b29a
  23:	48 8d 3d a0 0c 8b 0e 	lea    0xe8b0ca0(%rip),%rdi        # 0xe8b0cca
* 2a:	67 48 0f b9 3a       	ud1    (%edx),%rdi <-- trapping instruction
  2f:	48 8b 3c 24          	mov    (%rsp),%rdi
  33:	48 81 c7 88 08 00 00 	add    $0x888,%rdi
  3a:	48                   	rex.W
  3b:	c7                   	.byte 0xc7
  3c:	c6                   	(bad)
  3d:	60                   	(bad)
  3e:	df 16                	fists  (%rsi)