CVE: CVE-2022-50862
Published: 2025-12-30
Description: In the Linux kernel, the following vulnerability has been resolved:

bpf: prevent decl_tag from being referenced in func_proto

Syzkaller was able to hit the following issue:

------------[ cut here ]------------
WARNING: CPU: 0 PID: 3609 at kernel/bpf/btf.c:1946
btf_type_id_size+0x2d5/0x9d0 kernel/bpf/btf.c:1946
Modules linked in:
CPU: 0 PID: 3609 Comm: syz-executor361 Not tainted
6.0.0-syzkaller-02734-g0326074ff465 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 09/22/2022
RIP: 0010:btf_type_id_size+0x2d5/0x9d0 kernel/bpf/btf.c:1946
Code: ef e8 7f 8e e4 ff 41 83 ff 0b 77 28 f6 44 24 10 18 75 3f e8 6d 91
e4 ff 44 89 fe bf 0e 00 00 00 e8 20 8e e4 ff e8 5b 91 e4 ff <0f> 0b 45
31 f6 e9 98 02 00 00 41 83 ff 12 74 18 e8 46 91 e4 ff 44
RSP: 0018:ffffc90003cefb40 EFLAGS: 00010293
RAX: [PII_REDACTED] RBX: [PII_REDACTED] RCX: [PII_REDACTED]
RDX: ffff8880259c0000 RSI: ffffffff81968415 RDI: [PII_REDACTED]
RBP: ffff88801270ca00 R08: [PII_REDACTED] R09:[PII_REDACTED]00000e
R10: [PII_REDACTED] R11: [PII_REDACTED] R12: [PII_REDACTED]
R13: [PII_REDACTED] R14: ffff888026ee6424 R15: [PII_REDACTED]
FS: [PII_REDACTED]41b300(0000) GS:ffff8880b9a00000(0000)
knlGS:[PII_REDACTED]
CS:  0010 DS: 0000 ES: 0000 CR0: [PII_REDACTED]
CR2:[PII_REDACTED]f2e258 CR3:[PII_REDACTED]10e000 CR4:[PII_REDACTED]3506f0
DR0: [PII_REDACTED] DR1: [PII_REDACTED] DR2: [PII_REDACTED]
DR3: [PII_REDACTED] DR6: 00000000fffe0ff0 DR7: [PII_REDACTED]
Call Trace:
 <TASK>
 btf_func_proto_check kernel/bpf/btf.c:4447 [inline]
 btf_check_all_types kernel/bpf/btf.c:4723 [inline]
 btf_parse_type_sec kernel/bpf/btf.c:4752 [inline]
 btf_parse kernel/bpf/btf.c:5026 [inline]
 btf_new_fd+0x1926/0x1e70 kernel/bpf/btf.c:6892
 bpf_btf_load kernel/bpf/syscall.c:4324 [inline]
 __sys_bpf+0xb7d/0x4cf0 kernel/bpf/syscall.c:5010
 __do_sys_bpf kernel/bpf/syscall.c:5069 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:5067 [inline]
 __x64_sys_bpf+0x75/0xb0 kernel/bpf/syscall.c:5067
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f0fbae41c69
Code: 28 c3 e8 2a 14 00 00 66 2e 0f 1f 84 00 00 00 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 c0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffc8aeb6228 EFLAGS: 00000246 ORIG_RAX: [PII_REDACTED]
RAX: ffffffffffffffda RBX: [PII_REDACTED] RCX: 00007f0fbae41c69
RDX: [PII_REDACTED] RSI: [PII_REDACTED] RDI: [PII_REDACTED]
RBP: 00007f0fbae05e10 R08: [PII_REDACTED] R09: [PII_REDACTED]
R10: 00000000ffffffff R11: [PII_REDACTED] R12: 00007f0fbae05ea0
R13: [PII_REDACTED] R14: [PII_REDACTED] R15: [PII_REDACTED]
 </TASK>

Looks like it tries to create a func_proto which return type is
decl_tag. For the details, see Martin's spot on analysis in [0].

0: https://lore.kernel.org/bpf/CAKH8qBuQDLva_hHxxBuZzyAcYNO4ejhovz6TQeVSk8HY-2SO6g@mail.gmail.com/T/#mea6524b3fcd[PII_REDACTED]226e81b1e6155efc62c
References: https://git.kernel.org/stable/c/e9dbb4c539d058852b76937dcd7347d3f38054f2; https://git.kernel.org/stable/c/ea68376c8bed5cd156900852aada20c3a0874d17