Re: [syzbot] [bpf?] WARNING in do_misc_fixups

[Jiri Olsa <olsajiri@gmail.com>]

On Sun, Aug 03, 2025 at 10:08:32PM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    a6923c06a3b2 Merge tag 'bpf-fixes' of git://git.kernel.org..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=1561dcf0580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=f89bb9497754f485
> dashboard link: https://syzkaller.appspot.com/bug?extid=a9ed3d9132939852d0df
> compiler:       aarch64-linux-gnu-gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> userspace arch: arm64
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=165d0aa2580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=117bd834580000
> 
> Downloadable assets:
> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/fa3fbcfdac58/non_bootable_disk-a6923c06.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/9862ca8219e0/vmlinux-a6923c06.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/042ebe320cfd/Image-a6923c06.gz.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+a9ed3d9132939852d0df@syzkaller.appspotmail.com
> 
> ------------[ cut here ]------------
> verifier bug: not inlined functions bpf_probe_read_kernel_str#115 is missing func(1)
> WARNING: CPU: 1 PID: 3594 at kernel/bpf/verifier.c:22838 do_misc_fixups+0x1784/0x1ab4 kernel/bpf/verifier.c:22838
> Modules linked in:
> CPU: 1 UID: 0 PID: 3594 Comm: syz.2.17 Not tainted 6.16.0-syzkaller-11105-ga6923c06a3b2 #0 PREEMPT 
> Hardware name: linux,dummy-virt (DT)
> pstate: 61402009 (nZCv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--)
> pc : do_misc_fixups+0x1784/0x1ab4 kernel/bpf/verifier.c:22838
> lr : do_misc_fixups+0x1784/0x1ab4 kernel/bpf/verifier.c:22838
> sp : ffff80008936b9a0
> x29: ffff80008936b9a0 x28: f5ff8000832f5000 x27: 000000000000000a
> x26: f8f0000007ba8000 x25: 0000000000000000 x24: f8f0000007bae200
> x23: 000000000000f0ff x22: 000000000000000a x21: f8f0000007bae128
> x20: f8f0000007ba8aa8 x19: ffff80008243e828 x18: 0000000000000000
> x17: 0000000000000000 x16: 0000000000000000 x15: ffff800081b73b80
> x14: 0000000000000342 x13: 0000000000000000 x12: 0000000000000002
> x11: 00000000000000c0 x10: 646e0773d90f24cc x9 : 73727a981a23afd7
> x8 : fcf0000007bb36f8 x7 : 0000000000000190 x6 : 0000003978391654
> x5 : 0000000000000001 x4 : fbffff3fffffffff x3 : 000000000000ffff
> x2 : 0000000000000000 x1 : 0000000000000000 x0 : fcf0000007bb2500
> Call trace:
>  do_misc_fixups+0x1784/0x1ab4 kernel/bpf/verifier.c:22838 (P)
>  bpf_check+0x1308/0x2a8c kernel/bpf/verifier.c:24739
>  bpf_prog_load+0x634/0xb74 kernel/bpf/syscall.c:2979
>  __sys_bpf+0x2e0/0x1a3c kernel/bpf/syscall.c:6029
>  __do_sys_bpf kernel/bpf/syscall.c:6139 [inline]
>  __se_sys_bpf kernel/bpf/syscall.c:6137 [inline]
>  __arm64_sys_bpf+0x24/0x34 kernel/bpf/syscall.c:6137
>  __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
>  invoke_syscall+0x48/0x110 arch/arm64/kernel/syscall.c:49
>  el0_svc_common.constprop.0+0x40/0xe0 arch/arm64/kernel/syscall.c:132
>  do_el0_svc+0x1c/0x28 arch/arm64/kernel/syscall.c:151
>  el0_svc+0x34/0x10c arch/arm64/kernel/entry-common.c:879
>  el0t_64_sync_handler+0xa0/0xe4 arch/arm64/kernel/entry-common.c:898
>  el0t_64_sync+0x1a4/0x1a8 arch/arm64/kernel/entry.S:596
> ---[ end trace 0000000000000000 ]---
> 
> 
> ---
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trying suggested fix by Alexei

jirka


#syz test

---
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 0806295945e4..6aa303f76849 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -11344,6 +11344,13 @@ static bool can_elide_value_nullness(enum bpf_map_type type)
 	}
 }
 
+static bool is_valid_proto(const struct bpf_func_proto *fn, int func_id)
+{
+	if (func_id == BPF_FUNC_tail_call)
+		return true;
+	return fn && fn->func;
+}
+
 static int get_helper_proto(struct bpf_verifier_env *env, int func_id,
 			    const struct bpf_func_proto **ptr)
 {
@@ -11354,7 +11361,7 @@ static int get_helper_proto(struct bpf_verifier_env *env, int func_id,
 		return -EINVAL;
 
 	*ptr = env->ops->get_func_proto(func_id, env->prog);
-	return *ptr ? 0 : -EINVAL;
+	return is_valid_proto(*ptr, func_id) ? 0 : -EINVAL;
 }
 
 static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn,