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

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Message-ID: <CAADnVQKRsUcPkWBBA0442jakf-6dr9n9dii9pjSsSyqRS6NcgA@mail.gmail.com>
Date: Fri, 13 Jun 2025 09:10:38 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Eduard Zingerman <eddyz87@...il.com>
Cc: syzbot <syzbot+a36aac327960ff474804@...kaller.appspotmail.com>, 
	Andrii Nakryiko <andrii@...nel.org>, Alexei Starovoitov <ast@...nel.org>, bpf <bpf@...r.kernel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, Hao Luo <haoluo@...gle.com>, 
	John Fastabend <john.fastabend@...il.com>, Jiri Olsa <jolsa@...nel.org>, 
	KP Singh <kpsingh@...nel.org>, LKML <linux-kernel@...r.kernel.org>, 
	Martin KaFai Lau <martin.lau@...ux.dev>, Network Development <netdev@...r.kernel.org>, 
	Stanislav Fomichev <sdf@...ichev.me>, Song Liu <song@...nel.org>, 
	syzkaller-bugs <syzkaller-bugs@...glegroups.com>, Yonghong Song <yonghong.song@...ux.dev>
Subject: Re: [syzbot] [bpf?] WARNING in do_check

On Fri, Jun 13, 2025 at 12:56 AM Eduard Zingerman <eddyz87@...il.com> wrote:
>
> On Fri, 2025-06-13 at 00:12 -0700, syzbot wrote:
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit:    1c66f4a3612c bpf: Fix state use-after-free on push_stack()..
> > git tree:       bpf-next
> > console+strace: https://syzkaller.appspot.com/x/log.txt?x=1346ed70580000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=73696606574e3967
> > dashboard link: https://syzkaller.appspot.com/bug?extid=a36aac327960ff474804
> > compiler:       Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1392610c580000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11a9ee0c580000
> >
> > Downloadable assets:
> > disk image: https://storage.googleapis.com/syzbot-assets/2ddb1df1c757/disk-1c66f4a3.raw.xz
> > vmlinux: https://storage.googleapis.com/syzbot-assets/6a318fc92af0/vmlinux-1c66f4a3.xz
> > kernel image: https://storage.googleapis.com/syzbot-assets/76c58dddcb6c/bzImage-1c66f4a3.xz
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+a36aac327960ff474804@...kaller.appspotmail.com
> >
> > ------------[ cut here ]------------
>
> Fwiw, here is a repro converted to selftest.
> I'll take detailed look on Friday:
>
> SEC("socket")
> __naked void syzbot_repro(void)
> {
>         asm volatile (
>         "r8 = 0xff80;"
>         "r1 = 0xff110001085a0800 ll;"
>         "r2 = 20;"
>         "r3 = 0;"
>         "call %[bpf_ktime_get_ns];"
> "1:"
>         "w9 = w10;"
>         "if r9 >= 0xff4ad400 goto 2f;"
>         "may_goto +13;"
>         "r2 = 0;"
>         "*(u8 *)(r10 -16) = r9;"
> "2:"
>         "if r9 s< 0x1004 goto 3f;"
>         "lock *(u32 *)(r10 -16) += r10;"
>         "r6 = r8;"
>         "r8 += -8;"
>         "r4 = r10;"
> "3:"
>         "r6 += -16;"
>         "r2 = 8;"
>         "r2 = 0xff110001085a05d8 ll;"
>         "r5 = 8;"
>         "if w8 & 0x76 goto 1b;"

I suspect this might be the fix:

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index c378074516cf..e76eb0322912 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -23950,6 +23950,7 @@ static bool can_jump(struct bpf_insn *insn)
        case BPF_JSLT:
        case BPF_JSLE:
        case BPF_JCOND:
+       case BPF_JSET:
                return true;
        }