From: "Toke Høiland-Jørgensen" <toke@kernel.org>
To: John Fastabend <john.fastabend@gmail.com>,
syzbot <syzbot+8cd36f6b65f3cafd400a@syzkaller.appspotmail.com>,
andrii@kernel.org, ast@kernel.org, bpf@vger.kernel.org,
daniel@iogearbox.net, davem@davemloft.net, haoluo@google.com,
hawk@kernel.org, john.fastabend@gmail.com, jolsa@kernel.org,
kpsingh@kernel.org, kuba@kernel.org,
linux-kernel@vger.kernel.org, martin.lau@linux.dev,
netdev@vger.kernel.org, sdf@google.com, song@kernel.org,
syzkaller-bugs@googlegroups.com, yonghong.song@linux.dev
Subject: Re: [syzbot] [bpf?] [net?] BUG: unable to handle kernel NULL pointer dereference in dev_map_hash_update_elem
Date: Tue, 27 Feb 2024 14:50:10 +0100 [thread overview]
Message-ID: <87msrmdnjh.fsf@toke.dk> (raw)
In-Reply-To: <65dd075bc6cbd_20e0a20892@john.notmuch>
John Fastabend <john.fastabend@gmail.com> writes:
> syzbot wrote:
>> syzbot has found a reproducer for the following issue on:
>>
>> HEAD commit: 70ff1fe626a1 Merge tag 'docs-6.8-fixes3' of git://git.lwn...
>> git tree: upstream
>> console output: https://syzkaller.appspot.com/x/log.txt?x=1762045c180000
>> kernel config: https://syzkaller.appspot.com/x/.config?x=4cf52b43f46d820d
>> dashboard link: https://syzkaller.appspot.com/bug?extid=8cd36f6b65f3cafd400a
>> compiler: arm-linux-gnueabi-gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
>> userspace arch: arm
>> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=110cf122180000
>> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=142f6d8c180000
>>
>> Downloadable assets:
>> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/8ead8862021c/non_bootable_disk-70ff1fe6.raw.xz
>> vmlinux: https://storage.googleapis.com/syzbot-assets/bc398db9fd8c/vmlinux-70ff1fe6.xz
>> kernel image: https://storage.googleapis.com/syzbot-assets/6d3f8b72a671/zImage-70ff1fe6.xz
>>
>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
>> Reported-by: syzbot+8cd36f6b65f3cafd400a@syzkaller.appspotmail.com
>>
>
> I'll take a look this week if no one beats me to it. Looks like there is
> a reproducer so should be able to sort it out.
Took a look at the reproducer. Looks like it's creating the map with
max_entries=0x80000202, which means the rounding up of the number of
hash buckets overflows, and somehow the overflow check (for 0) is not
working on a 32-bit machine? I guess because the roundup_power_of_two()
ends up doing a (1UL << 32), which is undefined behaviour when an
unsigned long is four bytes.
I'll send a patch to check the value before the rounding up instead of
after.
-Toke
next prev parent reply other threads:[~2024-02-27 13:50 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-18 22:22 [syzbot] [net?] [bpf?] BUG: unable to handle kernel NULL pointer dereference in dev_map_hash_update_elem syzbot
2024-02-26 3:49 ` [syzbot] [bpf?] [net?] " syzbot
2024-02-26 21:49 ` John Fastabend
2024-02-27 13:50 ` Toke Høiland-Jørgensen [this message]
2024-02-27 13:52 ` [syzbot] " syzbot
[not found] <87jzmqdnfv.fsf@toke.dk>
2024-02-27 14:16 ` syzbot
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