linux-kernel - Re: [syzbot] KMSAN: uninit-value in fib_get

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Date:   Fri, 10 Dec 2021 09:52:40 -0700
From:   David Ahern <dsahern@...il.com>
To:     syzbot <syzbot+d4b9a2851cc3ce998741@...kaller.appspotmail.com>,
        davem@...emloft.net, dsahern@...nel.org, glider@...gle.com,
        kuba@...nel.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, syzkaller-bugs@...glegroups.com,
        yoshfuji@...ux-ipv6.org
Subject: Re: [syzbot] KMSAN: uninit-value in fib_get_nhs

On 12/9/21 11:57 AM, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    8b936c96768e kmsan: core: remove the accidentally committe..
> git tree:       https://github.com/google/kmsan.git master
> console output: https://syzkaller.appspot.com/x/log.txt?x=1724ebc5b00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=e00a8959fdd3f3e8
> dashboard link: https://syzkaller.appspot.com/bug?extid=d4b9a2851cc3ce998741
> compiler:       clang version 14.0.0 (git@...hub.com:llvm/llvm-project.git 0996585c8e3b3d409494eb5f1cad714b9e1f7fb5), GNU ld (GNU Binutils for Debian) 2.35.2
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1225f875b00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=139513c5b00000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+d4b9a2851cc3ce998741@...kaller.appspotmail.com
> 
> =====================================================
> BUG: KMSAN: uninit-value in fib_get_nhs+0xac4/0x1f80 net/ipv4/fib_semantics.c:708


Most likely lack of length validation on nla like we have in
fib_gw_from_via for the other attribute (nlav). Will send a patch.