linux-kernel - Re: [PATCH v2] net: sctp: fix KMSAN uninit-value in sctp_inq

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Message-ID: <CADvbK_dgLr5dUVqc=hxjj3n8wn8azkAp=K2Jr-pcuzUBk+et1Q@mail.gmail.com>
Date: Fri, 24 Oct 2025 12:01:48 -0400
From: Xin Long <lucien.xin@...il.com>
To: Ranganath V N <vnranganath.20@...il.com>
Cc: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Simon Horman <horms@...nel.org>, linux-sctp@...r.kernel.org, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com, 
	syzbot+d101e12bccd4095460e7@...kaller.appspotmail.com
Subject: Re: [PATCH v2] net: sctp: fix KMSAN uninit-value in sctp_inq_pop

On Fri, Oct 24, 2025 at 7:44 AM Ranganath V N <vnranganath.20@...il.com> wrote:
>
> Fix an issue detected by syzbot:
>
> KMSAN reported an uninitialized-value access in sctp_inq_pop
> BUG: KMSAN: uninit-value in sctp_inq_pop
>
> The issue is actually caused by skb trimming via sk_filter() in sctp_rcv().
> In the reproducer, skb->len becomes 1 after sk_filter(), which bypassed the
> original check:
>
>         if (skb->len < sizeof(struct sctphdr) + sizeof(struct sctp_chunkhdr) +
>                        skb_transport_offset(skb))
> To handle this safely, a new check should be performed after sk_filter().
>
> Reported-by: syzbot+d101e12bccd4095460e7@...kaller.appspotmail.com
> Tested-by: syzbot+d101e12bccd4095460e7@...kaller.appspotmail.com
> Fixes: https://syzkaller.appspot.com/bug?extid=d101e12bccd4095460e7
> Suggested-by: Xin Long <lucien.xin@...il.com>
> Signed-off-by: Ranganath V N <vnranganath.20@...il.com>
Acked-by: Xin Long <lucien.xin@...il.com>

Thanks for the follow up.