Subject: Re: [syzbot] WARNING in mptcp_sendmsg_frag

From: Dan Carpenter <[email-masked]>
Date: Thu, 23 Sep 2021 17:19:42 +0300

On Wed, Sep 22, 2021 at 12:32:56PM +0200, Paolo Abeni wrote:
> 
> #syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> 
> The debug code helped a bit. It looks like we have singed/unsigned
> comparisons issue

There should be a static checker warning for these.  I have created one
in response to your email.  It turns out there are a couple other
instances of this bug in the same file.

net/mptcp/protocol.c:479 mptcp_subflow_could_cleanup() warn: unsigned subtraction: '(null)' use '!='
net/mptcp/protocol.c:909 mptcp_frag_can_collapse_to() warn: unsigned subtraction: 'pfrag->size - pfrag->offset' use '!='
net/mptcp/protocol.c:1319 mptcp_sendmsg_frag() warn: unsigned subtraction: 'info->size_goal - skb->len' use '!='

regards,
dan carpenter