Subject: Re: [PATCH net] netdevsim: Initialize all fields of ip header when building dummy sk_buff

From: Breno Leitao <[email-masked]>
Date: Tue, 21 Apr 2026 01:19:25 -0700

On Tue, Apr 21, 2026 at 10:37:38AM +0300, Nikola Z. Ivanov wrote:
> Syzbot reports a KMSAN uninit-value originating from
> nsim_dev_trap_skb_build, with the allocation also
> being performed in the same function.
> 
> The cause of the KMSAN warning is a missing assignment of
> the tos and id fields of the ip header.
> 
> Fix this by calling skb_put_zero instead of skb_put to
> guarantee null initialization.

> Additionally remove the now redundant zero assignments
> and reorder the remaining ones so that they more closely
> match the order of the fields as they appear in the ip header.
> 
> Closes: https://syzkaller.appspot.com/bug?extid=23d7fcd204e3837866ff

How do you check in the report above that the missig un-initialized
fields are "tos" and "id"?

Thanks for the fix,
--breno