Re: [PATCH v2] decnet: dn_rtmsg: Improve input length sanitization in dnrmg_receive_user_skb

[Florian Westphal]

Mateusz Jurczyk <mjurczyk@xxxxxxxxxx> wrote:
> Verify that the length of the socket buffer is sufficient to cover the
> nlmsghdr structure before accessing the nlh->nlmsg_len field for further
> input sanitization. If the client only supplies 1-3 bytes of data in
> sk_buff, then nlh->nlmsg_len remains partially uninitialized and
> contains leftover memory from the corresponding kernel allocation.
> Operating on such data may result in indeterminate evaluation of the
> nlmsg_len < sizeof(*nlh) expression.
> 
> The bug was discovered by a runtime instrumentation designed to detect
> use of uninitialized memory in the kernel. The patch prevents this and
> other similar tools (e.g. KMSAN) from flagging this behavior in the future.

Instead of changing all the internal users wouldn't it be better
to add this check once in netlink_unicast_kernel?