Subject: Re: [PATCH net] ppp: ensure minimum packet size in ppp_write()

From: Guillaume Nault <[email-masked]>
Date: Wed, 5 Jan 2022 14:19:29 +0100

On Wed, Jan 05, 2022 at 03:48:42AM -0800, Eric Dumazet wrote:
> From: Eric Dumazet <[email-masked]>
> 
> It seems pretty clear ppp layer assumed user space
> would always be kind to provide enough data
> in their write() to a ppp device.
> 
> This patch makes sure user provides at least
> 2 bytes.
> 
> It adds PPP_PROTO_LEN macro that could replace
> in net-next many occurrences of hard-coded 2 value.

The PPP header can be compressed to only 1 byte, but since 2 bytes is
assumed in several parts of the code, rejecting such packets in
ppp_xmit() is probably the best we can do.

Acked-by: Guillaume Nault <[email-masked]>