From: Guillaume Nault <gnault@redhat.com>
To: James Carlson <carlsonj@workingcode.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>,
"David S . Miller" <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>, netdev <netdev@vger.kernel.org>,
Eric Dumazet <edumazet@google.com>,
Paul Mackerras <paulus@samba.org>,
linux-ppp@vger.kernel.org, syzbot <syzkaller@googlegroups.com>
Subject: Re: [PATCH net] ppp: ensure minimum packet size in ppp_write()
Date: Wed, 5 Jan 2022 17:29:54 +0100 [thread overview]
Message-ID: <20220105162954.GB17823@pc-1.home> (raw)
In-Reply-To: <dbde2a45-a7dd-0e8a-d04c-233f69631885@workingcode.com>
On Wed, Jan 05, 2022 at 10:30:09AM -0500, James Carlson wrote:
> On 1/5/22 08:19, Guillaume Nault wrote:
> > On Wed, Jan 05, 2022 at 03:48:42AM -0800, Eric Dumazet wrote:
> >> From: Eric Dumazet <edumazet@google.com>
> >>
> >> 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.
>
> The only ones that can be compressed are those less than 0x0100, which
> are (intentionally) all network layer protocols. We should be getting
> only control protocol messages though the user-space interface, not
> network layer, so I'd say it's not just the best we can do, but indeed
> the right thing to do by design.
Well, I know of at least one implementation that used to transmit data
by writing on ppp unit file descriptors. That was a hack to work around
some other problems. Not a beautiful one, but it worked.
next prev parent reply other threads:[~2022-01-05 16:30 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-05 11:48 [PATCH net] ppp: ensure minimum packet size in ppp_write() Eric Dumazet
2022-01-05 13:19 ` Guillaume Nault
2022-01-05 15:30 ` James Carlson
2022-01-05 16:29 ` Guillaume Nault [this message]
2022-01-05 16:35 ` James Carlson
2022-01-05 17:37 ` Guillaume Nault
2022-01-06 12:40 ` patchwork-bot+netdevbpf
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