From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mark Rutland Subject: Re: v4.14-rc2/arm64 kernel BUG at net/core/skbuff.c:2626 Date: Mon, 2 Oct 2017 16:01:57 +0100 Message-ID: <20171002150156.GC21696@leverpostej> References: <20171002104947.GE20737@leverpostej> <20171002142156.GB21696@leverpostej> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: LKML , netdev , linux-arm-kernel@lists.infradead.org, syzkaller , "David S. Miller" , Willem de Bruijn To: Eric Dumazet Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Mon, Oct 02, 2017 at 07:42:17AM -0700, Eric Dumazet wrote: > On Mon, Oct 2, 2017 at 7:21 AM, Mark Rutland wrote: > > Just to check I've understood correctly, are you suggesting that the > > IPv4 code should also check the dev->mtu against a IP_MIN_MTU (which > > doesn't seem to exist today)? > > We have plenty of places this is checked. > > For example, trying to set MTU < 68 usually removes IPv4 addresses and routes. > > Problem is : these checks are not fool proof yet. > > ( Only the admin was supposed to play these games ) Sorry, I meant that there was no constant called IP_MIN_MTU, and I was just looking at the sites fixed up by c780a049f9bf4423. I appreciate given that this requires admin privileges it's not exactly high priority. I didn't mean for the above to sound like some kind of accusation! > > Otherwise, I do spot another potential issue. The writer side (e.g. most > > net_device::ndo_change_mtu implementations and the __dev_set_mtu() > > fallback) doesn't use WRITE_ONCE(). > > It does not matter how many strange values can be observed by the reader : > We must be fool proof anyway from reader point of view, so the > WRITE_ONCE() is not strictly needed. Ok. If we expect to always check somewhere on the reader side I guess that makes sense. Thanks, Mark.