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Date: Thu, 14 Mar 2019 18:40:38 +0100 From: Sabrina Dubroca <sd@...asysnail.net> To: Eric Dumazet <eric.dumazet@...il.com> Cc: netdev@...r.kernel.org, Jianlin Shi <jishi@...hat.com>, Stefano Brivio <sbrivio@...hat.com> Subject: Re: [PATCH net] net: enforce xmit_recursion for devices with a queue 2019-03-14, 07:56:10 -0700, Eric Dumazet wrote: > > > On 03/14/2019 07:15 AM, Sabrina Dubroca wrote: > > 2019-03-14, 05:58:03 -0700, Eric Dumazet wrote: > >> > >> > >> On 03/14/2019 03:15 AM, Sabrina Dubroca wrote: > >>> Commit 745e20f1b626 ("net: add a recursion limit in xmit path") > >>> introduced a recursion limit, but it only applies to devices without a > >>> queue. Virtual devices with a queue (either because they don't have > >>> the IFF_NO_QUEUE flag, or because the administrator added one) can > >>> still cause an unbounded recursion, via __dev_queue_xmit -> > >>> __dev_xmit_skb -> qdisc_run -> __qdisc_run -> qdisc_restart -> > >>> sch_direct_xmit -> dev_hard_start_xmit . Jianlin reported this in a > >>> setup with 16 gretap devices stacked on top of one another. > >>> > >>> This patch prevents the stack overflow by incrementing xmit_recursion in > >>> code paths that can call dev_hard_start_xmit() (like commit 745e20f1b626 > >>> did). If the recursion limit is exceeded, the packet is enqueued and the > >>> qdisc is scheduled. > >>> > >>> Reported-by: Jianlin Shi <jishi@...hat.com> > >>> Signed-off-by: Sabrina Dubroca <sd@...asysnail.net> > >>> Reviewed-by: Stefano Brivio <sbrivio@...hat.com> > >> > >> Hi Sabrina, thanks for the patch. > >> > >> Can't we detect this in the control path instead ? > > > > I don't see how. You could have a perfectly reasonable set of gretap > > devices that trigger this situation from simply reshuffling the IP > > addresses: > > > > gretap$x remote 1.1.$((x-1)).{1,2} > > (all those addresses set on a single veth device) > > > > Then you move those addresses to the corresponding device > > (1.1.${x}.{1,2} on gretap$x), and your machine crashes. > > > > If this only can be done with gretap, why gretap cant implement the protection, > outside of the fast path ? It's not just gretap. VXLAN will do the same as long as you add a qdisc. I expect other types of tunnels to behave like that. -- Sabrina
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