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Date: Thu, 14 Mar 2019 15:15:05 +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, 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. -- Sabrina
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