On Tue, 13 Oct 2020 19:18:48 +0200 Kleber Sacilotto de Souza wrote: > From: Thadeu Lima de Souza Cascardo <cascardo@xxxxxxxxxxxxx> > > When dccps_hc_tx_ccid is freed, ccid timers may still trigger. The reason > del_timer_sync can't be used is because this relies on keeping a reference > to struct sock. But as we keep a pointer to dccps_hc_tx_ccid and free that > during disconnect, the timer should really belong to struct dccp_sock. > > This addresses CVE-2020-16119. > > Fixes: 839a6094140a (net: dccp: Convert timers to use timer_setup()) > Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@xxxxxxxxxxxxx> > Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@xxxxxxxxxxxxx> I've been mulling over this fix. The layering violation really doesn't sit well. We're reusing the timer object. What if we are really unlucky, the fires and gets blocked by a cosmic ray just as it's about to try to lock the socket, then user manages to reconnect, and timer starts again. Potentially with a different CCID algo altogether? Is disconnect ever called under the BH lock? Maybe plumb a bool argument through to ccid*_hc_tx_exit() and do a sk_stop_timer_sync() when called from disconnect()? Or do refcounting on ccid_priv so that the timer holds both the socket and the priv?
