Re: [PATCH] xfrm: policy: Restructure RCU-read locking in xfrm_sk_policy_lookup
From: Steffen Klassert <steffen.klassert@secunet.com>
Date: 2021-06-21 08:29:55
Also in:
linux-rt-users, lkml, netdev
On Fri, Jun 18, 2021 at 04:11:01PM +0200, Varad Gautam wrote:
Commit "xfrm: policy: Read seqcount outside of rcu-read side in
xfrm_policy_lookup_bytype" [Linked] resolved a locking bug in
xfrm_policy_lookup_bytype that causes an RCU reader-writer deadlock on
the mutex wrapped by xfrm_policy_hash_generation on PREEMPT_RT since
77cc278f7b20 ("xfrm: policy: Use sequence counters with associated
lock").
However, xfrm_sk_policy_lookup can still reach xfrm_policy_lookup_bytype
while holding rcu_read_lock(), as:
xfrm_sk_policy_lookup()
rcu_read_lock()
security_xfrm_policy_lookup()
xfrm_policy_lookup()Hm, I don't see that call chain. security_xfrm_policy_lookup() calls a hook with the name xfrm_policy_lookup. The only LSM that has registered a function to that hook is selinux. It registers selinux_xfrm_policy_lookup() and I don't see how we can call xfrm_policy_lookup() from there. Did you actually trigger that bug?