From 02efdff7e209859c2755ebe93b3bd0e3d40123ab Mon Sep 17 00:00:00 2001 From: Florian Westphal Date: Tue, 9 Aug 2016 12:16:05 +0200 Subject: [PATCH] xfrm: state: use atomic_inc_not_zero to increment refcount Once xfrm_state_lookup_byaddr no longer acquires the state lock another cpu might be freeing the state entry at the same time. To detect this we use atomic_inc_not_zero, we then signal -EAGAIN to caller in case our result was stale. Signed-off-by: Florian Westphal Signed-off-by: Steffen Klassert --- net/xfrm/xfrm_state.c | 21 ++++++++++++++++----- 1 file changed, 16 insertions(+), 5 deletions(-) diff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c index 904ab4d4ac05..84c1db6254d5 100644 --- a/net/xfrm/xfrm_state.c +++ b/net/xfrm/xfrm_state.c @@ -37,6 +37,11 @@ static unsigned int xfrm_state_hashmax __read_mostly = 1 * 1024 * 1024; +static inline bool xfrm_state_hold_rcu(struct xfrm_state __rcu *x) +{ + return atomic_inc_not_zero(&x->refcnt); +} + static inline unsigned int xfrm_dst_hash(struct net *net, const xfrm_address_t *daddr, const xfrm_address_t *saddr, @@ -668,7 +673,8 @@ static struct xfrm_state *__xfrm_state_lookup(struct net *net, u32 mark, if ((mark & x->mark.m) != x->mark.v) continue; - xfrm_state_hold(x); + if (!xfrm_state_hold_rcu(x)) + continue; return x; } @@ -692,7 +698,8 @@ static struct xfrm_state *__xfrm_state_lookup_byaddr(struct net *net, u32 mark, if ((mark & x->mark.m) != x->mark.v) continue; - xfrm_state_hold(x); + if (!xfrm_state_hold_rcu(x)) + continue; return x; } @@ -871,10 +878,14 @@ found: } } out: - if (x) - xfrm_state_hold(x); - else + if (x) { + if (!xfrm_state_hold_rcu(x)) { + *err = -EAGAIN; + x = NULL; + } + } else { *err = acquire_in_progress ? -EAGAIN : error; + } spin_unlock_bh(&net->xfrm.xfrm_state_lock); if (to_put) xfrm_state_put(to_put);