inet fragments: fix race between inet_frag_find and inet_frag_secret_rebuild

The problem is that while we work w/o the inet_frags.lock even
read-locked the secret rebuild timer may occur (on another CPU, since
BHs are still disabled in the inet_frag_find) and change the rnd seed
for ipv4/6 fragments.

It was caused by my patch fd9e63544cac30a34c951f0ec958038f0529e244
([INET]: Omit double hash calculations in xxx_frag_intern) late 
in the 2.6.24 kernel, so this should probably be queued to -stable.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 11 insertions, 5 deletions

diff --git a/net/ipv4/inet_fragment.c b/net/ipv4/inet_fragment.c
index 4ed429bd5951..0546a0bc97ea 100644
--- a/net/ipv4/inet_fragment.c
+++ b/net/ipv4/inet_fragment.c
@@ -192,14 +192,21 @@ EXPORT_SYMBOL(inet_frag_evictor);
 
 static struct inet_frag_queue *inet_frag_intern(struct netns_frags *nf,
                 struct inet_frag_queue *qp_in, struct inet_frags *f,
-                unsigned int hash, void *arg)
+                void *arg)
 {
         struct inet_frag_queue *qp;
 #ifdef CONFIG_SMP
         struct hlist_node *n;
 #endif
+        unsigned int hash;
 
         write_lock(&f->lock);
+        /*
+         * While we stayed w/o the lock other CPU could update
+         * the rnd seed, so we need to re-calculate the hash
+         * chain. Fortunatelly the qp_in can be used to get one.
+         */
+        hash = f->hashfn(qp_in);
 #ifdef CONFIG_SMP
         /* With SMP race we have to recheck hash table, because
          * such entry could be created on other cpu, while we
@@ -247,7 +254,7 @@ static struct inet_frag_queue *inet_frag_alloc(struct netns_frags *nf,
 }
 
 static struct inet_frag_queue *inet_frag_create(struct netns_frags *nf,
-                struct inet_frags *f, void *arg, unsigned int hash)
+                struct inet_frags *f, void *arg)
 {
         struct inet_frag_queue *q;
 
@@ -255,7 +262,7 @@ static struct inet_frag_queue *inet_frag_create(struct netns_frags *nf,
         if (q == NULL)
                 return NULL;
 
-        return inet_frag_intern(nf, q, f, hash, arg);
+        return inet_frag_intern(nf, q, f, arg);
 }
 
 struct inet_frag_queue *inet_frag_find(struct netns_frags *nf,
@@ -264,7 +271,6 @@ struct inet_frag_queue *inet_frag_find(struct netns_frags *nf,
         struct inet_frag_queue *q;
         struct hlist_node *n;
 
-        read_lock(&f->lock);
         hlist_for_each_entry(q, n, &f->hash[hash], list) {
                 if (q->net == nf && f->match(q, key)) {
                         atomic_inc(&q->refcnt);
@@ -274,6 +280,6 @@ struct inet_frag_queue *inet_frag_find(struct netns_frags *nf,
         }
         read_unlock(&f->lock);
 
-        return inet_frag_create(nf, f, key, hash);
+        return inet_frag_create(nf, f, key);
 }
 EXPORT_SYMBOL(inet_frag_find);