[IPV4] ip_fragment: Always compute hash with ipfrag_lock held.

Otherwise we could compute an inaccurate hash due to the
random seed changing.

Noticed by Zach Brown and patch is based upon some feedback
from Herbert Xu.

Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 10 insertions, 5 deletions

diff --git a/net/ipv4/ip_fragment.c b/net/ipv4/ip_fragment.c
index 2a8adda15e11..da734c439179 100644
--- a/net/ipv4/ip_fragment.c
+++ b/net/ipv4/ip_fragment.c
@@ -304,13 +304,17 @@ out:
 
 /* Creation primitives. */
 
-static struct ipq *ip_frag_intern(unsigned int hash, struct ipq *qp_in)
+static struct ipq *ip_frag_intern(struct ipq *qp_in)
 {
         struct ipq *qp;
 #ifdef CONFIG_SMP
         struct hlist_node *n;
 #endif
+        unsigned int hash;
+
         write_lock(&ipfrag_lock);
+        hash = ipqhashfn(qp_in->id, qp_in->saddr, qp_in->daddr,
+                         qp_in->protocol);
 #ifdef CONFIG_SMP
         /* With SMP race we have to recheck hash table, because
          * such entry could be created on other cpu, while we
@@ -345,7 +349,7 @@ static struct ipq *ip_frag_intern(unsigned int hash, struct ipq *qp_in)
 }
 
 /* Add an entry to the 'ipq' queue for a newly received IP datagram. */
-static struct ipq *ip_frag_create(unsigned hash, struct iphdr *iph, u32 user)
+static struct ipq *ip_frag_create(struct iphdr *iph, u32 user)
 {
         struct ipq *qp;
 
@@ -371,7 +375,7 @@ static struct ipq *ip_frag_create(unsigned hash, struct iphdr *iph, u32 user)
         spin_lock_init(&qp->lock);
         atomic_set(&qp->refcnt, 1);
 
-        return ip_frag_intern(hash, qp);
+        return ip_frag_intern(qp);
 
 out_nomem:
         LIMIT_NETDEBUG(KERN_ERR "ip_frag_create: no memory left !\n");
@@ -387,11 +391,12 @@ static inline struct ipq *ip_find(struct iphdr *iph, u32 user)
         __u32 saddr = iph->saddr;
         __u32 daddr = iph->daddr;
         __u8 protocol = iph->protocol;
-        unsigned int hash = ipqhashfn(id, saddr, daddr, protocol);
+        unsigned int hash;
         struct ipq *qp;
         struct hlist_node *n;
 
         read_lock(&ipfrag_lock);
+        hash = ipqhashfn(id, saddr, daddr, protocol);
         hlist_for_each_entry(qp, n, &ipq_hash[hash], list) {
                 if(qp->id == id         &&
                    qp->saddr == saddr   &&
@@ -405,7 +410,7 @@ static inline struct ipq *ip_find(struct iphdr *iph, u32 user)
         }
         read_unlock(&ipfrag_lock);
 
-        return ip_frag_create(hash, iph, user);
+        return ip_frag_create(iph, user);
 }
 
 /* Is the fragment too far ahead to be part of ipq? */