tcp: fix MD5 (RFC2385) support

TCP MD5 support uses percpu data for temporary storage. It currently
disables preemption so that same storage cannot be reclaimed by another
thread on same cpu.

We also have to make sure a softirq handler wont try to use also same
context. Various bug reports demonstrated corruptions.

Fix is to disable preemption and BH.

Reported-by: Bhaskar Dutta <bhaskie@gmail.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/tcp.h

@@ -1197,30 +1197,15 @@ extern int			tcp_v4_md5_do_del(struct sock *sk,
 extern struct tcp_md5sig_pool * __percpu *tcp_alloc_md5sig_pool(struct sock *);
 extern void			tcp_free_md5sig_pool(void);
 
-extern struct tcp_md5sig_pool	*__tcp_get_md5sig_pool(int cpu);
-extern void			__tcp_put_md5sig_pool(void);
+extern struct tcp_md5sig_pool	*tcp_get_md5sig_pool(void);
+extern void			tcp_put_md5sig_pool(void);
+
 extern int tcp_md5_hash_header(struct tcp_md5sig_pool *, struct tcphdr *);
 extern int tcp_md5_hash_skb_data(struct tcp_md5sig_pool *, struct sk_buff *,
 				 unsigned header_len);
 extern int tcp_md5_hash_key(struct tcp_md5sig_pool *hp,
 			    struct tcp_md5sig_key *key);
 
-static inline
-struct tcp_md5sig_pool		*tcp_get_md5sig_pool(void)
-{
-	int cpu = get_cpu();
-	struct tcp_md5sig_pool *ret = __tcp_get_md5sig_pool(cpu);
-	if (!ret)
-		put_cpu();
-	return ret;
-}
-
-static inline void		tcp_put_md5sig_pool(void)
-{
-	__tcp_put_md5sig_pool();
-	put_cpu();
-}
-
 /* write queue abstraction */
 static inline void tcp_write_queue_purge(struct sock *sk)
 {

net/ipv4/tcp.c

@@ -2839,7 +2839,6 @@ static void __tcp_free_md5sig_pool(struct tcp_md5sig_pool * __percpu *pool)
 			if (p->md5_desc.tfm)
 				crypto_free_hash(p->md5_desc.tfm);
 			kfree(p);
-			p = NULL;
 		}
 	}
 	free_percpu(pool);
@@ -2937,25 +2936,40 @@ retry:
 
 EXPORT_SYMBOL(tcp_alloc_md5sig_pool);
 
-struct tcp_md5sig_pool *__tcp_get_md5sig_pool(int cpu)
+
+/**
+ *	tcp_get_md5sig_pool - get md5sig_pool for this user
+ *
+ *	We use percpu structure, so if we succeed, we exit with preemption
+ *	and BH disabled, to make sure another thread or softirq handling
+ *	wont try to get same context.
+ */
+struct tcp_md5sig_pool *tcp_get_md5sig_pool(void)
 {
 	struct tcp_md5sig_pool * __percpu *p;
-	spin_lock_bh(&tcp_md5sig_pool_lock);
+
+	local_bh_disable();
+
+	spin_lock(&tcp_md5sig_pool_lock);
 	p = tcp_md5sig_pool;
 	if (p)
 		tcp_md5sig_users++;
-	spin_unlock_bh(&tcp_md5sig_pool_lock);
-	return (p ? *per_cpu_ptr(p, cpu) : NULL);
-}
+	spin_unlock(&tcp_md5sig_pool_lock);
+
+	if (p)
+		return *per_cpu_ptr(p, smp_processor_id());
 
-EXPORT_SYMBOL(__tcp_get_md5sig_pool);
+	local_bh_enable();
+	return NULL;
+}
+EXPORT_SYMBOL(tcp_get_md5sig_pool);
 
-void __tcp_put_md5sig_pool(void)
+void tcp_put_md5sig_pool(void)
 {
+	local_bh_enable();
 	tcp_free_md5sig_pool();
 }
-
-EXPORT_SYMBOL(__tcp_put_md5sig_pool);
+EXPORT_SYMBOL(tcp_put_md5sig_pool);
 
 int tcp_md5_hash_header(struct tcp_md5sig_pool *hp,
 			struct tcphdr *th)