inet: fix possible panic in reqsk_queue_unlink()

[ 3897.923145] BUG: unable to handle kernel NULL pointer dereference at
 0000000000000080
[ 3897.931025] IP: [<ffffffffa9f27686>] reqsk_timer_handler+0x1a6/0x243

There is a race when reqsk_timer_handler() and tcp_check_req() call
inet_csk_reqsk_queue_unlink() on the same req at the same time.

Before commit fa76ce7328b2 ("inet: get rid of central tcp/dccp listener
timer"), listener spinlock was held and race could not happen.

To solve this bug, we change reqsk_queue_unlink() to not assume req
must be found, and we return a status, to conditionally release a
refcount on the request sock.

This also means tcp_check_req() in non fastopen case might or not
consume req refcount, so tcp_v6_hnd_req() & tcp_v4_hnd_req() have
to properly handle this.

(Same remark for dccp_check_req() and its callers)

inet_csk_reqsk_queue_drop() is now too big to be inlined, as it is
called 4 times in tcp and 3 times in dccp.

Fixes: fa76ce7328b2 ("inet: get rid of central tcp/dccp listener timer")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/net/inet_connection_sock.h b/include/net/inet_connection_sock.h
index 7b5887c..48a8158 100644 (file)
--- a/include/net/inet_connection_sock.h
+++ b/include/net/inet_connection_sock.h
@@ -279,12 +279,6 @@ static inline void inet_csk_reqsk_queue_add(struct sock *sk,
 void inet_csk_reqsk_queue_hash_add(struct sock *sk, struct request_sock *req,
                                   unsigned long timeout);
 
-static inline void inet_csk_reqsk_queue_removed(struct sock *sk,
-                                               struct request_sock *req)
-{
-       reqsk_queue_removed(&inet_csk(sk)->icsk_accept_queue, req);
-}
-
 static inline void inet_csk_reqsk_queue_added(struct sock *sk,
                                              const unsigned long timeout)
 {
@@ -306,19 +300,7 @@ static inline int inet_csk_reqsk_queue_is_full(const struct sock *sk)
        return reqsk_queue_is_full(&inet_csk(sk)->icsk_accept_queue);
 }
 
-static inline void inet_csk_reqsk_queue_unlink(struct sock *sk,
-                                              struct request_sock *req)
-{
-       reqsk_queue_unlink(&inet_csk(sk)->icsk_accept_queue, req);
-}
-
-static inline void inet_csk_reqsk_queue_drop(struct sock *sk,
-                                            struct request_sock *req)
-{
-       inet_csk_reqsk_queue_unlink(sk, req);
-       inet_csk_reqsk_queue_removed(sk, req);
-       reqsk_put(req);
-}
+void inet_csk_reqsk_queue_drop(struct sock *sk, struct request_sock *req);
 
 void inet_csk_destroy_sock(struct sock *sk);
 void inet_csk_prepare_forced_close(struct sock *sk);

diff --git a/include/net/request_sock.h b/include/net/request_sock.h
index fe41f3c..9f4265c 100644 (file)
--- a/include/net/request_sock.h
+++ b/include/net/request_sock.h
@@ -212,24 +212,6 @@ static inline int reqsk_queue_empty(struct request_sock_queue *queue)
        return queue->rskq_accept_head == NULL;
 }
 
-static inline void reqsk_queue_unlink(struct request_sock_queue *queue,
-                                     struct request_sock *req)
-{
-       struct listen_sock *lopt = queue->listen_opt;
-       struct request_sock **prev;
-
-       spin_lock(&queue->syn_wait_lock);
-
-       prev = &lopt->syn_table[req->rsk_hash];
-       while (*prev != req)
-               prev = &(*prev)->dl_next;
-       *prev = req->dl_next;
-
-       spin_unlock(&queue->syn_wait_lock);
-       if (del_timer(&req->rsk_timer))
-               reqsk_put(req);
-}
-
 static inline void reqsk_queue_add(struct request_sock_queue *queue,
                                   struct request_sock *req,
                                   struct sock *parent,

diff --git a/net/dccp/ipv4.c b/net/dccp/ipv4.c
index 2b4f21d..ccf4c56 100644 (file)
--- a/net/dccp/ipv4.c
+++ b/net/dccp/ipv4.c
@@ -453,7 +453,8 @@ static struct sock *dccp_v4_hnd_req(struct sock *sk, struct sk_buff *skb)
                                                       iph->saddr, iph->daddr);
        if (req) {
                nsk = dccp_check_req(sk, skb, req);
-               reqsk_put(req);
+               if (!nsk)
+                       reqsk_put(req);
                return nsk;
        }
        nsk = inet_lookup_established(sock_net(sk), &dccp_hashinfo,

diff --git a/net/dccp/ipv6.c b/net/dccp/ipv6.c
index 9d05510..5165571 100644 (file)
--- a/net/dccp/ipv6.c
+++ b/net/dccp/ipv6.c
@@ -301,7 +301,8 @@ static struct sock *dccp_v6_hnd_req(struct sock *sk,struct sk_buff *skb)
                                   &iph->daddr, inet6_iif(skb));
        if (req) {
                nsk = dccp_check_req(sk, skb, req);
-               reqsk_put(req);
+               if (!nsk)
+                       reqsk_put(req);
                return nsk;
        }
        nsk = __inet6_lookup_established(sock_net(sk), &dccp_hashinfo,

diff --git a/net/dccp/minisocks.c b/net/dccp/minisocks.c
index 5f56666..30addee 100644 (file)
--- a/net/dccp/minisocks.c
+++ b/net/dccp/minisocks.c
@@ -186,8 +186,7 @@ struct sock *dccp_check_req(struct sock *sk, struct sk_buff *skb,
        if (child == NULL)
                goto listen_overflow;
 
-       inet_csk_reqsk_queue_unlink(sk, req);
-       inet_csk_reqsk_queue_removed(sk, req);
+       inet_csk_reqsk_queue_drop(sk, req);
        inet_csk_reqsk_queue_add(sk, req, child);
 out:
        return child;

diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index 5c3dd62..8976ca4 100644 (file)
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -564,6 +564,40 @@ int inet_rtx_syn_ack(struct sock *parent, struct request_sock *req)
 }
 EXPORT_SYMBOL(inet_rtx_syn_ack);
 
+/* return true if req was found in the syn_table[] */
+static bool reqsk_queue_unlink(struct request_sock_queue *queue,
+                              struct request_sock *req)
+{
+       struct listen_sock *lopt = queue->listen_opt;
+       struct request_sock **prev;
+       bool found = false;
+
+       spin_lock(&queue->syn_wait_lock);
+
+       for (prev = &lopt->syn_table[req->rsk_hash]; *prev != NULL;
+            prev = &(*prev)->dl_next) {
+               if (*prev == req) {
+                       *prev = req->dl_next;
+                       found = true;
+                       break;
+               }
+       }
+
+       spin_unlock(&queue->syn_wait_lock);
+       if (del_timer(&req->rsk_timer))
+               reqsk_put(req);
+       return found;
+}
+
+void inet_csk_reqsk_queue_drop(struct sock *sk, struct request_sock *req)
+{
+       if (reqsk_queue_unlink(&inet_csk(sk)->icsk_accept_queue, req)) {
+               reqsk_queue_removed(&inet_csk(sk)->icsk_accept_queue, req);
+               reqsk_put(req);
+       }
+}
+EXPORT_SYMBOL(inet_csk_reqsk_queue_drop);
+
 static void reqsk_timer_handler(unsigned long data)
 {
        struct request_sock *req = (struct request_sock *)data;

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 3571f2b..fc1c658 100644 (file)
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1348,7 +1348,8 @@ static struct sock *tcp_v4_hnd_req(struct sock *sk, struct sk_buff *skb)
        req = inet_csk_search_req(sk, th->source, iph->saddr, iph->daddr);
        if (req) {
                nsk = tcp_check_req(sk, skb, req, false);
-               reqsk_put(req);
+               if (!nsk)
+                       reqsk_put(req);
                return nsk;
        }
 

diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 63d6311..e5d7649 100644 (file)
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -755,10 +755,11 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
        if (!child)
                goto listen_overflow;
 
-       inet_csk_reqsk_queue_unlink(sk, req);
-       inet_csk_reqsk_queue_removed(sk, req);
-
+       inet_csk_reqsk_queue_drop(sk, req);
        inet_csk_reqsk_queue_add(sk, req, child);
+       /* Warning: caller must not call reqsk_put(req);
+        * child stole last reference on it.
+        */
        return child;
 
 listen_overflow:

diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index ad51df8..b6575d6 100644 (file)
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -946,7 +946,8 @@ static struct sock *tcp_v6_hnd_req(struct sock *sk, struct sk_buff *skb)
                                   &ipv6_hdr(skb)->daddr, tcp_v6_iif(skb));
        if (req) {
                nsk = tcp_check_req(sk, skb, req, false);
-               reqsk_put(req);
+               if (!nsk)
+                       reqsk_put(req);
                return nsk;
        }
        nsk = __inet6_lookup_established(sock_net(sk), &tcp_hashinfo,