packet: dont call sleeping functions while holding rcu_read_lock()

commit 654d1f8a019dfa06d (packet: less dev_put() calls)
introduced a problem, calling potentially sleeping functions from a
rcu_read_lock() protected section.

Fix this by releasing lock before the sock_wmalloc()/memcpy_fromiovec() calls.

After skb allocation and copy from user space, we redo device
lookup and appropriate tests.

Reported-and-tested-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 31 insertions, 40 deletions

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 020562164b5..e0516a22be2 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -415,7 +415,7 @@ static int packet_sendmsg_spkt(struct kiocb *iocb, struct socket *sock,
 {
         struct sock *sk = sock->sk;
         struct sockaddr_pkt *saddr = (struct sockaddr_pkt *)msg->msg_name;
-        struct sk_buff *skb;
+        struct sk_buff *skb = NULL;
         struct net_device *dev;
         __be16 proto = 0;
         int err;
@@ -437,6 +437,7 @@ static int packet_sendmsg_spkt(struct kiocb *iocb, struct socket *sock,
          */
 
         saddr->spkt_device[13] = 0;
+retry:
         rcu_read_lock();
         dev = dev_get_by_name_rcu(sock_net(sk), saddr->spkt_device);
         err = -ENODEV;
@@ -456,58 +457,48 @@ static int packet_sendmsg_spkt(struct kiocb *iocb, struct socket *sock,
         if (len > dev->mtu + dev->hard_header_len)
                 goto out_unlock;
 
-        err = -ENOBUFS;
-        skb = sock_wmalloc(sk, len + LL_RESERVED_SPACE(dev), 0, GFP_KERNEL);
-
-        /*
-         * If the write buffer is full, then tough. At this level the user
-         * gets to deal with the problem - do your own algorithmic backoffs.
-         * That's far more flexible.
-         */
-
-        if (skb == NULL)
-                goto out_unlock;
-
-        /*
-         *      Fill it in
-         */
-
-        /* FIXME: Save some space for broken drivers that write a
-         * hard header at transmission time by themselves. PPP is the
-         * notable one here. This should really be fixed at the driver level.
-         */
-        skb_reserve(skb, LL_RESERVED_SPACE(dev));
-        skb_reset_network_header(skb);
-
-        /* Try to align data part correctly */
-        if (dev->header_ops) {
-                skb->data -= dev->hard_header_len;
-                skb->tail -= dev->hard_header_len;
-                if (len < dev->hard_header_len)
-                        skb_reset_network_header(skb);
+        if (!skb) {
+                size_t reserved = LL_RESERVED_SPACE(dev);
+                unsigned int hhlen = dev->header_ops ? dev->hard_header_len : 0;
+
+                rcu_read_unlock();
+                skb = sock_wmalloc(sk, len + reserved, 0, GFP_KERNEL);
+                if (skb == NULL)
+                        return -ENOBUFS;
+                /* FIXME: Save some space for broken drivers that write a hard
+                 * header at transmission time by themselves. PPP is the notable
+                 * one here. This should really be fixed at the driver level.
+                 */
+                skb_reserve(skb, reserved);
+                skb_reset_network_header(skb);
+
+                /* Try to align data part correctly */
+                if (hhlen) {
+                        skb->data -= hhlen;
+                        skb->tail -= hhlen;
+                        if (len < hhlen)
+                                skb_reset_network_header(skb);
+                }
+                err = memcpy_fromiovec(skb_put(skb, len), msg->msg_iov, len);
+                if (err)
+                        goto out_free;
+                goto retry;
         }
 
-        /* Returns -EFAULT on error */
-        err = memcpy_fromiovec(skb_put(skb, len), msg->msg_iov, len);
+
         skb->protocol = proto;
         skb->dev = dev;
         skb->priority = sk->sk_priority;
         skb->mark = sk->sk_mark;
-        if (err)
-                goto out_free;
-
-        /*
-         *      Now send it
-         */
 
         dev_queue_xmit(skb);
         rcu_read_unlock();
         return len;
 
-out_free:
-        kfree_skb(skb);
 out_unlock:
         rcu_read_unlock();
+out_free:
+        kfree_skb(skb);
         return err;
 }