[PATCH net] udp: properly cope with csum errors

[Eric Dumazet]

From: Eric Dumazet <eduma...@google.com>

Dmitry reported that UDP sockets being destroyed would trigger the
WARN_ON(atomic_read(&sk->sk_rmem_alloc)); in inet_sock_destruct()

It turns out we do not properly destroy skb(s) that have wrong UDP
checksum.

Thanks again to syzkaller team.

Fixes : 7c13f97ffde6 ("udp: do fwd memory scheduling on dequeue")
Reported-by: Dmitry Vyukov <dvyu...@google.com>
Signed-off-by: Eric Dumazet <eduma...@google.com>
Cc: Paolo Abeni <pab...@redhat.com>
Cc: Hannes Frederic Sowa <han...@stressinduktion.org>
---
 include/net/sock.h  |    4 +++-
 net/core/datagram.c |    8 ++++++--
 net/ipv4/udp.c      |    2 +-
 net/ipv6/udp.c      |    2 +-
 4 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/include/net/sock.h b/include/net/sock.h
index f0e867f58722..c4f5e6fca17c 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -2006,7 +2006,9 @@ void sk_reset_timer(struct sock *sk, struct timer_list 
*timer,
 void sk_stop_timer(struct sock *sk, struct timer_list *timer);
 
 int __sk_queue_drop_skb(struct sock *sk, struct sk_buff *skb,
-                       unsigned int flags);
+                       unsigned int flags,
+                       void (*destructor)(struct sock *sk,
+                                          struct sk_buff *skb));
 int __sock_queue_rcv_skb(struct sock *sk, struct sk_buff *skb);
 int sock_queue_rcv_skb(struct sock *sk, struct sk_buff *skb);
 
diff --git a/net/core/datagram.c b/net/core/datagram.c
index 662bea587165..ea633342ab0d 100644
--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -332,7 +332,9 @@ void __skb_free_datagram_locked(struct sock *sk, struct 
sk_buff *skb, int len)
 EXPORT_SYMBOL(__skb_free_datagram_locked);
 
 int __sk_queue_drop_skb(struct sock *sk, struct sk_buff *skb,
-                       unsigned int flags)
+                       unsigned int flags,
+                       void (*destructor)(struct sock *sk,
+                                          struct sk_buff *skb))
 {
        int err = 0;
 
@@ -342,6 +344,8 @@ int __sk_queue_drop_skb(struct sock *sk, struct sk_buff 
*skb,
                if (skb == skb_peek(&sk->sk_receive_queue)) {
                        __skb_unlink(skb, &sk->sk_receive_queue);
                        atomic_dec(&skb->users);
+                       if (destructor)
+                               destructor(sk, skb);
                        err = 0;
                }
                spin_unlock_bh(&sk->sk_receive_queue.lock);
@@ -375,7 +379,7 @@ EXPORT_SYMBOL(__sk_queue_drop_skb);
 
 int skb_kill_datagram(struct sock *sk, struct sk_buff *skb, unsigned int flags)
 {
-       int err = __sk_queue_drop_skb(sk, skb, flags);
+       int err = __sk_queue_drop_skb(sk, skb, flags, NULL);
 
        kfree_skb(skb);
        sk_mem_reclaim_partial(sk);
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 1307a7c2e544..8aab7d78d25b 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1501,7 +1501,7 @@ int udp_recvmsg(struct sock *sk, struct msghdr *msg, 
size_t len, int noblock,
        return err;
 
 csum_copy_err:
-       if (!__sk_queue_drop_skb(sk, skb, flags)) {
+       if (!__sk_queue_drop_skb(sk, skb, flags, udp_skb_destructor)) {
                UDP_INC_STATS(sock_net(sk), UDP_MIB_CSUMERRORS, is_udplite);
                UDP_INC_STATS(sock_net(sk), UDP_MIB_INERRORS, is_udplite);
        }
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index 4d5c4eee4b3f..8990856f5101 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -441,7 +441,7 @@ int udpv6_recvmsg(struct sock *sk, struct msghdr *msg, 
size_t len,
        return err;
 
 csum_copy_err:
-       if (!__sk_queue_drop_skb(sk, skb, flags)) {
+       if (!__sk_queue_drop_skb(sk, skb, flags, udp_skb_destructor)) {
                if (is_udp4) {
                        UDP_INC_STATS(sock_net(sk),
                                      UDP_MIB_CSUMERRORS, is_udplite);