tcp: avoid infinite loop in tcp_splice_read()

[ Upstream commit ccf7abb93af09ad0868ae9033d1ca8108bdaec82 ]

Splicing from TCP socket is vulnerable when a packet with URG flag is
received and stored into receive queue.

__tcp_splice_read() returns 0, and sk_wait_data() immediately
returns since there is the problematic skb in queue.

This is a nice way to burn cpu (aka infinite loop) and trigger
soft lockups.

Again, this gem was found by syzkaller tool.

Fixes: 9c55e01c0cc8 ("[TCP]: Splice receive support.")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Dmitry Vyukov  <dvyukov@google.com>
Cc: Willy Tarreau <w@1wt.eu>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 814af89c1bd3..6a90a0e130dc 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -772,6 +772,12 @@ ssize_t tcp_splice_read(struct socket *sock, loff_t *ppos,
                                 ret = -EAGAIN;
                                 break;
                         }
+                        /* if __tcp_splice_read() got nothing while we have
+                         * an skb in receive queue, we do not want to loop.
+                         * This might happen with URG data.
+                         */
+                        if (!skb_queue_empty(&sk->sk_receive_queue))
+                                break;
                         sk_wait_data(sk, &timeo, NULL);
                         if (signal_pending(current)) {
                                 ret = sock_intr_errno(timeo);