tcp: tcp_fragment() should apply sane memory limits

commit f070ef2ac66716357066b683fb0baf55f8191a2e upstream.

Jonathan Looney reported that a malicious peer can force a sender
to fragment its retransmit queue into tiny skbs, inflating memory
usage and/or overflow 32bit counters.

TCP allows an application to queue up to sk_sndbuf bytes,
so we need to give some allowance for non malicious splitting
of retransmit queue.

A new SNMP counter is added to monitor how many times TCP
did not allow to split an skb if the allowance was exceeded.

Note that this counter might increase in the case applications
use SO_SNDBUF socket option to lower sk_sndbuf.

CVE-2019-11478 : tcp_fragment, prevent fragmenting a packet when the
	socket is already using more than half the allowed space

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Jonathan Looney <jtl@netflix.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Acked-by: Yuchung Cheng <ycheng@google.com>
Reviewed-by: Tyler Hicks <tyhicks@canonical.com>
Cc: Bruce Curtis <brucec@netflix.com>
Cc: Jonathan Lemon <jonathan.lemon@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/include/uapi/linux/snmp.h b/include/uapi/linux/snmp.h
index f80135e5feaa886000009db6dff75b2bc2d637b2..abae27c3001c3d1c8295d8012628361cafc6de9c 100644 (file)
--- a/include/uapi/linux/snmp.h
+++ b/include/uapi/linux/snmp.h
@@ -282,6 +282,7 @@ enum
        LINUX_MIB_TCPACKCOMPRESSED,             /* TCPAckCompressed */
        LINUX_MIB_TCPZEROWINDOWDROP,            /* TCPZeroWindowDrop */
        LINUX_MIB_TCPRCVQDROP,                  /* TCPRcvQDrop */
+       LINUX_MIB_TCPWQUEUETOOBIG,              /* TCPWqueueTooBig */
        __LINUX_MIB_MAX
 };
 

diff --git a/net/ipv4/proc.c b/net/ipv4/proc.c
index 70289682a6701438aed99a00a9705c39fa4394d3..eab5c02da8ae84a9c2fcc4a1d0c594ff562755b1 100644 (file)
--- a/net/ipv4/proc.c
+++ b/net/ipv4/proc.c
@@ -290,6 +290,7 @@ static const struct snmp_mib snmp4_net_list[] = {
        SNMP_MIB_ITEM("TCPAckCompressed", LINUX_MIB_TCPACKCOMPRESSED),
        SNMP_MIB_ITEM("TCPZeroWindowDrop", LINUX_MIB_TCPZEROWINDOWDROP),
        SNMP_MIB_ITEM("TCPRcvQDrop", LINUX_MIB_TCPRCVQDROP),
+       SNMP_MIB_ITEM("TCPWqueueTooBig", LINUX_MIB_TCPWQUEUETOOBIG),
        SNMP_MIB_SENTINEL
 };
 

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index c8a29601a974cad4af806277cc6b170b70e1586d..576379f0e6ada5eba2090a40f926e5a8d3308e49 100644 (file)
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1299,6 +1299,11 @@ int tcp_fragment(struct sock *sk, enum tcp_queue tcp_queue,
        if (nsize < 0)
                nsize = 0;
 
+       if (unlikely((sk->sk_wmem_queued >> 1) > sk->sk_sndbuf)) {
+               NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPWQUEUETOOBIG);
+               return -ENOMEM;
+       }
+
        if (skb_unclone(skb, gfp))
                return -ENOMEM;