tcp: CVE-2019-11478

tcp: tcp_fragment() should apply sane memory limits
tcp: refine memory limit test in tcp_fragment()

References:
https://nvd.nist.gov/vuln/detail/CVE-2019-11478
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=linux-4.9.y&id=e358f4af19db46ca25cc9a8a78412b09ba98859d
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=linux-4.9.y&id=caa51edc7e9606418611e68de624efbd0042adf5

Change-Id: Ie16affeda488857ce013ce3be578c05619aee446
Signed-off-by: Andreas Wellving <andreas.wellving@enea.com>

1 files changed, 86 insertions, 0 deletions

diff --git a/patches/cve/CVE-2019-11478-tcp-tcp_fragment-should-apply-sane-memory-limits.patch b/patches/cve/CVE-2019-11478-tcp-tcp_fragment-should-apply-sane-memory-limits.patch
new file mode 100644
index 0000000..7d0c4f4
--- /dev/null
+++ b/patches/cve/CVE-2019-11478-tcp-tcp_fragment-should-apply-sane-memory-limits.patch
@@ -0,0 +1,86 @@
+From e358f4af19db46ca25cc9a8a78412b09ba98859d Mon Sep 17 00:00:00 2001
+From: Eric Dumazet <edumazet@google.com>
+Date: Sat, 15 Jun 2019 17:40:56 -0700
+Subject: [PATCH] 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
+
+CVE: CVE-2019-11478
+Upstream-Status: Backport [https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=linux-4.9.y&id=e358f4af19db46ca25cc9a8a78412b09ba98859d]
+
+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>
+Signed-off-by: Andreas Wellving <andreas.wellving@enea.com>
+---
+ include/uapi/linux/snmp.h | 1 +
+ net/ipv4/proc.c           | 1 +
+ net/ipv4/tcp_output.c     | 5 +++++
+ 3 files changed, 7 insertions(+)
+
+diff --git a/include/uapi/linux/snmp.h b/include/uapi/linux/snmp.h
+index 3442a26d36d9..56e3460d1f9f 100644
+--- a/include/uapi/linux/snmp.h
++++ b/include/uapi/linux/snmp.h
+@@ -282,6 +282,7 @@ enum
+        LINUX_MIB_TCPKEEPALIVE,                 /* TCPKeepAlive */
+        LINUX_MIB_TCPMTUPFAIL,                  /* TCPMTUPFail */
+        LINUX_MIB_TCPMTUPSUCCESS,               /* TCPMTUPSuccess */
++       LINUX_MIB_TCPWQUEUETOOBIG,              /* TCPWqueueTooBig */
+        __LINUX_MIB_MAX
+ };
+ 
+diff --git a/net/ipv4/proc.c b/net/ipv4/proc.c
+index ec48d8eafc7e..8b221398534b 100644
+--- a/net/ipv4/proc.c
++++ b/net/ipv4/proc.c
+@@ -306,6 +306,7 @@ static const struct snmp_mib snmp4_net_list[] = {
+        SNMP_MIB_ITEM("TCPKeepAlive", LINUX_MIB_TCPKEEPALIVE),
+        SNMP_MIB_ITEM("TCPMTUPFail", LINUX_MIB_TCPMTUPFAIL),
+        SNMP_MIB_ITEM("TCPMTUPSuccess", LINUX_MIB_TCPMTUPSUCCESS),
++       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 2f166662682e..123b2d8fde46 100644
+--- a/net/ipv4/tcp_output.c
++++ b/net/ipv4/tcp_output.c
+@@ -1185,6 +1185,11 @@ int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len,
+        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;
+ 
+-- 
+2.20.1
+