slirp: check pkt_len before reading protocol header

While processing ARP/NCSI packets in 'arp_input' or 'ncsi_input'
routines, ensure that pkt_len is large enough to accommodate the
respective protocol headers, lest it should do an OOB access.
Add check to avoid it.

CVE-2020-29129 CVE-2020-29130
  QEMU: slirp: out-of-bounds access while processing ARP/NCSI packets
 -> https://www.openwall.com/lists/oss-security/2020/11/27/1

Reported-by: Qiuhao Li <Qiuhao.Li@outlook.com>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
Message-Id: <20201126135706.273950-1-ppandit@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
(cherry-picked from 2e1dcbc0)
Signed-off-by: Alex Chen <alex.chen@huawei.com>

qemu.spec

@@ -1,6 +1,6 @@
 Name: qemu
 Version: 4.1.0
-Release: 34
+Release: 35
 Epoch: 2
 Summary: QEMU is a generic and open source machine emulator and virtualizer
 License: GPLv2 and BSD and MIT and CC-BY
@@ -280,6 +280,7 @@ Patch0267: multifd-tls-fix-memoryleak-of-the-QIOChannelSocket-o.patch
 Patch0268: net-remove-an-assert-call-in-eth_get_gso_type.patch
 Patch0269: json-Fix-a-memleak-in-parse_pair.patch
 Patch0270: Bugfix-hw-acpi-Use-max_cpus-instead-of-cpus-when-bui.patch
+Patch0271: slirp-check-pkt_len-before-reading-protocol-header.patch
 
 BuildRequires: flex
 BuildRequires: bison
@@ -626,6 +627,9 @@ getent passwd qemu >/dev/null || \
 %endif
 
 %changelog
+* Fri Dec 11 2020 Huawei Technologies Co., Ltd <alex.chen@huawei.com>
+- slirp: check pkt_len before reading protocol header for fixing CVE-2020-29129 and CVE-2020-29130
+
 * Thu Oct 29 2020 Huawei Technologies Co., Ltd <alex.chen@huawei.com>
 - Bugfix: hw/acpi: Use max_cpus instead of cpus when build PPTT table
 

slirp-check-pkt_len-before-reading-protocol-header.patch

@@ -0,0 +1,61 @@
+From c2df0d478b2605da10363ab57825cdbc34caa680 Mon Sep 17 00:00:00 2001
+From: Alex Chen <alex.chen@huawei.com>
+Date: Mon, 14 Dec 2020 15:39:46 +0800
+Subject: [PATCH] slirp: check pkt_len before reading protocol header
+MIME-Version: 1.0
+Content-Type: text/plain; charset=UTF-8
+Content-Transfer-Encoding: 8bit
+
+While processing ARP/NCSI packets in 'arp_input' or 'ncsi_input'
+routines, ensure that pkt_len is large enough to accommodate the
+respective protocol headers, lest it should do an OOB access.
+Add check to avoid it.
+
+CVE-2020-29129 CVE-2020-29130
+  QEMU: slirp: out-of-bounds access while processing ARP/NCSI packets
+ -> https://www.openwall.com/lists/oss-security/2020/11/27/1
+
+Reported-by: Qiuhao Li <Qiuhao.Li@outlook.com>
+Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
+Message-Id: <20201126135706.273950-1-ppandit@redhat.com>
+Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
+(cherry-picked from 2e1dcbc0)
+Signed-off-by: Alex Chen <alex.chen@huawei.com>
+---
+ slirp/src/ncsi.c  | 4 ++++
+ slirp/src/slirp.c | 4 ++++
+ 2 files changed, 8 insertions(+)
+
+diff --git a/slirp/src/ncsi.c b/slirp/src/ncsi.c
+index 6864b735..251c0d2b 100644
+--- a/slirp/src/ncsi.c
++++ b/slirp/src/ncsi.c
+@@ -147,6 +147,10 @@ void ncsi_input(Slirp *slirp, const uint8_t *pkt, int pkt_len)
+     uint32_t checksum;
+     uint32_t *pchecksum;
+ 
++    if (pkt_len < ETH_HLEN + sizeof(struct ncsi_pkt_hdr)) {
++        return; /* packet too short */
++    }
++
+     memset(ncsi_reply, 0, sizeof(ncsi_reply));
+ 
+     memset(reh->h_dest, 0xff, ETH_ALEN);
+diff --git a/slirp/src/slirp.c b/slirp/src/slirp.c
+index b0194cb3..86b0f52d 100644
+--- a/slirp/src/slirp.c
++++ b/slirp/src/slirp.c
+@@ -700,6 +700,10 @@ static void arp_input(Slirp *slirp, const uint8_t *pkt, int pkt_len)
+         return;
+     }
+ 
++    if (pkt_len < ETH_HLEN + sizeof(struct slirp_arphdr)) {
++        return; /* packet too short */
++    }
++
+     ar_op = ntohs(ah->ar_op);
+     switch (ar_op) {
+     case ARPOP_REQUEST:
+-- 
+2.23.0
+