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Solves CVE-2015-8605 that caused DoS when an invalid length field in IPv4 UDP
was received by the server.
Upstream-Status: Backport (v4.3.3p1)
CVE: CVE-2015-8605
From: https://source.isc.org/cgi-bin/gitweb.cgi?p=dhcp.git;a=commit;h=4ce21cb6301d665de01c1a6209e40f5f35072c0c
Signed-off-by: Mariano Lopez <mariano.lopez@linux.intel.com>
=======================================================================
diff --git a/common/packet.c b/common/packet.c
index b530432..e600e37 100644
--- a/common/packet.c
+++ b/common/packet.c
@@ -220,7 +220,28 @@ ssize_t decode_hw_header (interface, buf, bufix, from)
}
}
-/* UDP header and IP header decoded together for convenience. */
+/*!
+ *
+ * \brief UDP header and IP header decoded together for convenience.
+ *
+ * Attempt to decode the UDP and IP headers and, if necessary, checksum
+ * the packet.
+ *
+ * \param inteface - the interface on which the packet was recevied
+ * \param buf - a pointer to the buffer for the received packet
+ * \param bufix - where to start processing the buffer, previous
+ * routines may have processed parts of the buffer already
+ * \param from - space to return the address of the packet sender
+ * \param buflen - remaining length of the buffer, this will have been
+ * decremented by bufix by the caller
+ * \param rbuflen - space to return the length of the payload from the udp
+ * header
+ * \param csum_ready - indication if the checksum is valid for use
+ * non-zero indicates the checksum should be validated
+ *
+ * \return - the index to the first byte of the udp payload (that is the
+ * start of the DHCP packet
+ */
ssize_t
decode_udp_ip_header(struct interface_info *interface,
@@ -231,7 +252,7 @@ decode_udp_ip_header(struct interface_info *interface,
unsigned char *data;
struct ip ip;
struct udphdr udp;
- unsigned char *upp, *endbuf;
+ unsigned char *upp;
u_int32_t ip_len, ulen, pkt_len;
static unsigned int ip_packets_seen = 0;
static unsigned int ip_packets_bad_checksum = 0;
@@ -241,11 +262,8 @@ decode_udp_ip_header(struct interface_info *interface,
static unsigned int udp_packets_length_overflow = 0;
unsigned len;
- /* Designate the end of the input buffer for bounds checks. */
- endbuf = buf + bufix + buflen;
-
/* Assure there is at least an IP header there. */
- if ((buf + bufix + sizeof(ip)) > endbuf)
+ if (sizeof(ip) > buflen)
return -1;
/* Copy the IP header into a stack aligned structure for inspection.
@@ -257,13 +275,17 @@ decode_udp_ip_header(struct interface_info *interface,
ip_len = (*upp & 0x0f) << 2;
upp += ip_len;
- /* Check the IP packet length. */
+ /* Check packet lengths are within the buffer:
+ * first the ip header (ip_len)
+ * then the packet length from the ip header (pkt_len)
+ * then the udp header (ip_len + sizeof(udp)
+ * We are liberal in what we accept, the udp payload should fit within
+ * pkt_len, but we only check against the full buffer size.
+ */
pkt_len = ntohs(ip.ip_len);
- if (pkt_len > buflen)
- return -1;
-
- /* Assure after ip_len bytes that there is enough room for a UDP header. */
- if ((upp + sizeof(udp)) > endbuf)
+ if ((ip_len > buflen) ||
+ (pkt_len > buflen) ||
+ ((ip_len + sizeof(udp)) > buflen))
return -1;
/* Copy the UDP header into a stack aligned structure for inspection. */
@@ -284,7 +306,8 @@ decode_udp_ip_header(struct interface_info *interface,
return -1;
udp_packets_length_checked++;
- if ((upp + ulen) > endbuf) {
+ /* verify that the payload length from the udp packet fits in the buffer */
+ if ((ip_len + ulen) > buflen) {
udp_packets_length_overflow++;
if (((udp_packets_length_checked > 4) &&
(udp_packets_length_overflow != 0)) &&
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