dnsmasq: Backport DHCPv6 server fix (CVE-2022-0934)

This backports a commit from upstream dnsmasq to fix CVE-2022-0934.

CVE-2022-0934 description:
A single-byte, non-arbitrary write/use-after-free flaw was found in
dnsmasq. This flaw allows an attacker who sends a crafted packet
processed by dnsmasq, potentially causing a denial of service.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>

diff --git a/package/network/services/dnsmasq/patches/001-CVE-2022-0934-Fix-write-after-free-error-in-DHCPv6-code.patch b/package/network/services/dnsmasq/patches/001-CVE-2022-0934-Fix-write-after-free-error-in-DHCPv6-code.patch
new file mode 100644 (file)
index 0000000..4113be9
--- /dev/null
+++ b/package/network/services/dnsmasq/patches/001-CVE-2022-0934-Fix-write-after-free-error-in-DHCPv6-code.patch
@@ -0,0 +1,179 @@
+From 03345ecefeb0d82e3c3a4c28f27c3554f0611b39 Mon Sep 17 00:00:00 2001
+From: Simon Kelley <simon@thekelleys.org.uk>
+Date: Thu, 31 Mar 2022 21:35:20 +0100
+Subject: Fix write-after-free error in DHCPv6 code. CVE-2022-0934 refers.
+
+---
+ CHANGELOG     |  3 +++
+ src/rfc3315.c | 48 +++++++++++++++++++++++++++---------------------
+ 2 files changed, 30 insertions(+), 21 deletions(-)
+
+--- a/CHANGELOG
++++ b/CHANGELOG
+@@ -92,6 +92,9 @@ version 2.86
+       of filename). Thanks to Ed Wildgoose for the initial patch
+       and motivation for this.
+ 
++      Fix write-after-free error in DHCPv6 server code.
++      CVE-2022-0934 refers.
++      
+       
+ version 2.85
+         Fix problem with DNS retries in 2.83/2.84.
+--- a/src/rfc3315.c
++++ b/src/rfc3315.c
+@@ -33,9 +33,9 @@ struct state {
+   unsigned int mac_len, mac_type;
+ };
+ 
+-static int dhcp6_maybe_relay(struct state *state, void *inbuff, size_t sz, 
++static int dhcp6_maybe_relay(struct state *state, unsigned char *inbuff, size_t sz, 
+                            struct in6_addr *client_addr, int is_unicast, time_t now);
+-static int dhcp6_no_relay(struct state *state, int msg_type, void *inbuff, size_t sz, int is_unicast, time_t now);
++static int dhcp6_no_relay(struct state *state, int msg_type, unsigned char *inbuff, size_t sz, int is_unicast, time_t now);
+ static void log6_opts(int nest, unsigned int xid, void *start_opts, void *end_opts);
+ static void log6_packet(struct state *state, char *type, struct in6_addr *addr, char *string);
+ static void log6_quiet(struct state *state, char *type, struct in6_addr *addr, char *string);
+@@ -104,12 +104,12 @@ unsigned short dhcp6_reply(struct dhcp_c
+ }
+ 
+ /* This cost me blood to write, it will probably cost you blood to understand - srk. */
+-static int dhcp6_maybe_relay(struct state *state, void *inbuff, size_t sz, 
++static int dhcp6_maybe_relay(struct state *state, unsigned char *inbuff, size_t sz, 
+                            struct in6_addr *client_addr, int is_unicast, time_t now)
+ {
+   void *end = inbuff + sz;
+   void *opts = inbuff + 34;
+-  int msg_type = *((unsigned char *)inbuff);
++  int msg_type = *inbuff;
+   unsigned char *outmsgtypep;
+   void *opt;
+   struct dhcp_vendor *vendor;
+@@ -259,15 +259,15 @@ static int dhcp6_maybe_relay(struct stat
+   return 1;
+ }
+ 
+-static int dhcp6_no_relay(struct state *state, int msg_type, void *inbuff, size_t sz, int is_unicast, time_t now)
++static int dhcp6_no_relay(struct state *state, int msg_type, unsigned char *inbuff, size_t sz, int is_unicast, time_t now)
+ {
+   void *opt;
+-  int i, o, o1, start_opts;
++  int i, o, o1, start_opts, start_msg;
+   struct dhcp_opt *opt_cfg;
+   struct dhcp_netid *tagif;
+   struct dhcp_config *config = NULL;
+   struct dhcp_netid known_id, iface_id, v6_id;
+-  unsigned char *outmsgtypep;
++  unsigned char outmsgtype;
+   struct dhcp_vendor *vendor;
+   struct dhcp_context *context_tmp;
+   struct dhcp_mac *mac_opt;
+@@ -296,12 +296,13 @@ static int dhcp6_no_relay(struct state *
+   v6_id.next = state->tags;
+   state->tags = &v6_id;
+ 
+-  /* copy over transaction-id, and save pointer to message type */
+-  if (!(outmsgtypep = put_opt6(inbuff, 4)))
++  start_msg = save_counter(-1);
++  /* copy over transaction-id */
++  if (!put_opt6(inbuff, 4))
+     return 0;
+   start_opts = save_counter(-1);
+-  state->xid = outmsgtypep[3] | outmsgtypep[2] << 8 | outmsgtypep[1] << 16;
+-   
++  state->xid = inbuff[3] | inbuff[2] << 8 | inbuff[1] << 16;
++    
+   /* We're going to be linking tags from all context we use. 
+      mark them as unused so we don't link one twice and break the list */
+   for (context_tmp = state->context; context_tmp; context_tmp = context_tmp->current)
+@@ -347,7 +348,7 @@ static int dhcp6_no_relay(struct state *
+       (msg_type == DHCP6REQUEST || msg_type == DHCP6RENEW || msg_type == DHCP6RELEASE || msg_type == DHCP6DECLINE))
+     
+     {  
+-      *outmsgtypep = DHCP6REPLY;
++      outmsgtype = DHCP6REPLY;
+       o1 = new_opt6(OPTION6_STATUS_CODE);
+       put_opt6_short(DHCP6USEMULTI);
+       put_opt6_string("Use multicast");
+@@ -619,11 +620,11 @@ static int dhcp6_no_relay(struct state *
+       struct dhcp_netid *solicit_tags;
+       struct dhcp_context *c;
+       
+-      *outmsgtypep = DHCP6ADVERTISE;
++      outmsgtype = DHCP6ADVERTISE;
+       
+       if (opt6_find(state->packet_options, state->end, OPTION6_RAPID_COMMIT, 0))
+         {
+-          *outmsgtypep = DHCP6REPLY;
++          outmsgtype = DHCP6REPLY;
+           state->lease_allocate = 1;
+           o = new_opt6(OPTION6_RAPID_COMMIT);
+           end_opt6(o);
+@@ -809,7 +810,7 @@ static int dhcp6_no_relay(struct state *
+       int start = save_counter(-1);
+ 
+       /* set reply message type */
+-      *outmsgtypep = DHCP6REPLY;
++      outmsgtype = DHCP6REPLY;
+       state->lease_allocate = 1;
+ 
+       log6_quiet(state, "DHCPREQUEST", NULL, ignore ? _("ignored") : NULL);
+@@ -924,7 +925,7 @@ static int dhcp6_no_relay(struct state *
+       int address_assigned = 0;
+ 
+       /* set reply message type */
+-      *outmsgtypep = DHCP6REPLY;
++      outmsgtype = DHCP6REPLY;
+       
+       log6_quiet(state, msg_type == DHCP6RENEW ? "DHCPRENEW" : "DHCPREBIND", NULL, NULL);
+ 
+@@ -1057,7 +1058,7 @@ static int dhcp6_no_relay(struct state *
+       int good_addr = 0;
+ 
+       /* set reply message type */
+-      *outmsgtypep = DHCP6REPLY;
++      outmsgtype = DHCP6REPLY;
+       
+       log6_quiet(state, "DHCPCONFIRM", NULL, NULL);
+       
+@@ -1121,7 +1122,7 @@ static int dhcp6_no_relay(struct state *
+       log6_quiet(state, "DHCPINFORMATION-REQUEST", NULL, ignore ? _("ignored") : state->hostname);
+       if (ignore)
+         return 0;
+-      *outmsgtypep = DHCP6REPLY;
++      outmsgtype = DHCP6REPLY;
+       tagif = add_options(state, 1);
+       break;
+       }
+@@ -1130,7 +1131,7 @@ static int dhcp6_no_relay(struct state *
+     case DHCP6RELEASE:
+       {
+       /* set reply message type */
+-      *outmsgtypep = DHCP6REPLY;
++      outmsgtype = DHCP6REPLY;
+ 
+       log6_quiet(state, "DHCPRELEASE", NULL, NULL);
+ 
+@@ -1195,7 +1196,7 @@ static int dhcp6_no_relay(struct state *
+     case DHCP6DECLINE:
+       {
+       /* set reply message type */
+-      *outmsgtypep = DHCP6REPLY;
++      outmsgtype = DHCP6REPLY;
+       
+       log6_quiet(state, "DHCPDECLINE", NULL, NULL);
+ 
+@@ -1275,7 +1276,12 @@ static int dhcp6_no_relay(struct state *
+       }
+ 
+     }
+-  
++
++  /* Fill in the message type. Note that we store the offset,
++     not a direct pointer, since the packet memory may have been 
++     reallocated. */
++  ((unsigned char *)(daemon->outpacket.iov_base))[start_msg] = outmsgtype;
++
+   log_tags(tagif, state->xid);
+   log6_opts(0, state->xid, daemon->outpacket.iov_base + start_opts, daemon->outpacket.iov_base + save_counter(-1));
+