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authorRoy Marples <roy@marples.name>2019-05-03 14:44:06 +0100
committerRoy Marples <roy@marples.name>2019-05-03 14:44:06 +0100
commitc1ebeaafeb324bac997984abdcee2d4e8b61a8a8 (patch)
tree3ccfe3b6f263bc02bd96435792a5b03dd70ce891
parent7b04db370b9efe5e532d3d81e366899b30f7c496 (diff)
DHCPv6: Fix a potential read overflow with D6_OPTION_PD_EXCLUDE
dhcpcd only checks that the prefix length of the exclusion matches the prefix length of the ia and equals the length of the data in the option. This could potentially overrun the in6_addr structure. This is fixed by enforcing RFC 6603 section 4.2 option limits more clearly. Thanks to Maxime Villard <max@m00nbsd.net> for finding this.
-rw-r--r--src/dhcp6.c44
1 files changed, 21 insertions, 23 deletions
diff --git a/src/dhcp6.c b/src/dhcp6.c
index dee8d4b6..583f3b3f 100644
--- a/src/dhcp6.c
+++ b/src/dhcp6.c
@@ -2166,40 +2166,38 @@ dhcp6_findpd(struct interface *ifp, const uint8_t *iaid,
state->expire = a->prefix_vltime;
i++;
- o = dhcp6_findoption(o, ol, D6_OPTION_PD_EXCLUDE, &ol);
a->prefix_exclude_len = 0;
memset(&a->prefix_exclude, 0, sizeof(a->prefix_exclude));
-#if 0
- if (ex == NULL) {
- struct dhcp6_option *w;
- uint8_t *wp;
-
- w = calloc(1, 128);
- w->len = htons(2);
- wp = D6_OPTION_DATA(w);
- *wp++ = 64;
- *wp++ = 0x78;
- ex = w;
- }
-#endif
+ o = dhcp6_findoption(o, ol, D6_OPTION_PD_EXCLUDE, &ol);
if (o == NULL)
continue;
- if (ol < 2) {
- logerrx("%s: truncated PD Exclude", ifp->name);
+
+ /* RFC 6603 4.2 says option length MUST be between 2 and 17.
+ * This allows 1 octet for prefix length and 16 for the
+ * subnet ID. */
+ if (ol < 2 || ol > 17) {
+ logerrx("%s: invalid PD Exclude option", ifp->name);
continue;
}
- a->prefix_exclude_len = *o++;
- ol--;
- if (((a->prefix_exclude_len - a->prefix_len - 1) / NBBY) + 1
- != ol)
- {
+
+ /* RFC 6603 4.2 says prefix length MUST be between the
+ * length of the IAPREFIX prefix length + 1 and 128. */
+ if (*o < a->prefix_len + 1 || *o > 128) {
+ logerrx("%s: invalid PD Exclude length", ifp->name);
+ continue;
+ }
+
+ /* Check option length matches prefix length. */
+ if (((*o - a->prefix_len - 1) / NBBY) + 1 != ol) {
logerrx("%s: PD Exclude length mismatch", ifp->name);
- a->prefix_exclude_len = 0;
continue;
}
- nb = a->prefix_len % NBBY;
+
+ a->prefix_exclude_len = *o++;
+ ol--;
memcpy(&a->prefix_exclude, &a->prefix,
sizeof(a->prefix_exclude));
+ nb = a->prefix_len % NBBY;
if (nb)
ol--;
pw = a->prefix_exclude.s6_addr +