From 024bc211772338002f964b1f6dd223e638428665 Mon Sep 17 00:00:00 2001 From: Roy Marples Date: Fri, 3 May 2019 14:44:06 +0100 Subject: [PATCH] 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 for finding this. --- src/dhcp6.c | 44 +++++++++++++++++++++----------------------- 1 file 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 + -- 2.47.2