ASUS DSL-AC3100 Router Firmware radvd Bugs

Lets look at packet processing in the router code

                case ND_OPT_RDNSS_INFORMATION:
                        rdnssinfo = (struct nd_opt_rdnss_info_local *) opt_str;
                        count = rdnssinfo->nd_opt_rdnssi_len;

                         /* Check the RNDSS addresses received */
                        switch (count) {
                                case 7:

Now opt_str is the options part of the packet. Does the code check that the packet is big enough to account for these options? No. There are a bunch of cases like this. All lead to out of bounds memory access.

Lets look at the current radvd source from a recent Linux distro

                case ND_OPT_RDNSS_INFORMATION: {
                        char rdnss_str[INET6_ADDRSTRLEN];
                        struct AdvRDNSS *rdnss = 0;
                        struct nd_opt_rdnss_info_local *rdnssinfo = (struct nd_opt_rdnss_info_local *)opt_str;
                        if (len < sizeof(*rdnssinfo))
                                return;
                        int count = rdnssinfo->nd_opt_rdnssi_len;

                        /* Check the RNDSS addresses received */
                        switch (count) {
                        case 7:

It's clearly been fixed. But the patches haven't been backported to the router firmware.

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