A6: return FORMERR in fromwire if bits are non zero.

oss_fuzz: Issue 24864: bind9:dns_rdata_fromwire_text_fuzzer: Overwrites-const-input in dns_rdata_fromwire_text_fuzzer

diff --git a/lib/dns/rdata/in_1/a6_38.c b/lib/dns/rdata/in_1/a6_38.c
index ac721aad4cb1db9384a61b2ffa68cdff50815c0d..d69c5d3dc2c898bc5858839e7af5cf71de3ba5c3 100644 (file)
--- a/lib/dns/rdata/in_1/a6_38.c
+++ b/lib/dns/rdata/in_1/a6_38.c
@@ -182,7 +182,9 @@ fromwire_in_a6(ARGS_FROMWIRE) {
                        return (ISC_R_UNEXPECTEDEND);
                }
                mask = 0xff >> (prefixlen % 8);
-               sr.base[0] &= mask; /* Ensure pad bits are zero. */
+               if ((sr.base[0] & ~mask) != 0) {
+                       return (DNS_R_FORMERR);
+               }
                RETERR(mem_tobuffer(target, sr.base, octets));
                isc_buffer_forward(source, octets);
        }