prevent CNAME/PTR parsing from reading data past the response end

DNS parsing callbacks pass the response buffer end instead of the actual
response end to dn_expand, so a malformed DNS response can use message
compression to make dn_expand jump past the response end and attempt to
parse uninitialized parts of that buffer, which might succeed and return
garbage.

diff --git a/src/network/dns_parse.c b/src/network/dns_parse.c
index 320df60..7f83e79 100644 (file)
--- a/src/network/dns_parse.c
+++ b/src/network/dns_parse.c
@@ -1,7 +1,7 @@
 #include <string.h>
 #include "lookup.h"
 
-int __dns_parse(const unsigned char *r, int rlen, int (*callback)(void *, int, const void *, int, const void *), void *ctx)
+int __dns_parse(const unsigned char *r, int rlen, int (*callback)(void *, int, const void *, int, const void *, int), void *ctx)
 {
        int qdcount, ancount;
        const unsigned char *p;
@@ -26,7 +26,7 @@ int __dns_parse(const unsigned char *r, int rlen, int (*callback)(void *, int, c
                p += 1 + !!*p;
                len = p[8]*256 + p[9];
                if (len+10 > r+rlen-p) return -1;
-               if (callback(ctx, p[1], p+10, len, r) < 0) return -1;
+               if (callback(ctx, p[1], p+10, len, r, rlen) < 0) return -1;
                p += 10 + len;
        }
        return 0;

diff --git a/src/network/getnameinfo.c b/src/network/getnameinfo.c
index 949e181..080d3c0 100644 (file)
--- a/src/network/getnameinfo.c
+++ b/src/network/getnameinfo.c
@@ -108,10 +108,10 @@ static void reverse_services(char *buf, int port, int dgram)
        __fclose_ca(f);
 }
 
-static int dns_parse_callback(void *c, int rr, const void *data, int len, const void *packet)
+static int dns_parse_callback(void *c, int rr, const void *data, int len, const void *packet, int plen)
 {
        if (rr != RR_PTR) return 0;
-       if (__dn_expand(packet, (const unsigned char *)packet + 512,
+       if (__dn_expand(packet, (const unsigned char *)packet + plen,
            data, c, 256) <= 0)
                *(char *)c = 0;
        return 0;

diff --git a/src/network/lookup.h b/src/network/lookup.h
index ef66272..54b2f8b 100644 (file)
--- a/src/network/lookup.h
+++ b/src/network/lookup.h
@@ -50,6 +50,6 @@ hidden int __lookup_ipliteral(struct address buf[static 1], const char *name, in
 hidden int __get_resolv_conf(struct resolvconf *, char *, size_t);
 hidden int __res_msend_rc(int, const unsigned char *const *, const int *, unsigned char *const *, int *, int, const struct resolvconf *);
 
-hidden int __dns_parse(const unsigned char *, int, int (*)(void *, int, const void *, int, const void *), void *);
+hidden int __dns_parse(const unsigned char *, int, int (*)(void *, int, const void *, int, const void *, int), void *);
 
 #endif

diff --git a/src/network/lookup_name.c b/src/network/lookup_name.c
index 5f6867c..f268bcd 100644 (file)
--- a/src/network/lookup_name.c
+++ b/src/network/lookup_name.c
@@ -111,13 +111,13 @@ struct dpc_ctx {
 
 #define ABUF_SIZE 768
 
-static int dns_parse_callback(void *c, int rr, const void *data, int len, const void *packet)
+static int dns_parse_callback(void *c, int rr, const void *data, int len, const void *packet, int plen)
 {
        char tmp[256];
        int family;
        struct dpc_ctx *ctx = c;
        if (rr == RR_CNAME) {
-               if (__dn_expand(packet, (const unsigned char *)packet + ABUF_SIZE,
+               if (__dn_expand(packet, (const unsigned char *)packet + plen,
                    data, tmp, sizeof tmp) > 0 && is_valid_hostname(tmp))
                        strcpy(ctx->canon, tmp);
                return 0;