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

[musl] / src / network / lookup_name.c

diff --git a/src/network/lookup_name.c b/src/network/lookup_name.c
index 37d481f..f268bcd 100644 (file)
--- a/src/network/lookup_name.c
+++ b/src/network/lookup_name.c
@@ -102,45 +102,50 @@ struct dpc_ctx {
        struct address *addrs;
        char *canon;
        int cnt;
+       int rrtype;
 };
 
 #define RR_A 1
 #define RR_CNAME 5
 #define RR_AAAA 28
 
-static int dns_parse_callback(void *c, int rr, const void *data, int len, const void *packet)
+#define ABUF_SIZE 768
+
+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 (ctx->cnt >= MAXADDRS) return -1;
+       if (rr == RR_CNAME) {
+               if (__dn_expand(packet, (const unsigned char *)packet + plen,
+                   data, tmp, sizeof tmp) > 0 && is_valid_hostname(tmp))
+                       strcpy(ctx->canon, tmp);
+               return 0;
+       }
+       if (ctx->cnt >= MAXADDRS) return 0;
+       if (rr != ctx->rrtype) return 0;
        switch (rr) {
        case RR_A:
                if (len != 4) return -1;
-               ctx->addrs[ctx->cnt].family = AF_INET;
-               ctx->addrs[ctx->cnt].scopeid = 0;
-               memcpy(ctx->addrs[ctx->cnt++].addr, data, 4);
+               family = AF_INET;
                break;
        case RR_AAAA:
                if (len != 16) return -1;
-               ctx->addrs[ctx->cnt].family = AF_INET6;
-               ctx->addrs[ctx->cnt].scopeid = 0;
-               memcpy(ctx->addrs[ctx->cnt++].addr, data, 16);
-               break;
-       case RR_CNAME:
-               if (__dn_expand(packet, (const unsigned char *)packet + 512,
-                   data, tmp, sizeof tmp) > 0 && is_valid_hostname(tmp))
-                       strcpy(ctx->canon, tmp);
+               family = AF_INET6;
                break;
        }
+       ctx->addrs[ctx->cnt].family = family;
+       ctx->addrs[ctx->cnt].scopeid = 0;
+       memcpy(ctx->addrs[ctx->cnt++].addr, data, len);
        return 0;
 }
 
 static int name_from_dns(struct address buf[static MAXADDRS], char canon[static 256], const char *name, int family, const struct resolvconf *conf)
 {
-       unsigned char qbuf[2][280], abuf[2][512];
+       unsigned char qbuf[2][280], abuf[2][ABUF_SIZE];
        const unsigned char *qp[2] = { qbuf[0], qbuf[1] };
        unsigned char *ap[2] = { abuf[0], abuf[1] };
-       int qlens[2], alens[2];
+       int qlens[2], alens[2], qtypes[2];
        int i, nq = 0;
        struct dpc_ctx ctx = { .addrs = buf, .canon = canon };
        static const struct { int af; int rr; } afrr[2] = {
@@ -154,6 +159,7 @@ static int name_from_dns(struct address buf[static MAXADDRS], char canon[static
                                0, 0, 0, qbuf[nq], sizeof *qbuf);
                        if (qlens[nq] == -1)
                                return 0;
+                       qtypes[nq] = afrr[i].rr;
                        qbuf[nq][3] = 0; /* don't need AD flag */
                        /* Ensure query IDs are distinct. */
                        if (nq && qbuf[nq][0] == qbuf[0][0])
@@ -171,8 +177,10 @@ static int name_from_dns(struct address buf[static MAXADDRS], char canon[static
                if ((abuf[i][3] & 15) != 0) return EAI_FAIL;
        }
 
-       for (i=0; i<nq; i++)
+       for (i=nq-1; i>=0; i--) {
+               ctx.rrtype = qtypes[i];
                __dns_parse(abuf[i], alens[i], dns_parse_callback, &ctx);
+       }
 
        if (ctx.cnt) return ctx.cnt;
        return EAI_NODATA;