Properly fix memory leak in _nss_dns_gethostbyname4_r with big DNS answer

Instead of trying to guess whether the second buffer needs to be freed
set a flag at the place it is allocated

1 files changed, 26 insertions, 19 deletions

diff --git a/resolv/res_query.c b/resolv/res_query.c
index 88230f4..88c8255 100644
--- a/resolv/res_query.c
+++ b/resolv/res_query.c
@@ -98,7 +98,7 @@ static int
 __libc_res_nquerydomain(res_state statp, const char *name, const char *domain,
 			int class, int type, u_char *answer, int anslen,
 			u_char **answerp, u_char **answerp2, int *nanswerp2,
-			int *resplen2);
+			int *resplen2, int *answerp2_malloced);
 
 /*
  * Formulate a normal query, send, and await answer.
@@ -119,7 +119,8 @@ __libc_res_nquery(res_state statp,
 		  u_char **answerp,	/* if buffer needs to be enlarged */
 		  u_char **answerp2,
 		  int *nanswerp2,
-		  int *resplen2)
+		  int *resplen2,
+		  int *answerp2_malloced)
 {
 	HEADER *hp = (HEADER *) answer;
 	HEADER *hp2;
@@ -224,7 +225,8 @@ __libc_res_nquery(res_state statp,
 	}
 	assert (answerp == NULL || (void *) *answerp == (void *) answer);
 	n = __libc_res_nsend(statp, query1, nquery1, query2, nquery2, answer,
-			     anslen, answerp, answerp2, nanswerp2, resplen2);
+			     anslen, answerp, answerp2, nanswerp2, resplen2,
+			     answerp2_malloced);
 	if (use_malloc)
 		free (buf);
 	if (n < 0) {
@@ -316,7 +318,7 @@ res_nquery(res_state statp,
 	   int anslen)		/* size of answer buffer */
 {
 	return __libc_res_nquery(statp, name, class, type, answer, anslen,
-				 NULL, NULL, NULL, NULL);
+				 NULL, NULL, NULL, NULL, NULL);
 }
 libresolv_hidden_def (res_nquery)
 
@@ -335,7 +337,8 @@ __libc_res_nsearch(res_state statp,
 		   u_char **answerp,
 		   u_char **answerp2,
 		   int *nanswerp2,
-		   int *resplen2)
+		   int *resplen2,
+		   int *answerp2_malloced)
 {
 	const char *cp, * const *domain;
 	HEADER *hp = (HEADER *) answer;
@@ -360,7 +363,7 @@ __libc_res_nsearch(res_state statp,
 	if (!dots && (cp = res_hostalias(statp, name, tmp, sizeof tmp))!= NULL)
 		return (__libc_res_nquery(statp, cp, class, type, answer,
 					  anslen, answerp, answerp2,
-					  nanswerp2, resplen2));
+					  nanswerp2, resplen2, answerp2_malloced));
 
 #ifdef DEBUG
 	if (statp->options & RES_DEBUG)
@@ -377,7 +380,8 @@ __libc_res_nsearch(res_state statp,
 	if (dots >= statp->ndots || trailing_dot) {
 		ret = __libc_res_nquerydomain(statp, name, NULL, class, type,
 					      answer, anslen, answerp,
-					      answerp2, nanswerp2, resplen2);
+					      answerp2, nanswerp2, resplen2,
+					      answerp2_malloced);
 		if (ret > 0 || trailing_dot)
 			return (ret);
 		saved_herrno = h_errno;
@@ -386,11 +390,11 @@ __libc_res_nsearch(res_state statp,
 			answer = *answerp;
 			anslen = MAXPACKET;
 		}
-		if (answerp2
-		    && (*answerp2 < answer || *answerp2 >= answer + anslen))
+		if (answerp2 && *answerp2_malloced)
 		  {
 		    free (*answerp2);
 		    *answerp2 = NULL;
+		    *answerp2_malloced = 0;
 		  }
 	}
 
@@ -417,7 +421,7 @@ __libc_res_nsearch(res_state statp,
 						      class, type,
 						      answer, anslen, answerp,
 						      answerp2, nanswerp2,
-						      resplen2);
+						      resplen2, answerp2_malloced);
 			if (ret > 0)
 				return (ret);
 
@@ -425,12 +429,11 @@ __libc_res_nsearch(res_state statp,
 				answer = *answerp;
 				anslen = MAXPACKET;
 			}
-			if (answerp2
-			    && (*answerp2 < answer
-				|| *answerp2 >= answer + anslen))
+			if (answerp2 && *answerp2_malloced)
 			  {
 			    free (*answerp2);
 			    *answerp2 = NULL;
+			    *answerp2_malloced = 0;
 			  }
 
 			/*
@@ -486,7 +489,8 @@ __libc_res_nsearch(res_state statp,
 	    && !(tried_as_is || root_on_list)) {
 		ret = __libc_res_nquerydomain(statp, name, NULL, class, type,
 					      answer, anslen, answerp,
-					      answerp2, nanswerp2, resplen2);
+					      answerp2, nanswerp2, resplen2,
+					      answerp2_malloced);
 		if (ret > 0)
 			return (ret);
 	}
@@ -498,10 +502,11 @@ __libc_res_nsearch(res_state statp,
 	 * else send back meaningless H_ERRNO, that being the one from
 	 * the last DNSRCH we did.
 	 */
-	if (answerp2 && (*answerp2 < answer || *answerp2 >= answer + anslen))
+	if (answerp2 && *answerp2_malloced)
 	  {
 	    free (*answerp2);
 	    *answerp2 = NULL;
+	    *answerp2_malloced = 0;
 	  }
 	if (saved_herrno != -1)
 		RES_SET_H_ERRNO(statp, saved_herrno);
@@ -521,7 +526,7 @@ res_nsearch(res_state statp,
 	    int anslen)		/* size of answer */
 {
 	return __libc_res_nsearch(statp, name, class, type, answer,
-				  anslen, NULL, NULL, NULL, NULL);
+				  anslen, NULL, NULL, NULL, NULL, NULL);
 }
 libresolv_hidden_def (res_nsearch)
 
@@ -539,7 +544,8 @@ __libc_res_nquerydomain(res_state statp,
 			u_char **answerp,
 			u_char **answerp2,
 			int *nanswerp2,
-			int *resplen2)
+			int *resplen2,
+			int *answerp2_malloced)
 {
 	char nbuf[MAXDNAME];
 	const char *longname = nbuf;
@@ -581,7 +587,7 @@ __libc_res_nquerydomain(res_state statp,
 	}
 	return (__libc_res_nquery(statp, longname, class, type, answer,
 				  anslen, answerp, answerp2, nanswerp2,
-				  resplen2));
+				  resplen2, answerp2_malloced));
 }
 
 int
@@ -593,7 +599,8 @@ res_nquerydomain(res_state statp,
 	    int anslen)		/* size of answer */
 {
 	return __libc_res_nquerydomain(statp, name, domain, class, type,
-				       answer, anslen, NULL, NULL, NULL, NULL);
+				       answer, anslen, NULL, NULL, NULL, NULL,
+				       NULL);
 }
 libresolv_hidden_def (res_nquerydomain)