Fix possible invalid memory references

Make sure strings are NULL terminated.
Prolems reported by Coverity

src/plugins/mpi/pmi2/info.c

@@ -84,7 +84,7 @@ enqueue_nag_req(int fd, int rank, char *key)
 	req = xmalloc(sizeof(nag_req_t));
 	req->fd = fd;
 	req->rank = rank;
-	strncpy(req->key, key, PMI2_MAX_KEYLEN);
+	strncpy(req->key, key, (PMI2_MAX_KEYLEN - 1));	/* Insure NULL at end */
 
 	/* insert in the head */
 	req->next = nag_req_list;

src/plugins/proctrack/linuxproc/kill_tree.c

@@ -332,7 +332,7 @@ extern pid_t find_ancestor(pid_t process, char *process_name)
 	int fd;
 	long pid, ppid;
 
-	rbuf = xmalloc(4096);
+	rbuf = xmalloc_nz(4096);
 	pid = ppid = (long)process;
 	do {
 		if (ppid <= 1) {
@@ -345,6 +345,7 @@ extern pid_t find_ancestor(pid_t process, char *process_name)
 			pid = 0;
 			break;
 		}
+		memset(rbuf, 0, 4096);
 		buf_used = read(fd, rbuf, 4096);
 		if ((buf_used <= 0) || (buf_used >= 4096)) {
 			close(fd);

src/plugins/task/affinity/cpuset.c

@@ -230,12 +230,12 @@ int	slurm_set_cpuset(char *base, char *path, pid_t pid, size_t size,
 	 * "mems" must be set before any tasks can be added. */
 	snprintf(file_path, sizeof(file_path), "%s/%smems",
 		 base, cpuset_prefix);
-	memset(mstr, 0, sizeof(mstr));
 	fd = open(file_path, O_RDONLY);
 	if (fd < 0) {
 		error("open(%s): %m", file_path);
 	} else {
-		rc = read(fd, mstr, sizeof(mstr));
+		memset(mstr, 0, sizeof(mstr));
+		rc = read(fd, mstr, sizeof(mstr)-1);	/* Insure NULL at end */
 		close(fd);
 		if (rc < 1) {
 			error("read(%s): %m", file_path);
@@ -306,7 +306,8 @@ int	slurm_get_cpuset(char *path, pid_t pid, size_t size, cpu_set_t *mask)
 		error("open(%s): %m", file_path);
 		return SLURM_ERROR;
 	}
-	rc = read(fd, mstr, sizeof(mstr));
+	memset(mstr, 0, sizeof(mstr));
+	rc = read(fd, mstr, sizeof(mstr)-1);	/* Insure NULL at end */
 	close(fd);
 	if (rc < 1) {
 		error("read(%s): %m", file_path);