tools/xenstored: control: Store the save filename in lu_dump_state

The function lu_close_dump_state() will use talloc_asprintf() without
checking whether the allocation succeeded. In the unlikely case we are
out of memory, we would dereference a NULL pointer.

As we already computed the filename in lu_get_dump_state(), we can store
the name in the lu_dump_state. This is avoiding to deal with memory file
in the close path and also reduce the risk to use the different
filename.

This bug was discovered and resolved using Coverity Static Analysis
Security Testing (SAST) by Synopsys, Inc.

Fixes: c0dc6a3e7c ("tools/xenstore: read internal state when doing live upgrade")
Signed-off-by: Julien Grall <jgrall@amazon.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Release-Acked-by: Ian Jackson <iwj@xenproject.org>

tools/xenstore/xenstored_control.c

@@ -16,6 +16,7 @@ Interactive commands for Xen Store Daemon.
     along with this program; If not, see <http://www.gnu.org/licenses/>.
 */
 
+#include <assert.h>
 #include <ctype.h>
 #include <errno.h>
 #include <stdarg.h>
@@ -74,6 +75,7 @@ struct lu_dump_state {
 	unsigned int size;
 #ifndef __MINIOS__
 	int fd;
+	char *filename;
 #endif
 };
 
@@ -399,17 +401,16 @@ static void lu_dump_close(FILE *fp)
 
 static void lu_get_dump_state(struct lu_dump_state *state)
 {
-	char *filename;
 	struct stat statbuf;
 
 	state->size = 0;
 
-	filename = talloc_asprintf(NULL, "%s/state_dump", xs_daemon_rootdir());
-	if (!filename)
+	state->filename = talloc_asprintf(NULL, "%s/state_dump",
+					  xs_daemon_rootdir());
+	if (!state->filename)
 		barf("Allocation failure");
 
-	state->fd = open(filename, O_RDONLY);
-	talloc_free(filename);
+	state->fd = open(state->filename, O_RDONLY);
 	if (state->fd < 0)
 		return;
 	if (fstat(state->fd, &statbuf) != 0)
@@ -431,14 +432,13 @@ static void lu_get_dump_state(struct lu_dump_state *state)
 
 static void lu_close_dump_state(struct lu_dump_state *state)
 {
-	char *filename;
+	assert(state->filename != NULL);
 
 	munmap(state->buf, state->size);
 	close(state->fd);
 
-	filename = talloc_asprintf(NULL, "%s/state_dump", xs_daemon_rootdir());
-	unlink(filename);
-	talloc_free(filename);
+	unlink(state->filename);
+	talloc_free(state->filename);
 }
 
 static char *lu_exec(const void *ctx, int argc, char **argv)