hostnames.c: fix scan-build warning

This is breaking scan-build in CI[1]:

    /usr/share/clang/scan-build-14/bin/../libexec/ccc-analyzer [...] -c hostnames.c -o hostnames.o
    hostnames.c:59:10: warning: Null pointer passed to 1st parameter expecting 'nonnull' [core.NonNullParamChecker]
                    return strdup(rv);
                           ^~~~~~~~~~
    1 warning generated.

Likely caused by commit d2802ce60 ("fnettrace cleanup", 2023-07-15).

This also fixes a memory leak of `cmd`.

[1] https://github.com/netblue30/firejail/actions/runs/5568460702/jobs/10171098449

1 files changed, 21 insertions, 19 deletions

diff --git a/src/fnettrace/hostnames.c b/src/fnettrace/hostnames.c
index 7cb34e2c4..14ebc4ca0 100644
--- a/src/fnettrace/hostnames.c
+++ b/src/fnettrace/hostnames.c
@@ -40,30 +40,32 @@ char *retrieve_hostname(uint32_t ip) {
                 errExit("asprintf");
 
         FILE *fp = popen(cmd, "r");
-        if (fp) {
-                char *ptr;
-                 if (fgets(buf, MAXBUF, fp)) {
-                        ptr = strchr(buf, '\n');
-                        if (ptr)
-                                *ptr = '\0';
-                        if (strncmp(buf, "GeoIP Country Edition:", 22) == 0) {
-                                ptr = buf + 22;
-                                if (*ptr == ' ' && *(ptr + 3) == ',' &&  *(ptr + 4) == ' ') {
-                                        rv = ptr + 5;
-                                        if (strcmp(rv, "United States") == 0)
-                                                rv = "US";
-                                }
+        if (!fp) {
+                geoip_not_found = 1;
+                goto out;
+        }
+
+        char *ptr;
+        if (fgets(buf, MAXBUF, fp)) {
+                ptr = strchr(buf, '\n');
+                if (ptr)
+                        *ptr = '\0';
+                if (strncmp(buf, "GeoIP Country Edition:", 22) == 0) {
+                        ptr = buf + 22;
+                        if (*ptr == ' ' && *(ptr + 3) == ',' && *(ptr + 4) == ' ') {
+                                rv = ptr + 5;
+                                if (strcmp(rv, "United States") == 0)
+                                        rv = "US";
                         }
                 }
-                pclose(fp);
-                return strdup(rv);
         }
-        else
-                geoip_not_found = 1;
+        pclose(fp);
+        if (rv)
+                rv = strdup(rv);
 
+out:
         free(cmd);
-
-        return NULL;
+        return rv;
 }
 
 void load_hostnames(const char *fname) {