virCommandExec: Report error if execve fails

In an unlikely event of execve() failing, the virCommandExec()
function does not report any error, even though checks that are
at the beginning of the function are verbose when failing.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

src/util/vircommand.c

@@ -2152,7 +2152,12 @@ int virCommandExec(virCommandPtr cmd)
         return -1;
     }
 
-    return execve(cmd->args[0], cmd->args, cmd->env);
+    execve(cmd->args[0], cmd->args, cmd->env);
+
+    virReportSystemError(errno,
+                         _("cannot execute binary %s"),
+                         cmd->args[0]);
+    return -1;
 }
 #else
 int virCommandExec(virCommandPtr cmd ATTRIBUTE_UNUSED)

tests/commandtest.c

@@ -1063,6 +1063,74 @@ static int test24(const void *unused ATTRIBUTE_UNUSED)
     return ret;
 }
 
+
+static int test25(const void *unused ATTRIBUTE_UNUSED)
+{
+    int ret = -1;
+    int pipeFD[2] = { -1, -1};
+    char rv = 0;
+    ssize_t tries = 100;
+    pid_t pid;
+
+    if (pipe(pipeFD) < 0) {
+        fprintf(stderr, "Unable to create pipe\n");
+        goto cleanup;
+    }
+
+    if (virSetNonBlock(pipeFD[0]) < 0) {
+        fprintf(stderr, "Unable to make read end of pipe nonblocking\n");
+        goto cleanup;
+    }
+
+    /* Now, fork and try to exec a nonexistent binary. */
+    pid = virFork();
+    if (pid < 0) {
+        fprintf(stderr, "Unable to spawn child\n");
+        goto cleanup;
+    }
+
+    if (pid == 0) {
+        /* Child */
+        virCommandPtr cmd = virCommandNew("some/nonexistent/binary");
+
+        rv = virCommandExec(cmd);
+        if (safewrite(pipeFD[1], &rv, sizeof(rv)) < 0)
+            fprintf(stderr, "Unable to write to pipe\n");
+        _exit(EXIT_FAILURE);
+    }
+
+    /* Parent */
+    while (--tries) {
+        if (saferead(pipeFD[0], &rv, sizeof(rv)) < 0) {
+            if (errno != EWOULDBLOCK) {
+                fprintf(stderr, "Unable to read from pipe\n");
+                goto cleanup;
+            }
+
+            usleep(10 * 1000);
+        } else {
+            break;
+        }
+    }
+
+    if (!tries) {
+        fprintf(stderr, "Child hasn't returned anything\n");
+        goto cleanup;
+    }
+
+    if (rv >= 0) {
+        fprintf(stderr, "Child should have returned an error\n");
+        goto cleanup;
+    }
+
+    ret = 0;
+ cleanup:
+    VIR_FORCE_CLOSE(pipeFD[0]);
+    VIR_FORCE_CLOSE(pipeFD[1]);
+    return ret;
+}
+
+
 static void virCommandThreadWorker(void *opaque)
 {
     virCommandTestDataPtr test = opaque;
@@ -1215,6 +1283,7 @@ mymain(void)
     DO_TEST(test22);
     DO_TEST(test23);
     DO_TEST(test24);
+    DO_TEST(test25);
 
     virMutexLock(&test->lock);
     if (test->running) {