misc: Introduce internal function ssh_dir_writeable()

The introduced internal function checks if the provided path is for an
existing directory which is accessible for writing.

Signed-off-by: Anderson Toshiyuki Sasaki <ansasaki@redhat.com>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>

include/libssh/misc.h

@@ -26,6 +26,7 @@
 char *ssh_get_user_home_dir(void);
 char *ssh_get_local_username(void);
 int ssh_file_readaccess_ok(const char *file);
+int ssh_dir_writeable(const char *path);
 
 char *ssh_path_expand_tilde(const char *d);
 char *ssh_path_expand_escape(ssh_session session, const char *s);

src/misc.c

@@ -130,6 +130,31 @@ int ssh_file_readaccess_ok(const char *file) {
   return 1;
 }
 
+/**
+ * @brief Check if the given path is an existing directory and that is
+ * accessible for writing.
+ *
+ * @param[in] path Path to the directory to be checked
+ *
+ * @return Return 1 if the directory exists and is accessible; 0 otherwise
+ * */
+int ssh_dir_writeable(const char *path)
+{
+    struct _stat buffer;
+    int rc;
+
+    rc = _stat(path, &buffer);
+    if (rc < 0) {
+        return 0;
+    }
+
+    if ((buffer.st_mode & _S_IFDIR) && (buffer.st_mode & _S_IWRITE)) {
+        return 1;
+    }
+
+    return 0;
+}
+
 #define SSH_USEC_IN_SEC         1000000LL
 #define SSH_SECONDS_SINCE_1601  11644473600LL
 
@@ -247,6 +272,31 @@ int ssh_file_readaccess_ok(const char *file)
     return 1;
 }
 
+/**
+ * @brief Check if the given path is an existing directory and that is
+ * accessible for writing.
+ *
+ * @param[in] path Path to the directory to be checked
+ *
+ * @return Return 1 if the directory exists and is accessible; 0 otherwise
+ * */
+int ssh_dir_writeable(const char *path)
+{
+    struct stat buffer;
+    int rc;
+
+    rc = stat(path, &buffer);
+    if (rc < 0) {
+        return 0;
+    }
+
+    if (S_ISDIR(buffer.st_mode) && (buffer.st_mode & S_IWRITE)) {
+        return 1;
+    }
+
+    return 0;
+}
+
 char *ssh_get_local_username(void)
 {
     struct passwd pwd;

tests/unittests/torture_misc.c

@@ -19,6 +19,7 @@
 
 #define TORTURE_TEST_DIR "/usr/local/bin/truc/much/.."
 
+const char template[] = "temp_dir_XXXXXX";
 
 static int setup(void **state)
 {
@@ -363,6 +364,51 @@ static void torture_ssh_analyze_banner(void **state) {
     ssh_free(session);
 }
 
+static void torture_ssh_dir_writeable(UNUSED_PARAM(void **state))
+{
+    char *tmp_dir = NULL;
+    int rc = 0;
+    FILE *file = NULL;
+    char buffer[256];
+
+    tmp_dir = torture_make_temp_dir(template);
+    assert_non_null(tmp_dir);
+
+    rc = ssh_dir_writeable(tmp_dir);
+    assert_int_equal(rc, 1);
+
+    /* Create a file */
+    snprintf(buffer, sizeof(buffer), "%s/a", tmp_dir);
+
+    file = fopen(buffer, "w");
+    assert_non_null(file);
+
+    fprintf(file, "Hello world!\n");
+    fclose(file);
+
+    /* Negative test for checking a normal file */
+    rc = ssh_dir_writeable(buffer);
+    assert_int_equal(rc, 0);
+
+    /* Negative test for non existent file */
+    snprintf(buffer, sizeof(buffer), "%s/b", tmp_dir);
+    rc = ssh_dir_writeable(buffer);
+    assert_int_equal(rc, 0);
+
+#ifndef _WIN32
+    /* Negative test for directory without write permission */
+    rc = ssh_mkdir(buffer, 0400);
+    assert_return_code(rc, errno);
+
+    rc = ssh_dir_writeable(buffer);
+    assert_int_equal(rc, 0);
+#endif
+
+    torture_rmdirs(tmp_dir);
+
+    SAFE_FREE(tmp_dir);
+}
+
 int torture_run_tests(void) {
     int rc;
     struct CMUnitTest tests[] = {
@@ -381,6 +427,7 @@ int torture_run_tests(void) {
         cmocka_unit_test(torture_timeout_elapsed),
         cmocka_unit_test(torture_timeout_update),
         cmocka_unit_test(torture_ssh_analyze_banner),
+        cmocka_unit_test(torture_ssh_dir_writeable),
     };
 
     ssh_init();