fcrypt: consider the environment (TMPDIR) when looking for the tempor…

…ary directory

See ElektraInitiative#1973 for further details

doc/news/_preparation_next_release.md

@@ -108,6 +108,10 @@ Thanks to Michael Zronek and Vanessa Kos.
 
 - The `crypto` plugin now uses Elektra's `libinvoke` and the `base64` plugin in order to encode and decode Base64 strings. This improvement reduces code duplication between the two plugins. *(Peter Nirschl)*
 
+### fcrypt
+
+- The `fcrypt` plugin will consider the environment variable `TMPDIR` in order to detect its temporary directory. See [#1973] *(Peter Nirschl)*
+
 ### fstab
 
 - The `fstab` plugin now passes tests on musl builds. *(Lukas Winkler)*

src/plugins/fcrypt/README.md

@@ -134,10 +134,11 @@ Textmode can be disabled by setting `fcrypt/textmode` to `0` in the plugin confi
 ### Temporary Directory
 
 `fcrypt` uses the configuration option `fcrypt/tmpdir` to generate paths for temporary files during encryption and decryption.
-The path is forwarded to GPG via the `-o` option, so GPG will output to this path.
-The directory must be readable and writable by the user.
+If no such configuration option is provided, `fcrypt` will try to use the environment variable `TMPDIR`.
+If `TMPDIR` is not set in the environment, `/tmp` is used as default directory.
 
-`/tmp` is used as default value.
+The path of the temporary directory is forwarded to GPG via the `-o` option, so GPG will output to this path.
+The directory must be readable and writable by the user.
 
 We recommend to specify a path that is mounted to a RAM disk.
 It is advisable to set restrictive access rules to this path, so that other users on the system can not access it.

src/plugins/fcrypt/fcrypt.c

@@ -64,13 +64,26 @@ typedef struct _fcryptState fcryptState;
 static char * getTemporaryFileName (KeySet * conf, const char * file, int * fd)
 {
 	// read the temporary directory to use from the plugin configuration
-	const char * tmpDir = ELEKTRA_FCRYPT_DEFAULT_TMPDIR;
+	// NOTE the string contained in tmpDir must not be modified!
+	char * tmpDir = NULL;
 	Key * k = ksLookupByName (conf, ELEKTRA_FCRYPT_CONFIG_TMPDIR, 0);
 	if (k)
 	{
 		tmpDir = keyString (k);
 	}
 
+	if (!tmpDir)
+	{
+		// check the environment; returns NULL if no match is found
+		tmpDir = getenv ("TMPDIR");
+	}
+
+	if (!tmpDir)
+	{
+		// fallback
+		tmpDir = ELEKTRA_FCRYPT_DEFAULT_TMPDIR;
+	}
+
 	// extract the file name (base name) from the path
 	char * fileDup = strdup (file);
 	if (!fileDup) goto error;