libcamera: utils: Support systems that lack secure_getenv and issetugid

Android provides neither secure_getenv() nor issetugid(). Enable
compilation on that platform by using a plain getenv(), as that seems to
be the best we can do.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Hirokazu Honda <hiroh@chromium.org>
Reviewed-by: Umang Jain <umang.jain@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

meson.build

@@ -33,6 +33,10 @@ if cc.has_header_symbol('execinfo.h', 'backtrace')
     config_h.set('HAVE_BACKTRACE', 1)
 endif
 
+if cc.has_header_symbol('unistd.h', 'issetugid')
+    config_h.set('HAVE_ISSETUGID', 1)
+endif
+
 if cc.has_header_symbol('stdlib.h', 'secure_getenv', prefix : '#define _GNU_SOURCE')
     config_h.set('HAVE_SECURE_GETENV', 1)
 endif

src/libcamera/utils.cpp

@@ -59,6 +59,10 @@ const char *basename(const char *path)
  * avoid vulnerabilities that could occur if set-user-ID or set-group-ID
  * programs accidentally trust the environment.
  *
+ * \note Not all platforms may support the features required to implement the
+ * secure execution check, in which case this function behaves as getenv(). A
+ * notable example of this is Android.
+ *
  * \return A pointer to the value in the environment or NULL if the requested
  * environment variable doesn't exist or if secure execution is required.
  */
@@ -67,9 +71,10 @@ char *secure_getenv(const char *name)
 #if HAVE_SECURE_GETENV
 	return ::secure_getenv(name);
 #else
+#if HAVE_ISSETUGID
 	if (issetugid())
 		return NULL;
-
+#endif
 	return getenv(name);
 #endif
 }