Introduce a SafeFreePool() that doesn't assert on NULL

* On release/consumer hardware, FreePool(NULL) is valid and does nothing,
  but on DEBUG builds, it may trigger an assert.
* We therefore introduce SafeFreePool() to take care of these scenarios.
* Closes #5.

Author: pbatard

include/uefi-driver/uefi_support.h

@@ -1,6 +1,6 @@
 /* uefi_support.h - UEFI support declarations */
 /*
- *  Copyright © 2014-2021 Pete Batard <pete@akeo.ie>
+ *  Copyright © 2014-2023 Pete Batard <pete@akeo.ie>
  *
  *  This program is free software: you can redistribute it and/or modify
  *  it under the terms of the GNU General Public License as published by
@@ -137,6 +137,12 @@ static __inline UINTN _SafeStrSize(CONST CHAR16* String, CONST CHAR8* File,
 
 #define SafeStrSize(s) _SafeStrSize(s, __FILE__, __LINE__)
 
+/*
+ * Secure FreePool that doesn't assert on NULL and sets the pointer
+ * passed as parameter to NULL after freeing it.
+ */
+#define SafeFreePool(p) if (p != NULL) { FreePool(p), p = NULL; }
+
 /*
  * EDK2 does not provide a StrDup call, so we define one.
  */

uefi-driver/uefi_bridge.c

@@ -1,6 +1,6 @@
 /* uefi_bridge.c - libntfs-3g interface for UEFI */
 /*
- *  Copyright © 2021 Pete Batard <pete@akeo.ie>
+ *  Copyright © 2021-2023 Pete Batard <pete@akeo.ie>
  *
  *  Parts taken from lowntfs-3g.c:
  *  Copyright © 2005-2007 Yura Pakhuchiy
@@ -629,7 +629,7 @@ NtfsFreeFile(EFI_NTFS_FILE* File)
 		return;
 	/* Only destroy a file that has no refs */
 	if (File->RefCount <= 0) {
-		FreePool(File->Path);
+		SafeFreePool(File->Path);
 		FreePool(File);
 	}
 }

uefi-driver/uefi_driver.c

@@ -1,6 +1,6 @@
 /* uefi_driver.c - ntfs-3g UEFI filesystem driver */
 /*
- *  Copyright © 2014-2021 Pete Batard <pete@akeo.ie>
+ *  Copyright © 2014-2023 Pete Batard <pete@akeo.ie>
  *  Based on iPXE's efi_driver.c and efi_file.c:
  *  Copyright © 2011,2013 Michael Brown <mbrown@fensystems.co.uk>
  *
@@ -108,8 +108,7 @@ static VOID
 FreeFsInstance(EFI_FS* Instance) {
 	if (Instance == NULL)
 		return;
-	if (Instance->DevicePathString != NULL)
-		FreePool(Instance->DevicePathString);
+	SafeFreePool(Instance->DevicePathString);
 	FreePool(Instance);
 }
 

uefi-driver/uefi_file.c

@@ -192,7 +192,7 @@ FileOpen(EFI_FILE_HANDLE This, EFI_FILE_HANDLE* New,
 		/* NB: This call only destroys the file if RefCount = 0 */
 		NtfsFreeFile(NewFile);
 	}
-	FreePool(Path);
+	SafeFreePool(Path);
 	return Status;
 }