[PATCH 5.7 380/393] firmware_loader: EFI firmware loader must handle pre-allocated buffer

[Greg Kroah-Hartman]

From: Kees Cook <keescook@xxxxxxxxxxxx>

commit 4fb60b158afd3ac9e0fe9975aa476213f5cc0a4d upstream.

The EFI platform firmware fallback would clobber any pre-allocated
buffers. Instead, correctly refuse to reallocate when too small (as
already done in the sysfs fallback), or perform allocation normally
when needed.

Fixes: e4c2c0ff00ec ("firmware: Add new platform fallback mechanism and firmware_request_platform()")
Cc: stable@xxxxxxxxxxxxxxx
Acked-by: Scott Branden <scott.branden@xxxxxxxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20200724213640.389191-4-keescook@xxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/base/firmware_loader/fallback_platform.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/drivers/base/firmware_loader/fallback_platform.c
+++ b/drivers/base/firmware_loader/fallback_platform.c
@@ -25,7 +25,10 @@ int firmware_fallback_platform(struct fw
 	if (rc)
 		return rc; /* rc == -ENOENT when the fw was not found */
 
-	fw_priv->data = vmalloc(size);
+	if (fw_priv->data && size > fw_priv->allocated_size)
+		return -ENOMEM;
+	if (!fw_priv->data)
+		fw_priv->data = vmalloc(size);
 	if (!fw_priv->data)
 		return -ENOMEM;