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

[Greg Kroah-Hartman]

From: Kees Cook <keesc...@chromium.org>

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: sta...@vger.kernel.org
Acked-by: Scott Branden <scott.bran...@broadcom.com>
Signed-off-by: Kees Cook <keesc...@chromium.org>
Link: https://lore.kernel.org/r/20200724213640.389191-4-keesc...@chromium.org
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
 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;