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 firm ware_request_platform()")
Cc: stable@vger.kernel.org
Acked-by: Scott Branden <scott.branden@broadcom.com>
Signed-off-by: Kees Cook <redacted>
---
To aid in backporting, this change is made before moving
kernel_read_file() to separate header/source files.
---
 drivers/base/firmware_loader/fallback_platform.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/base/firmware_loader/fallback_platform.c b/drivers/base/firmware_loader/fallback_platform.c
index cdd2c9a9f38a..685edb7dd05a 100644
--- 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_priv *fw_priv, u32 opt_flags)
 	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;
 

-- 
2.25.1