[PATCH AUTOSEL 4.9 1/4] drm: Use size_t type for len variable in drm_copy_field()

[Sasha Levin]

From: Javier Martinez Canillas <javierm@xxxxxxxxxx>

[ Upstream commit 94dc3471d1b2b58b3728558d0e3f264e9ce6ff59 ]

The strlen() function returns a size_t which is an unsigned int on 32-bit
arches and an unsigned long on 64-bit arches. But in the drm_copy_field()
function, the strlen() return value is assigned to an 'int len' variable.

Later, the len variable is passed as copy_from_user() third argument that
is an unsigned long parameter as well.

In theory, this can lead to an integer overflow via type conversion. Since
the assignment happens to a signed int lvalue instead of a size_t lvalue.

In practice though, that's unlikely since the values copied are set by DRM
drivers and not controlled by userspace. But using a size_t for len is the
correct thing to do anyways.

Signed-off-by: Javier Martinez Canillas <javierm@xxxxxxxxxx>
Tested-by: Peter Robinson <pbrobinson@xxxxxxxxx>
Reviewed-by: Thomas Zimmermann <tzimmermann@xxxxxxx>
Link: https://patchwork.freedesktop.org/patch/msgid/20220705100215.572498-2-javierm@xxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/gpu/drm/drm_ioctl.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
index 04b26ca06180..faa084ff4f17 100644
--- a/drivers/gpu/drm/drm_ioctl.c
+++ b/drivers/gpu/drm/drm_ioctl.c
@@ -419,7 +419,7 @@ EXPORT_SYMBOL(drm_invalid_op);
  */
 static int drm_copy_field(char __user *buf, size_t *buf_len, const char *value)
 {
-	int len;
+	size_t len;
 
 	/* don't overflow userbuf */
 	len = strlen(value);
-- 
2.35.1