[v2,1/2] drm: Use size_t type for len variable in drm_copy_field()

Commit Message

Javier Martinez Canillas July 5, 2022, 10:02 a.m. UTC

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 <[e-mail]>
Tested-by: Peter Robinson <[e-mail]>
Reviewed-by: Thomas Zimmermann <[e-mail]>
---

Changes in v2:
- Add Peter Robinson Tested-by and Thomas Zimmermann Reviewed-by tags.

 drivers/gpu/drm/drm_ioctl.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Patch

diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
index 8faad23dc1d8..e1b9a03e619c 100644
--- a/drivers/gpu/drm/drm_ioctl.c
+++ b/drivers/gpu/drm/drm_ioctl.c
@@ -472,7 +472,7 @@  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);