linux-kernel - [PATCH AUTOSEL 5.10 02/22] drm: Use size_t type for len variable in drm_copy

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Date:   Sun,  9 Oct 2022 19:55:20 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Javier Martinez Canillas <javierm@...hat.com>,
        Peter Robinson <pbrobinson@...il.com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Sasha Levin <sashal@...nel.org>,
        maarten.lankhorst@...ux.intel.com, mripard@...nel.org,
        airlied@...il.com, daniel@...ll.ch, dri-devel@...ts.freedesktop.org
Subject: [PATCH AUTOSEL 5.10 02/22] drm: Use size_t type for len variable in drm_copy_field()

From: Javier Martinez Canillas <javierm@...hat.com>

[ 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@...hat.com>
Tested-by: Peter Robinson <pbrobinson@...il.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@...e.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20220705100215.572498-2-javierm@redhat.com
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 4606cc938b36..a15d55d06510 100644
--- a/drivers/gpu/drm/drm_ioctl.c
+++ b/drivers/gpu/drm/drm_ioctl.c
@@ -473,7 +473,7 @@ 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