[PATCH AUTOSEL 6.1 01/33] drm/displayid: add displayid_get_header() and check bounds better

Sasha Levin
2023-05-01T03:10:44Z

From: Jani Nikula <jani.nikula@intel.com>

[ Upstream commit 5bacecc3c56131c31f18b23d366f2184328fd9cf ]

Add a helper to get a pointer to struct displayid_header. To be
pedantic, add buffer overflow checks to not touch the base if that
itself would overflow.

Cc: Iaroslav Boliukin <iam@lach.pw>
Cc: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Reviewed-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/4a03b3a5132642d3cdb6d4c2641422955a917292.1676580180.git.jani.nikula@intel.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/gpu/drm/drm_displayid.c | 17 ++++++++++++++++-
1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_displayid.c b/drivers/gpu/drm/drm_displayid.c
index 38ea8203df45b..7d03159dc1461 100644
--- a/drivers/gpu/drm/drm_displayid.c
+++ b/drivers/gpu/drm/drm_displayid.c
@@ -7,13 +7,28 @@
#include <drm/drm_edid.h>
#include <drm/drm_print.h>

+static const struct displayid_header *
+displayid_get_header(const u8 *displayid, int length, int index)
+{
+ const struct displayid_header *base;
+
+ if (sizeof(*base) > length - index)
+ return ERR_PTR(-EINVAL);
+
+ base = (const struct displayid_header *)&displayid[index];
+
+ return base;
+}
+
static int validate_displayid(const u8 *displayid, int length, int idx)
{
int i, dispid_length;
u8 csum = 0;
const struct displayid_header *base;

- base = (const struct displayid_header *)&displayid[idx];
+ base = displayid_get_header(displayid, length, idx);
+ if (IS_ERR(base))
+ return PTR_ERR(base);

DRM_DEBUG_KMS("base revision 0x%x, length %d, %d %d\n",
base->rev, base->bytes, base->prod_id, base->ext_count);
--
2.39.2