[PATCH] media: solo6x10: Check for out of bounds chip_id

[Kees Cook <kees@kernel.org>]

Clang with CONFIG_UBSAN_SHIFT=y noticed a condition where a signed type
(literal "1" is an "int") could end up being shifted beyond 32 bits,
so instrumentation was added (and due to the double is_tw286x() call
seen via inlining), Clang decides the second one must now be undefined
behavior and elides the rest of the function[1]. This is a known problem
with Clang (that is still being worked on), but we can avoid the entire
problem by actually checking the existing max chip ID, and now there is
no runtime instrumentation added at all since everything is known to be
within bounds.

Additionally use an unsigned value for the shift to remove the
instrumentation even without the explicit bounds checking.

Link: https://github.com/ClangBuiltLinux/linux/issues/2144 [1]
Suggested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Kees Cook <kees@kernel.org>
---
Cc: Bluecherry Maintainers <maintainers@bluecherrydvr.com>
Cc: Andrey Utkin <andrey_utkin@fastmail.com>
Cc: Ismael Luceno <ismael@iodev.co.uk>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: <linux-media@vger.kernel.org>
---
 drivers/media/pci/solo6x10/solo6x10-tw28.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/media/pci/solo6x10/solo6x10-tw28.c b/drivers/media/pci/solo6x10/solo6x10-tw28.c
index 1b7c22a9bc94..da7b45dea5bc 100644
--- a/drivers/media/pci/solo6x10/solo6x10-tw28.c
+++ b/drivers/media/pci/solo6x10/solo6x10-tw28.c
@@ -166,7 +166,7 @@ static const u8 tbl_tw2865_pal_template[] = {
 	0x64, 0x51, 0x40, 0xaf, 0xFF, 0xF0, 0x00, 0xC0,
 };
 
-#define is_tw286x(__solo, __id) (!(__solo->tw2815 & (1 << __id)))
+#define is_tw286x(__solo, __id) (!(__solo->tw2815 & (1U << __id)))
 
 static u8 tw_readbyte(struct solo_dev *solo_dev, int chip_id, u8 tw6x_off,
 		      u8 tw_off)
@@ -686,6 +686,9 @@ int tw28_set_ctrl_val(struct solo_dev *solo_dev, u32 ctrl, u8 ch,
 	chip_num = ch / 4;
 	ch %= 4;
 
+	if (chip_num >= TW_NUM_CHIP)
+		return -EINVAL;
+
 	if (val > 255 || val < 0)
 		return -ERANGE;
 
@@ -758,6 +761,9 @@ int tw28_get_ctrl_val(struct solo_dev *solo_dev, u32 ctrl, u8 ch,
 	chip_num = ch / 4;
 	ch %= 4;
 
+	if (chip_num >= TW_NUM_CHIP)
+		return -EINVAL;
+
 	switch (ctrl) {
 	case V4L2_CID_SHARPNESS:
 		/* Only 286x has sharpness */
-- 
2.34.1