linux-hardening - [PATCH] media: mxl5005s: Bounds check size used for max array index

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Date:   Sat,  4 Feb 2023 10:36:17 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Mauro Carvalho Chehab <mchehab@...nel.org>
Cc:     Kees Cook <keescook@...omium.org>,
        Colin Ian King <colin.i.king@...il.com>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: [PATCH] media: mxl5005s: Bounds check size used for max array index

The use of state->CH_Ctrl[i].size in a shift operation implies that its
value can be as much as 32, but the state->CH_Ctrl[i].val array is only
25 in size. Bounds check the size before shifting and looping. Fixes
warnings seen with GCC 13:

../drivers/media/tuners/mxl5005s.c: In function 'MXL_ControlWrite_Group.isra':
../drivers/media/tuners/mxl5005s.c:3450:70: warning: array subscript 32 is above array bounds of 'u16[25]' {aka 'short unsigned int[25]'} [-Warray-bounds=]
 3450 | state->CH_Ctrl[i].val[j] = (u8)((value >> j) & 0x01);
      |  ~~~~~~~~~~~~~~~~~~~~~^~~
../drivers/media/tuners/mxl5005s.c:238:13: note: while referencing 'val'
  238 |         u16 val[25];    /* Binary representation of Value */
      |             ^~~

Cc: Mauro Carvalho Chehab <mchehab@...nel.org>
Cc: Colin Ian King <colin.i.king@...il.com>
Cc: Hans Verkuil <hverkuil-cisco@...all.nl>
Cc: linux-media@...r.kernel.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 drivers/media/tuners/mxl5005s.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/media/tuners/mxl5005s.c b/drivers/media/tuners/mxl5005s.c
index 3a509038c8df..06dfab9fb8cb 100644
--- a/drivers/media/tuners/mxl5005s.c
+++ b/drivers/media/tuners/mxl5005s.c
@@ -3423,9 +3423,11 @@ static u16 MXL_ControlWrite_Group(struct dvb_frontend *fe, u16 controlNum,
 
 			if (controlNum == state->Init_Ctrl[i].Ctrl_Num) {
 
-				highLimit = 1 << state->Init_Ctrl[i].size;
+				u16 size = min_t(u16, state->Init_Ctrl[i].size,
+					       ARRAY_SIZE(state->Init_Ctrl[i].val));
+				highLimit = 1 << size;
 				if (value < highLimit) {
-					for (j = 0; j < state->Init_Ctrl[i].size; j++) {
+					for (j = 0; j < size; j++) {
 						state->Init_Ctrl[i].val[j] = (u8)((value >> j) & 0x01);
 						MXL_RegWriteBit(fe, (u8)(state->Init_Ctrl[i].addr[j]),
 							(u8)(state->Init_Ctrl[i].bit[j]),
@@ -3442,9 +3444,11 @@ static u16 MXL_ControlWrite_Group(struct dvb_frontend *fe, u16 controlNum,
 
 			if (controlNum == state->CH_Ctrl[i].Ctrl_Num) {
 
-				highLimit = 1 << state->CH_Ctrl[i].size;
+				u16 size = min_t(u16, state->CH_Ctrl[i].size,
+					       ARRAY_SIZE(state->CH_Ctrl[i].val));
+				highLimit = 1 << size;
 				if (value < highLimit) {
-					for (j = 0; j < state->CH_Ctrl[i].size; j++) {
+					for (j = 0; j < size; j++) {
 						state->CH_Ctrl[i].val[j] = (u8)((value >> j) & 0x01);
 						MXL_RegWriteBit(fe, (u8)(state->CH_Ctrl[i].addr[j]),
 							(u8)(state->CH_Ctrl[i].bit[j]),
-- 
2.34.1