[PATCH 6.6.y] media: av7110: fix a spectre vulnerability

[Artem Dinaburg <artem@trailofbits.com>]

From: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

[ Upstream commit 458ea1c0be991573ec436aa0afa23baacfae101a ]

As warned by smatch:
	drivers/staging/media/av7110/av7110_ca.c:270 dvb_ca_ioctl() warn: potential spectre issue 'av7110->ci_slot' [w] (local cap)

There is a spectre-related vulnerability at the code. Fix it.

[ Backport to 6.6.y: added the explicit linux/nospec.h include required
  by the older source. ]

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Assisted-by: LLM
Signed-off-by: Artem Dinaburg <artem@trailofbits.com>
---
Hi Greg, Sasha, and media av7110 maintainers,

I am working through the small CVE backports still missing from 6.6.y.
This one addresses CVE-2024-50289. It masks the validated CI-slot index
before using it in the av7110 array lookup.

The fix is already present in 6.12.y, 6.18.y, and 7.2.y, but not in 6.6.y.
This fix also affects 6.1.y, which will need a separate backport; this
submission contains only the 6.6.y patch.
The target-specific adjustment is recorded in the bracketed note above.

Could you please queue it for 6.6.y?

CVE: CVE-2024-50289
Upstream: 458ea1c0be991573ec436aa0afa23baacfae101a

AI assistance: An LLM helped identify, adapt, and validate this backport; I
reviewed the resulting code and validation evidence.

Thanks,
Artem Dinaburg

 drivers/staging/media/av7110/av7110.h    |  4 +++-
 drivers/staging/media/av7110/av7110_ca.c | 26 ++++++++++++++++--------
 2 files changed, 21 insertions(+), 9 deletions(-)

diff --git a/drivers/staging/media/av7110/av7110.h b/drivers/staging/media/av7110/av7110.h
index 809d938ae1667f..f77766008b973d 100644
--- a/drivers/staging/media/av7110/av7110.h
+++ b/drivers/staging/media/av7110/av7110.h
@@ -86,6 +86,8 @@ struct infrared {
 	u32			ir_config;
 };
 
+#define MAX_CI_SLOTS	2
+
 /* place to store all the necessary device information */
 struct av7110 {
 
@@ -166,7 +168,7 @@ struct av7110 {
 
 	/* CA */
 
-	struct ca_slot_info	ci_slot[2];
+	struct ca_slot_info	ci_slot[MAX_CI_SLOTS];
 
 	enum av7110_video_mode	vidmode;
 	struct dmxdev		dmxdev;
diff --git a/drivers/staging/media/av7110/av7110_ca.c b/drivers/staging/media/av7110/av7110_ca.c
index c1338e074a3dc1..642af03fbac810 100644
--- a/drivers/staging/media/av7110/av7110_ca.c
+++ b/drivers/staging/media/av7110/av7110_ca.c
@@ -12,6 +12,7 @@
  */
 
 #include <linux/kernel.h>
+#include <linux/nospec.h>
 #include <linux/types.h>
 #include <linux/delay.h>
 #include <linux/fs.h>
@@ -26,23 +27,28 @@
 
 void CI_handle(struct av7110 *av7110, u8 *data, u16 len)
 {
+	unsigned slot_num;
+
 	dprintk(8, "av7110:%p\n",av7110);
 
 	if (len < 3)
 		return;
 	switch (data[0]) {
 	case CI_MSG_CI_INFO:
-		if (data[2] != 1 && data[2] != 2)
+		if (data[2] != 1 && data[2] != MAX_CI_SLOTS)
 			break;
+
+		slot_num = array_index_nospec(data[2] - 1, MAX_CI_SLOTS);
+
 		switch (data[1]) {
 		case 0:
-			av7110->ci_slot[data[2] - 1].flags = 0;
+			av7110->ci_slot[slot_num].flags = 0;
 			break;
 		case 1:
-			av7110->ci_slot[data[2] - 1].flags |= CA_CI_MODULE_PRESENT;
+			av7110->ci_slot[slot_num].flags |= CA_CI_MODULE_PRESENT;
 			break;
 		case 2:
-			av7110->ci_slot[data[2] - 1].flags |= CA_CI_MODULE_READY;
+			av7110->ci_slot[slot_num].flags |= CA_CI_MODULE_READY;
 			break;
 		}
 		break;
@@ -264,15 +270,19 @@ static int dvb_ca_ioctl(struct file *file, unsigned int cmd, void *parg)
 	case CA_GET_SLOT_INFO:
 	{
 		struct ca_slot_info *info=(struct ca_slot_info *)parg;
+		unsigned int slot_num;
 
 		if (info->num < 0 || info->num > 1) {
 			mutex_unlock(&av7110->ioctl_mutex);
 			return -EINVAL;
 		}
-		av7110->ci_slot[info->num].num = info->num;
-		av7110->ci_slot[info->num].type = FW_CI_LL_SUPPORT(av7110->arm_app) ?
-							CA_CI_LINK : CA_CI;
-		memcpy(info, &av7110->ci_slot[info->num], sizeof(struct ca_slot_info));
+		slot_num = array_index_nospec(info->num, MAX_CI_SLOTS);
+
+		av7110->ci_slot[slot_num].num = info->num;
+		av7110->ci_slot[slot_num].type = FW_CI_LL_SUPPORT(av7110->arm_app) ?
+						 CA_CI_LINK : CA_CI;
+		memcpy(info, &av7110->ci_slot[slot_num],
+		       sizeof(struct ca_slot_info));
 		break;
 	}
 
-- 
2.39.5