[PATCH] media: dvb-usb-v2: gl861: Fix null-ptr-deref in gl861_i2c_master_xfer

[PATCH] media: dvb-usb-v2: gl861: Fix null-ptr-deref in gl861_i2c_master_xfer

[Zhang Shurong]

In gl861_i2c_master_xfer, msg is controlled by user. When msg[i].buf
is null and msg[i].len is zero, former checks on msg[i].buf would be
passed. Malicious data finally reach gl861_i2c_master_xfer. If accessing
msg[i].buf[0] without sanity check, null ptr deref would happen.
We add check on msg[i].len to prevent crash.

Similar commit:
commit 0ed554fd769a
("media: dvb-usb: az6027: fix null-ptr-deref in az6027_i2c_xfer()")

Signed-off-by: Zhang Shurong <zhang_shurong@foxmail.com>
---
 drivers/media/usb/dvb-usb-v2/gl861.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/media/usb/dvb-usb-v2/gl861.c b/drivers/media/usb/dvb-usb-v2/gl861.c
index 0c434259c36f..a552b646d407 100644
--- a/drivers/media/usb/dvb-usb-v2/gl861.c
+++ b/drivers/media/usb/dvb-usb-v2/gl861.c
@@ -97,7 +97,7 @@ static int gl861_i2c_master_xfer(struct i2c_adapter *adap, struct i2c_msg msg[],
 	/* XXX: I2C adapter maximum data lengths are not tested */
 	if (num == 1 && !(msg[0].flags & I2C_M_RD)) {
 		/* I2C write */
-		if (msg[0].len < 2 || msg[0].len > sizeof(ctx->buf)) {
+		if (msg[0].len == 0 || msg[0].len > sizeof(ctx->buf)) {
 			ret = -EOPNOTSUPP;
 			goto err;
 		}
@@ -120,7 +120,7 @@ static int gl861_i2c_master_xfer(struct i2c_adapter *adap, struct i2c_msg msg[],
 	} else if (num == 2 && !(msg[0].flags & I2C_M_RD) &&
 		   (msg[1].flags & I2C_M_RD)) {
 		/* I2C write + read */
-		if (msg[0].len > 1 || msg[1].len > sizeof(ctx->buf)) {
+		if (msg[0].len != 1 || msg[1].len > sizeof(ctx->buf)) {
 			ret = -EOPNOTSUPP;
 			goto err;
 		}
-- 
2.30.2

Re: [PATCH] media: dvb-usb-v2: gl861: Fix null-ptr-deref in gl861_i2c_master_xfer

[Akihiro TSUKADA]

Is the first chunk of your patch really necessary?
`msg[0].len < 2` includes the `msg[0].len == 0` case,
so the `msg.buf == NULL && msg.len == 0` case is (seemed to me)
safely ejected as it is.

> --- a/drivers/media/usb/dvb-usb-v2/gl861.c
> +++ b/drivers/media/usb/dvb-usb-v2/gl861.c
> @@ -97,7 +97,7 @@ static int gl861_i2c_master_xfer(struct i2c_adapt
> 
> er *adap, struct i2c_msg msg[],
>  	/* XXX: I2C adapter maximum data lengths are not tested */
>  	if (num == 1 && !(msg[0].flags & I2C_M_RD)) {
>  		/* I2C write */
> -		if (msg[0].len < 2 || msg[0].len > sizeof(ctx->buf)) {
> +		if (msg[0].len == 0 || msg[0].len > sizeof(ctx->buf)) {
>  			ret = -EOPNOTSUPP;
>  			goto err;
>  		}

regards,
akihiro

Re: [PATCH] media: dvb-usb-v2: gl861: Fix null-ptr-deref in gl861_i2c_master_xfer

[Zhang Shurong]

You are right. I am very sorry for my mistake and I will send another patch fix this.

> Is the first chunk of your patch really necessary?
> `msg[0].len < 2` includes the `msg[0].len == 0` case,
> so the `msg.buf == NULL && msg.len == 0` case is (seemed to me)
> safely ejected as it is.
> 
>> --- a/drivers/media/usb/dvb-usb-v2/gl861.c
>> +++ b/drivers/media/usb/dvb-usb-v2/gl861.c
>> @@ -97,7 +97,7 @@ static int gl861_i2c_master_xfer(struct i2c_adapt
>> 
>> er *adap, struct i2c_msg msg[],
>> /* XXX: I2C adapter maximum data lengths are not tested */
>> if (num == 1 && !(msg[0].flags & I2C_M_RD)) {
>> /* I2C write */
>> - if (msg[0].len < 2 || msg[0].len > sizeof(ctx->buf)) {
>> + if (msg[0].len == 0 || msg[0].len > sizeof(ctx->buf)) {
>> ret = -EOPNOTSUPP;
>> goto err;
>> }
> 
> regards,
> akihiro
>