linux-kernel - Re: [PATCH] misc: ds1682: fix out-of-bounds access in EEPROM functions

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Message-ID: <5811d6f7-7305-4611-a06f-793343b0412e@wanadoo.fr>
Date: Sat, 9 Aug 2025 21:54:39 +0200
From: Christophe JAILLET <christophe.jaillet@...adoo.fr>
To: wajahat iqbal <wajahatiqbal22@...il.com>, gregkh@...uxfoundation.org
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH] misc: ds1682: fix out-of-bounds access in EEPROM
 functions

Le 09/08/2025 à 17:54, wajahat iqbal a écrit :
> Found a couple of issues in the ds1682 driver while reviewing the code:
> 
> The EEPROM read/write functions don't check if offset and count exceed
> the 10-byte EEPROM size, which could lead to out-of-bounds I2C access.
> 
> Also replaced sprintf with scnprintf in the sysfs show function for
> better safety.
> 
> For reads beyond EEPROM size, return 0. For writes, return -EINVAL if
> starting beyond bounds, otherwise truncate to fit within the EEPROM.
> 
> Signed-off-by: Wajahat Iqbal <wajahatiqbal22@...il.com>
> ---
>   drivers/misc/ds1682.c | 12 +++++++++++-
>   1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/misc/ds1682.c b/drivers/misc/ds1682.c
> index cb09e056531a..4cf4b43e5355 100644
> --- a/drivers/misc/ds1682.c
> +++ b/drivers/misc/ds1682.c
> @@ -92,7 +92,7 @@ static ssize_t ds1682_show(struct device *dev,
> struct device_attribute *attr,
>    * Special case: the 32 bit regs are time values with 1/4s
>    * resolution, scale them up to milliseconds
>    */
> - return sprintf(buf, "%llu\n", (sattr->nr == 4) ? (val * 250) : val);
> + return scnprintf(buf, PAGE_SIZE, "%llu\n", (sattr->nr == 4) ? (val *
> 250) : val);
>   }
> 
>   static ssize_t ds1682_store(struct device *dev, struct device_attribute *attr,
> @@ -163,6 +163,11 @@ static ssize_t ds1682_eeprom_read(struct file
> *filp, struct kobject *kobj,
>    dev_dbg(&client->dev, "ds1682_eeprom_read(p=%p, off=%lli, c=%zi)\n",
>    buf, off, count);
> 
> + if (off >= DS1682_EEPROM_SIZE)
> + return 0;
> + if (off + count > DS1682_EEPROM_SIZE)
> + count = DS1682_EEPROM_SIZE - off;
> +
>    rc = i2c_smbus_read_i2c_block_data(client, DS1682_REG_EEPROM + off,
>       count, buf);
>    if (rc < 0)
> @@ -180,6 +185,11 @@ static ssize_t ds1682_eeprom_write(struct file
> *filp, struct kobject *kobj,
>    dev_dbg(&client->dev, "ds1682_eeprom_write(p=%p, off=%lli, c=%zi)\n",
>    buf, off, count);
> 
> + if (off >= DS1682_EEPROM_SIZE)
> + return -EINVAL;
> + if (off + count > DS1682_EEPROM_SIZE)
> + count = DS1682_EEPROM_SIZE - off;
> +
>    /* Write out to the device */
>    if (i2c_smbus_write_i2c_block_data(client, DS1682_REG_EEPROM + off,
>       count, buf) < 0)

Are these new tests really needed?

Isn't it already done the same way by the core, because of the ".size = 
DS1682_EEPROM_SIZE" in ds1682_eeprom_attr?

I'm' not really familiar with this code, but my understanding is that it 
goes thru sysfs_kf_bin_write() and sysfs_kf_bin_read().

CJ