Re: [PATCH] w1: ds28e17: reject an oversize length on an I2C block read

[Andi Shyti <andi.shyti@kernel.org>]

Hi Maoyi,

On Mon, Jun 29, 2026 at 08:10:43PM +0800, Maoyi Xie wrote:
> w1_f19_i2c_master_transfer() is the master_xfer for the DS28E17 1-Wire
> to I2C bridge. On an I2C_M_RECV_LEN read, it takes the length from the
> device. The downstream slave puts a length byte in buf[0]. The driver
> then reads that many bytes into buf[1] with w1_f19_i2c_read().

yes, I2C_M_RECV_LEN is tied to the SMBUS so that it needs to be
capped to 32 bytes.

> buf[0] is controlled by the device and can be 0 to 255.
> w1_f19_i2c_read() only rejects a zero count. The caller buffer is
> I2C_SMBUS_BLOCK_MAX + 2, so 34 bytes. A length above 32 makes the read
> run past it, up to about 222 bytes out of bounds.
> 
> The SMBus core does check buf[0] against I2C_SMBUS_BLOCK_MAX. That
> check runs after master_xfer returns. By then the write is already
> done. i2c-algo-bit rejects an oversize length before it copies, and
> returns -EPROTO.
> 
> Reject a length above I2C_SMBUS_BLOCK_MAX at both RECV_LEN sites, the
> same way i2c-algo-bit does.
> 
> Fixes: ebc4768ac497 ("add w1_ds28e17 driver for the DS28E17 Onewire to I2C master bridge")
> Cc: stable@vger.kernel.org

Cc: <stable@vger.kernel.org> # v4.15+

> Signed-off-by: Maoyi Xie <maoyixie.tju@gmail.com>

Reviewed-by: Andi Shyti <andi.shyti@kernel.org>

This should go through Krzysztof, I guess.

Thanks,
Andi