re: [PATCH v4] i2c: xgene-slimpro: Fix out-of-bounds bug in xgene_slimpro_i2c_xfer()

[Zheng Yejian]

> The data->block[0] variable comes from user and is a number between
> 0-255. Without proper check, the variable may be very large to cause
> an out-of-bounds when performing memcpy in slimpro_i2c_blkwr.
> 
> Fix this bug by checking the value of writelen.
> 
> Fixes: f6505fbabc42 ("i2c: add SLIMpro I2C device driver on APM X-Gene
> platform")
> Signed-off-by: Wei Chen <harperchen1110@xxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> ---
> Changes in v2:
>  - Put length check inside slimpro_i2c_blkwr
> Changes in v3:
>  - Correct the format of patch
> Changes in v4:
>  - CC stable email address
> 
>  drivers/i2c/busses/i2c-xgene-slimpro.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/i2c/busses/i2c-xgene-slimpro.c
> b/drivers/i2c/busses/i2c-xgene-slimpro.c
> index bc9a3e7e0c96..0f7263e2276a 100644
> --- a/drivers/i2c/busses/i2c-xgene-slimpro.c
> +++ b/drivers/i2c/busses/i2c-xgene-slimpro.c
> @@ -308,6 +308,9 @@ static int slimpro_i2c_blkwr(struct slimpro_i2c_dev
> *ctx, u32 chip,
> 	u32 msg[3];
> 	int rc;
>  
> +	if (writelen > I2C_SMBUS_BLOCK_MAX)
> +		return -EINVAL;
> +
> 	memcpy(ctx->dma_buffer, data, writelen);

Hi, I'm not sure if following case is problematic since I'm not familiar
with i2c :)

See following code path, when data->block[0] == I2C_SMBUS_BLOCK_MAX,
writelen == I2C_SMBUS_BLOCK_MAX + 1, and there seems no out-of-bounds
problem when performing memcpy() since the size of 'ctx->dma_buffer' is
I2C_SMBUS_BLOCK_MAX + 1. However after this patch, this case would fail,
is this expected?

  xgene_slimpro_i2c_xfer() {
    case I2C_SMBUS_BLOCK_DATA:
      ret = slimpro_i2c_blkwr(ctx, ..., data->block[0] + 1, &data->block[0]);
  }

> 	paddr = dma_map_single(ctx->dev, ctx->dma_buffer, writelen,
> 			       DMA_TO_DEVICE);
> -- 
> 2.25.1

--

Best regards,
Zheng Yejian