From: Tianchu Chen <flynnnchen@tencent.com>

Discovered by Atuin - Automated Vulnerability Discovery Engine.

The 'len' variable is calculated as 'min(32, trans->len + 1)',
which includes the 1-byte command header.

When copying data from 'trans->tx_buf' to 'ch341->tx_buf + 1', using 'len'
as the length is incorrect because:

1. It causes an out-of-bounds read from 'trans->tx_buf' (which has size
   'trans->len', i.e., 'len - 1' in this context).
2. It can cause an out-of-bounds write to 'ch341->tx_buf' if 'len' is
   CH341_PACKET_LENGTH (32). Writing 32 bytes to ch341->tx_buf + 1
   overflows the buffer.

Fix this by copying 'len - 1' bytes.

Fixes: 8846739f52af ("spi: add ch341a usb2spi driver")
Signed-off-by: Tianchu Chen <flynnnchen@tencent.com>
---
 drivers/spi/spi-ch341.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/spi/spi-ch341.c b/drivers/spi/spi-ch341.c
index 46bc208f2..79d2f9ab4 100644
--- a/drivers/spi/spi-ch341.c
+++ b/drivers/spi/spi-ch341.c
@@ -78,7 +78,7 @@ static int ch341_transfer_one(struct spi_controller *host,
 
 	ch341->tx_buf[0] = CH341A_CMD_SPI_STREAM;
 
-	memcpy(ch341->tx_buf + 1, trans->tx_buf, len);
+	memcpy(ch341->tx_buf + 1, trans->tx_buf, len - 1);
 
 	ret = usb_bulk_msg(ch341->udev, ch341->write_pipe, ch341->tx_buf, len,
 			   NULL, CH341_DEFAULT_TIMEOUT);
-- 
2.39.5

On Fri, 28 Nov 2025 16:06:30 +0800, Tianchu Chen wrote:
> Discovered by Atuin - Automated Vulnerability Discovery Engine.
> 
> The 'len' variable is calculated as 'min(32, trans->len + 1)',
> which includes the 1-byte command header.
> 
> When copying data from 'trans->tx_buf' to 'ch341->tx_buf + 1', using 'len'
> as the length is incorrect because:
> 
> [...]

Applied to

   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git for-next

Thanks!

[1/1] spi: ch341: fix out-of-bounds memory access in ch341_transfer_one
      commit: 545d1287e40a55242f6ab68bcc1ba3b74088b1bc

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark

On Fri, Nov 28, 2025 at 04:06:30PM +0800, Tianchu Chen wrote:
> From: Tianchu Chen <flynnnchen@tencent.com>
> 
> Discovered by Atuin - Automated Vulnerability Discovery Engine.
> 
> The 'len' variable is calculated as 'min(32, trans->len + 1)',
> which includes the 1-byte command header.
> 
> When copying data from 'trans->tx_buf' to 'ch341->tx_buf + 1', using 'len'
> as the length is incorrect because:
> 
> 1. It causes an out-of-bounds read from 'trans->tx_buf' (which has size
>    'trans->len', i.e., 'len - 1' in this context).
> 2. It can cause an out-of-bounds write to 'ch341->tx_buf' if 'len' is
>    CH341_PACKET_LENGTH (32). Writing 32 bytes to ch341->tx_buf + 1
>    overflows the buffer.
> 
> Fix this by copying 'len - 1' bytes.
> 
> Fixes: 8846739f52af ("spi: add ch341a usb2spi driver")
> Signed-off-by: Tianchu Chen <flynnnchen@tencent.com>
> ---
>  drivers/spi/spi-ch341.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/spi/spi-ch341.c b/drivers/spi/spi-ch341.c
> index 46bc208f2..79d2f9ab4 100644
> --- a/drivers/spi/spi-ch341.c
> +++ b/drivers/spi/spi-ch341.c
> @@ -78,7 +78,7 @@ static int ch341_transfer_one(struct spi_controller *host,
>  
>  	ch341->tx_buf[0] = CH341A_CMD_SPI_STREAM;
>  
> -	memcpy(ch341->tx_buf + 1, trans->tx_buf, len);
> +	memcpy(ch341->tx_buf + 1, trans->tx_buf, len - 1);
>  
>  	ret = usb_bulk_msg(ch341->udev, ch341->write_pipe, ch341->tx_buf, len,
>  			   NULL, CH341_DEFAULT_TIMEOUT);
> -- 
> 2.39.5
> 

Hi,

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