Re: [PATCH v3] staging: vme_user: validate slave window size against buffer size

[Greg KH <gregkh@linuxfoundation.org>]

On Sat, May 09, 2026 at 06:07:21PM +0900, Rion Kiguchi wrote:
> The VME_SET_SLAVE ioctl in drivers/staging/vme_user/vme_user.c accepts
> a user-controlled slave.size and forwards it to vme_slave_set() without
> comparing it against image[minor].size_buf. The slave-image kernel
> buffer is allocated at probe time with a fixed size of PCI_BUF_SIZE
> (0x20000 / 128 KiB), but the configured VME window size can be made
> much larger via the ioctl.
> 
> The subsequent read() / write() handlers (vme_user_read /
> vme_user_write) clamp the I/O range against vme_get_size(), which
> returns the size the bridge driver has programmed for the window
> (i.e. the attacker-supplied slave.size). vme_get_size() does not
> consult size_buf, so an oversized window passes the existing bounds
> checks, and buffer_to_user() / buffer_from_user() then index
> image[minor].kern_buf with offsets beyond the actual allocation.
> 
> Result: a local user with read/write access to /dev/bus/vme/s* can
> trigger out-of-bounds read and write of the kernel slab adjacent to
> the slave-image buffer.
> 
> Fix: reject slave.size > size_buf in the VME_SET_SLAVE handler.
> With this check in place, the existing bounds checks in
> vme_user_read() / vme_user_write() against vme_get_size() are
> sufficient to prevent OOB access; no additional checks in
> buffer_to_user() / buffer_from_user() are needed.
> 
> Cc: stable@vger.kernel.org
> Assisted-by: Claude:claude-opus-4-7
> Signed-off-by: Rion Kiguchi <kiguchi.r.sec@gmail.com>
> ---
>  drivers/staging/vme_user/vme_user.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/staging/vme_user/vme_user.c b/drivers/staging/vme_user/vme_user.c
> index 11e25c2f6..6fd051f49 100644
> --- a/drivers/staging/vme_user/vme_user.c
> +++ b/drivers/staging/vme_user/vme_user.c
> @@ -394,6 +394,14 @@ static int vme_user_ioctl(struct inode *inode, struct file *file,
>  				return -EFAULT;
>  			}
>  
> +			/*
> +			 * Reject window sizes larger than the kernel buffer
> +			 * allocated at probe time, otherwise subsequent
> +			 * read/write would access memory beyond kern_buf.
> +			 */
> +			if (slave.size > image[minor].size_buf)
> +				return -EINVAL;
> +
>  			/* XXX	We do not want to push aspace, cycle and width
>  			 *	to userspace as they are
>  			 */
> @@ -401,7 +409,6 @@ static int vme_user_ioctl(struct inode *inode, struct file *file,
>  				slave.enable, slave.vme_addr, slave.size,
>  				image[minor].pci_buf, slave.aspace,
>  				slave.cycle);
> -
>  			break;
>  		}
>  		break;
> -- 
> 2.43.0
> 
> 

Hi,

This is the friendly patch-bot of Greg Kroah-Hartman.  You have sent him
a patch that has triggered this response.  He used to manually respond
to these common problems, but in order to save his sanity (he kept
writing the same thing over and over, yet to different people), I was
created.  Hopefully you will not take offence and will fix the problem
in your patch and resubmit it so that it can be accepted into the Linux
kernel tree.

You are receiving this message because of the following common error(s)
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If you wish to discuss this problem further, or you have questions about
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