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

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

[木口璃音]

This patch addresses the OOB read/write reported earlier
in the security@kernel.org thread (now handled publicly per
Greg's and Willy's guidance).

Tested on Linux 7.1.0-rc2 with KASAN; all three reproducers
fail with -EINVAL after applying this patch and produce no
KASAN splat.

From 506ecfc9b8608fb3a56477b8fd205238a1bf66ff Mon Sep 17 00:00:00 2001
From: Rion Kiguchi <kiguchi.r.sec@gmail.com>
Date: Sat, 9 May 2026 15:38:33 +0900
Subject: [PATCH] staging: vme_user: validate slave window size against buffer
 size

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() (the
configured window size, attacker-controlled) but never consult
size_buf. The slave I/O paths buffer_to_user() and buffer_from_user()
then index image[minor].kern_buf with *ppos values up to
image_size - 1, well 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. Also
add defensive bounds checks against size_buf in buffer_to_user() and
buffer_from_user() so that the I/O paths cannot exceed the
allocation even if a future ioctl path forgets to validate.

Reported-by: Pochix1103 <kiguchi.r.sec@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Rion Kiguchi <kiguchi.r.sec@gmail.com>
---
 drivers/staging/vme_user/vme_user.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/drivers/staging/vme_user/vme_user.c
b/drivers/staging/vme_user/vme_user.c
index 11e25c2f6..41b8d5b51 100644
--- a/drivers/staging/vme_user/vme_user.c
+++ b/drivers/staging/vme_user/vme_user.c
@@ -156,6 +156,11 @@ static ssize_t buffer_to_user(unsigned int minor,
char __user *buf,
 {
  void *image_ptr;

+ if (*ppos < 0 || (u64)*ppos >= image[minor].size_buf ||
+     count > image[minor].size_buf - (u64)*ppos) {
+ pr_warn_ratelimited("%s: out-of-bounds access\n", __func__);
+ return -EINVAL;
+ }
  image_ptr = image[minor].kern_buf + *ppos;
  if (copy_to_user(buf, image_ptr, (unsigned long)count))
  return -EFAULT;
@@ -168,6 +173,11 @@ static ssize_t buffer_from_user(unsigned int
minor, const char __user *buf,
 {
  void *image_ptr;

+ if (*ppos < 0 || (u64)*ppos >= image[minor].size_buf ||
+     count > image[minor].size_buf - (u64)*ppos) {
+ pr_warn_ratelimited("%s: out-of-bounds access\n", __func__);
+ return -EINVAL;
+ }
  image_ptr = image[minor].kern_buf + *ppos;
  if (copy_from_user(image_ptr, buf, (unsigned long)count))
  return -EFAULT;
@@ -394,6 +404,14 @@ 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 +419,6 @@ 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

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

[gregkh]

On Sat, May 09, 2026 at 03:58:45PM +0900, 木口璃音 wrote:
> This patch addresses the OOB read/write reported earlier
> in the security@kernel.org thread (now handled publicly per
> Greg's and Willy's guidance).
> 
> Tested on Linux 7.1.0-rc2 with KASAN; all three reproducers
> fail with -EINVAL after applying this patch and produce no
> KASAN splat.
> 
> >From 506ecfc9b8608fb3a56477b8fd205238a1bf66ff Mon Sep 17 00:00:00 2001
> From: Rion Kiguchi <kiguchi.r.sec@gmail.com>
> Date: Sat, 9 May 2026 15:38:33 +0900
> Subject: [PATCH] staging: vme_user: validate slave window size against buffer
>  size

This all doesn't belong in the body of the email, please just use git
send-email to send the patch.

> 
> 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() (the
> configured window size, attacker-controlled) but never consult
> size_buf. The slave I/O paths buffer_to_user() and buffer_from_user()
> then index image[minor].kern_buf with *ppos values up to
> image_size - 1, well 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. Also
> add defensive bounds checks against size_buf in buffer_to_user() and
> buffer_from_user() so that the I/O paths cannot exceed the
> allocation even if a future ioctl path forgets to validate.
> 
> Reported-by: Pochix1103 <kiguchi.r.sec@gmail.com>

Ok, but:

> Cc: stable@vger.kernel.org
> Signed-off-by: Rion Kiguchi <kiguchi.r.sec@gmail.com>

You don't have a reported-by and a signed-off-by for the same thing, if
you author and sign off, it's implied you are reporting the issue :)

Also, you have to document the AI tool you used to find and fix this as
per out documentation.

thanks,

greg k-h

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

[gregkh]

On Sat, May 09, 2026 at 03:58:45PM +0900, 木口璃音 wrote:
> diff --git a/drivers/staging/vme_user/vme_user.c
> b/drivers/staging/vme_user/vme_user.c
> index 11e25c2f6..41b8d5b51 100644
> --- a/drivers/staging/vme_user/vme_user.c
> +++ b/drivers/staging/vme_user/vme_user.c
> @@ -156,6 +156,11 @@ static ssize_t buffer_to_user(unsigned int minor,
> char __user *buf,
>  {
>   void *image_ptr;
> 
> + if (*ppos < 0 || (u64)*ppos >= image[minor].size_buf ||
> +     count > image[minor].size_buf - (u64)*ppos) {
> + pr_warn_ratelimited("%s: out-of-bounds access\n", __func__);
> + return -EINVAL;
> + }

Also the patch is corrupted :(