CVE-2026-74729: soc: aspeed: lpc-snoop: Fix usercopy overflow in snoop_file_read

From: Greg Kroah-Hartman <[email protected]>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

soc: aspeed: lpc-snoop: Fix usercopy overflow in snoop_file_read

put_fifo_with_discard() acts as both producer and consumer on the kfifo:
it calls kfifo_skip() (advances out) and kfifo_put() (advances in) from
the IRQ handler without synchronizing with snoop_file_read(), which also
consumes via kfifo_to_user(). On SMP systems this concurrent access can
leave (in - out) larger than the ring buffer, so __kfifo_to_user()'s clamp
to (in - out) is ineffective and kfifo_copy_to_user() can attempt a
copy_to_user() past the kmalloc-2k backing store:

  usercopy: Kernel memory exposure attempt detected from SLUB object
  'kmalloc-2k' (offset 0, size 2049)!
  kernel BUG at mm/usercopy.c!
  Call trace:
   usercopy_abort
   __check_heap_object
   __check_object_size
   kfifo_copy_to_user
   __kfifo_to_user
   snoop_file_read
   vfs_read

Serialize kfifo access with a per-channel spinlock shared between the
IRQ handler (producer) and the file reader (consumer).  Annotate @fifo
with __guarded_by(&lock) and opt the driver into context analysis so the
compiler enforces that all fifo access holds the lock.

The Linux kernel CVE team has assigned CVE-2026-74729 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 4.19 with commit 3772e5da445420543b25825ac2b5971f3743f6e8 and fixed in 7.1.9 with commit 131ab677b03349a5ae48da8722ec7075b37ec66e
	Issue introduced in 4.19 with commit 3772e5da445420543b25825ac2b5971f3743f6e8 and fixed in 7.2 with commit 1acef6d85bfd98bd9dfe1f08bffa397a4dda8a6f

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-74729
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	drivers/soc/aspeed/Makefile
	drivers/soc/aspeed/aspeed-lpc-snoop.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/131ab677b03349a5ae48da8722ec7075b37ec66e
	https://git.kernel.org/stable/c/1acef6d85bfd98bd9dfe1f08bffa397a4dda8a6f