CVE-2026-43006: io_uring/rsrc: reject zero-length fixed buffer import

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Greg Kroah-Hartman <gregkh@kernel.org>

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

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

io_uring/rsrc: reject zero-length fixed buffer import

validate_fixed_range() admits buf_addr at the exact end of the
registered region when len is zero, because the check uses strict
greater-than (buf_end > imu->ubuf + imu->len).  io_import_fixed()
then computes offset == imu->len, which causes the bvec skip logic
to advance past the last bio_vec entry and read bv_offset from
out-of-bounds slab memory.

Return early from io_import_fixed() when len is zero.  A zero-length
import has no data to transfer and should not walk the bvec array
at all.

  BUG: KASAN: slab-out-of-bounds in io_import_reg_buf+0x697/0x7f0
  Read of size 4 at addr ffff888002bcc254 by task poc/103
  Call Trace:
   io_import_reg_buf+0x697/0x7f0
   io_write_fixed+0xd9/0x250
   __io_issue_sqe+0xad/0x710
   io_issue_sqe+0x7d/0x1100
   io_submit_sqes+0x86a/0x23c0
   __do_sys_io_uring_enter+0xa98/0x1590
  Allocated by task 103:
  The buggy address is located 12 bytes to the right of
   allocated 584-byte region [ffff888002bcc000, ffff888002bcc248)

The Linux kernel CVE team has assigned CVE-2026-43006 to this issue.


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

	Issue introduced in 6.15 with commit 8622b20f23ed165f48b8ca61503a107d17f8d585 and fixed in 6.18.22 with commit 040a1e7e0e2f01851fec1dd2d96906f8636a9f75
	Issue introduced in 6.15 with commit 8622b20f23ed165f48b8ca61503a107d17f8d585 and fixed in 6.19.12 with commit 40170fc1a79c1b2e68f09ae6aac687b7305ae6f4
	Issue introduced in 6.15 with commit 8622b20f23ed165f48b8ca61503a107d17f8d585 and fixed in 7.0 with commit 111a12b422a8cfa93deabaef26fec48237163214

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-2026-43006
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:
	io_uring/rsrc.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/040a1e7e0e2f01851fec1dd2d96906f8636a9f75
	https://git.kernel.org/stable/c/40170fc1a79c1b2e68f09ae6aac687b7305ae6f4
	https://git.kernel.org/stable/c/111a12b422a8cfa93deabaef26fec48237163214