CVE-2026-64426: io_uring/nop: fix file reference leak with IOSQE_FIXED_FILE

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

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

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

io_uring/nop: fix file reference leak with IOSQE_FIXED_FILE

NOP file-acquisition support choses between a fixed (registered) file and
a normal fget()'d file based on its own IORING_NOP_FIXED_FILE flag in
sqe->nop_flags. However, a request's REQ_F_FIXED_FILE is set
independently from the generic IOSQE_FIXED_FILE sqe flag during request
init, before the issue handler runs.

If a NOP is submitted with IOSQE_FIXED_FILE set (so REQ_F_FIXED_FILE is
set) but without IORING_NOP_FIXED_FILE, io_nop() takes the normal path
and grabs a real reference via io_file_get_normal(). On completion,
io_put_file() only drops the reference when REQ_F_FIXED_FILE is clear,
so the fget()'d file is never released and leaks:

  BUG: memory leak
  unreferenced object 0xffff88800f42c240 (size 176):
    kmem_cache_alloc_noprof+0x358/0x440
    alloc_empty_file+0x57/0x180
    path_openat+0x44/0x1e50
    do_file_open+0x121/0x200
    do_sys_openat2+0xa7/0x150
    __x64_sys_openat+0x82/0xf0

Decide between fixed and normal file acquisition from REQ_F_FIXED_FILE,
the same way io_assign_file() does for every other opcode, and fold
IORING_NOP_FIXED_FILE into REQ_F_FIXED_FILE at prep time.

The Linux kernel CVE team has assigned CVE-2026-64426 to this issue.


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

	Issue introduced in 6.13 with commit a85f31052bce52111b4e9d5a536003481d0421d0 and fixed in 6.18.39 with commit 722869fcff598fad20d5ab79c305897a7534708b
	Issue introduced in 6.13 with commit a85f31052bce52111b4e9d5a536003481d0421d0 and fixed in 7.1.4 with commit 7267717f35787167fcce4bc14f6ef3fa06682dcf
	Issue introduced in 6.13 with commit a85f31052bce52111b4e9d5a536003481d0421d0 and fixed in 7.2-rc1 with commit 2564ca2e31bd8ee8348362941af2ee4671e487ca

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-2026-64426
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/nop.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/722869fcff598fad20d5ab79c305897a7534708b
	https://git.kernel.org/stable/c/7267717f35787167fcce4bc14f6ef3fa06682dcf
	https://git.kernel.org/stable/c/2564ca2e31bd8ee8348362941af2ee4671e487ca