linux-cve-announce - CVE-2024-26958: nfs: fix UAF in direct writes

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Date: Wed,  1 May 2024 07:21:48 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2024-26958: nfs: fix UAF in direct writes

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

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

nfs: fix UAF in direct writes

In production we have been hitting the following warning consistently

------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: CPU: 17 PID: 1800359 at lib/refcount.c:28 refcount_warn_saturate+0x9c/0xe0
Workqueue: nfsiod nfs_direct_write_schedule_work [nfs]
RIP: 0010:refcount_warn_saturate+0x9c/0xe0
PKRU: 55555554
Call Trace:
 <TASK>
 ? __warn+0x9f/0x130
 ? refcount_warn_saturate+0x9c/0xe0
 ? report_bug+0xcc/0x150
 ? handle_bug+0x3d/0x70
 ? exc_invalid_op+0x16/0x40
 ? asm_exc_invalid_op+0x16/0x20
 ? refcount_warn_saturate+0x9c/0xe0
 nfs_direct_write_schedule_work+0x237/0x250 [nfs]
 process_one_work+0x12f/0x4a0
 worker_thread+0x14e/0x3b0
 ? ZSTD_getCParams_internal+0x220/0x220
 kthread+0xdc/0x120
 ? __btf_name_valid+0xa0/0xa0
 ret_from_fork+0x1f/0x30

This is because we're completing the nfs_direct_request twice in a row.

The source of this is when we have our commit requests to submit, we
process them and send them off, and then in the completion path for the
commit requests we have

if (nfs_commit_end(cinfo.mds))
	nfs_direct_write_complete(dreq);

However since we're submitting asynchronous requests we sometimes have
one that completes before we submit the next one, so we end up calling
complete on the nfs_direct_request twice.

The only other place we use nfs_generic_commit_list() is in
__nfs_commit_inode, which wraps this call in a

nfs_commit_begin();
nfs_commit_end();

Which is a common pattern for this style of completion handling, one
that is also repeated in the direct code with get_dreq()/put_dreq()
calls around where we process events as well as in the completion paths.

Fix this by using the same pattern for the commit requests.

Before with my 200 node rocksdb stress running this warning would pop
every 10ish minutes.  With my patch the stress test has been running for
several hours without popping.

The Linux kernel CVE team has assigned CVE-2024-26958 to this issue.


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

	Fixed in 5.10.215 with commit 4595d90b5d2e
	Fixed in 5.15.154 with commit 80d24b308b7e
	Fixed in 6.1.84 with commit 3abc2d160ed8
	Fixed in 6.6.24 with commit e25447c35f87
	Fixed in 6.7.12 with commit 1daf52b5ffb2
	Fixed in 6.8.3 with commit cf54f66e1dd7
	Fixed in 6.9-rc1 with commit 17f46b803d4f

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-2024-26958
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:
	fs/nfs/direct.c
	fs/nfs/write.c
	include/linux/nfs_fs.h


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/4595d90b5d2ea5fa4d318d13f59055aa4bf3e7f5
	https://git.kernel.org/stable/c/80d24b308b7ee7037fc90d8ac99f6f78df0a256f
	https://git.kernel.org/stable/c/3abc2d160ed8213948b147295d77d44a22c88fa3
	https://git.kernel.org/stable/c/e25447c35f8745337ea8bc0c9697fcac14df8605
	https://git.kernel.org/stable/c/1daf52b5ffb24870fbeda20b4967526d8f9e12ab
	https://git.kernel.org/stable/c/cf54f66e1dd78990ec6b32177bca7e6ea2144a95
	https://git.kernel.org/stable/c/17f46b803d4f23c66cacce81db35fef3adb8f2af