linux-cve-announce - CVE-2025-21731: nbd: don't allow reconnect after disconnect

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Message-ID: <2025022649-CVE-2025-21731-c18b@gregkh>
Date: Wed, 26 Feb 2025 18:06:26 -0800
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2025-21731: nbd: don't allow reconnect after disconnect

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

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

nbd: don't allow reconnect after disconnect

Following process can cause nbd_config UAF:

1) grab nbd_config temporarily;

2) nbd_genl_disconnect() flush all recv_work() and release the
initial reference:

  nbd_genl_disconnect
   nbd_disconnect_and_put
    nbd_disconnect
     flush_workqueue(nbd->recv_workq)
    if (test_and_clear_bit(NBD_RT_HAS_CONFIG_REF, ...))
     nbd_config_put
     -> due to step 1), reference is still not zero

3) nbd_genl_reconfigure() queue recv_work() again;

  nbd_genl_reconfigure
   config = nbd_get_config_unlocked(nbd)
   if (!config)
   -> succeed
   if (!test_bit(NBD_RT_BOUND, ...))
   -> succeed
   nbd_reconnect_socket
    queue_work(nbd->recv_workq, &args->work)

4) step 1) release the reference;

5) Finially, recv_work() will trigger UAF:

  recv_work
   nbd_config_put(nbd)
   -> nbd_config is freed
   atomic_dec(&config->recv_threads)
   -> UAF

Fix the problem by clearing NBD_RT_BOUND in nbd_genl_disconnect(), so
that nbd_genl_reconfigure() will fail.

The Linux kernel CVE team has assigned CVE-2025-21731 to this issue.


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

	Issue introduced in 4.12 with commit b7aa3d39385dc2d95899f9e379623fef446a2acd and fixed in 6.1.129 with commit e7343fa33751cb07c1c56b666bf37cfca357130e
	Issue introduced in 4.12 with commit b7aa3d39385dc2d95899f9e379623fef446a2acd and fixed in 6.6.76 with commit d208d2c52b652913b5eefc8ca434b0d6b757f68f
	Issue introduced in 4.12 with commit b7aa3d39385dc2d95899f9e379623fef446a2acd and fixed in 6.12.13 with commit a8ee6ecde2b7bfb58c8a3afe8a9d2b848f580739
	Issue introduced in 4.12 with commit b7aa3d39385dc2d95899f9e379623fef446a2acd and fixed in 6.13.2 with commit 9793bd5ae4bdbdb2dde401a3cab94a6bfd05e302
	Issue introduced in 4.12 with commit b7aa3d39385dc2d95899f9e379623fef446a2acd and fixed in 6.14-rc1 with commit 844b8cdc681612ff24df62cdefddeab5772fadf1

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-2025-21731
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/block/nbd.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/e7343fa33751cb07c1c56b666bf37cfca357130e
	https://git.kernel.org/stable/c/d208d2c52b652913b5eefc8ca434b0d6b757f68f
	https://git.kernel.org/stable/c/a8ee6ecde2b7bfb58c8a3afe8a9d2b848f580739
	https://git.kernel.org/stable/c/9793bd5ae4bdbdb2dde401a3cab94a6bfd05e302
	https://git.kernel.org/stable/c/844b8cdc681612ff24df62cdefddeab5772fadf1