linux-cve-announce - CVE-2025-39819: fs/smb: Fix inconsistent refcnt update

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Message-ID: <2025091615-CVE-2025-39819-d3c9@gregkh>
Date: Tue, 16 Sep 2025 15:00:25 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-39819: fs/smb: Fix inconsistent refcnt update

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

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

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

fs/smb: Fix inconsistent refcnt update

A possible inconsistent update of refcount was identified in `smb2_compound_op`.
Such inconsistent update could lead to possible resource leaks.

Why it is a possible bug:
1. In the comment section of the function, it clearly states that the
reference to `cfile` should be dropped after calling this function.
2. Every control flow path would check and drop the reference to
`cfile`, except the patched one.
3. Existing callers would not handle refcount update of `cfile` if
-ENOMEM is returned.

To fix the bug, an extra goto label "out" is added, to make sure that the
cleanup logic would always be respected. As the problem is caused by the
allocation failure of `vars`, the cleanup logic between label "finished"
and "out" can be safely ignored. According to the definition of function
`is_replayable_error`, the error code of "-ENOMEM" is not recoverable.
Therefore, the replay logic also gets ignored.

The Linux kernel CVE team has assigned CVE-2025-39819 to this issue.


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

	Fixed in 6.1.150 with commit 3fc11ff13fbc2749871d6ac2141685cf54699997
	Fixed in 6.6.104 with commit 4191ea1f0bb3e27d65c5dcde7bd00e709ec67141
	Fixed in 6.12.45 with commit 4735f5991f51468b85affb8366b7067248457a71
	Fixed in 6.16.5 with commit cc82c6dff548f0066a51a6e577c7454e7d26a968
	Fixed in 6.17-rc4 with commit ab529e6ca1f67bcf31f3ea80c72bffde2e9e053e

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-2025-39819
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/smb/client/smb2inode.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/3fc11ff13fbc2749871d6ac2141685cf54699997
	https://git.kernel.org/stable/c/4191ea1f0bb3e27d65c5dcde7bd00e709ec67141
	https://git.kernel.org/stable/c/4735f5991f51468b85affb8366b7067248457a71
	https://git.kernel.org/stable/c/cc82c6dff548f0066a51a6e577c7454e7d26a968
	https://git.kernel.org/stable/c/ab529e6ca1f67bcf31f3ea80c72bffde2e9e053e