linux-cve-announce - CVE-2025-38595: xen: fix UAF in dmabuf_exp_from

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Message-ID: <2025081918-CVE-2025-38595-9676@gregkh>
Date: Tue, 19 Aug 2025 19:18:41 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-38595: xen: fix UAF in dmabuf_exp_from_pages()

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

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

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

xen: fix UAF in dmabuf_exp_from_pages()

[dma_buf_fd() fixes; no preferences regarding the tree it goes through -
up to xen folks]

As soon as we'd inserted a file reference into descriptor table, another
thread could close it.  That's fine for the case when all we are doing is
returning that descriptor to userland (it's a race, but it's a userland
race and there's nothing the kernel can do about it).  However, if we
follow fd_install() with any kind of access to objects that would be
destroyed on close (be it the struct file itself or anything destroyed
by its ->release()), we have a UAF.

dma_buf_fd() is a combination of reserving a descriptor and fd_install().
gntdev dmabuf_exp_from_pages() calls it and then proceeds to access the
objects destroyed on close - starting with gntdev_dmabuf itself.

Fix that by doing reserving descriptor before anything else and do
fd_install() only when everything had been set up.

The Linux kernel CVE team has assigned CVE-2025-38595 to this issue.

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

	Issue introduced in 4.19 with commit a240d6e42e28c34fdc34b3a98ca838a31c939901 and fixed in 6.12.42 with commit e5907885260401bba300d4d18d79875c05b82651
	Issue introduced in 4.19 with commit a240d6e42e28c34fdc34b3a98ca838a31c939901 and fixed in 6.15.10 with commit 3edfd2353f301bfffd5ee41066e37320a59ccc2d
	Issue introduced in 4.19 with commit a240d6e42e28c34fdc34b3a98ca838a31c939901 and fixed in 6.16.1 with commit d59d49af4aeed9a81e673e37c26c6a3bacf1a181
	Issue introduced in 4.19 with commit a240d6e42e28c34fdc34b3a98ca838a31c939901 and fixed in 6.17-rc1 with commit 532c8b51b3a8676cbf533a291f8156774f30ea87

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-2025-38595
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/xen/gntdev-dmabuf.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/e5907885260401bba300d4d18d79875c05b82651
	https://git.kernel.org/stable/c/3edfd2353f301bfffd5ee41066e37320a59ccc2d
	https://git.kernel.org/stable/c/d59d49af4aeed9a81e673e37c26c6a3bacf1a181
	https://git.kernel.org/stable/c/532c8b51b3a8676cbf533a291f8156774f30ea87