linux-cve-announce - CVE-2025-39790: bus: mhi: host: Detect events pointing to unexpected TREs

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Message-ID: <2025091152-CVE-2025-39790-f6db@gregkh>
Date: Thu, 11 Sep 2025 18:57:08 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-39790: bus: mhi: host: Detect events pointing to unexpected TREs

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

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

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

bus: mhi: host: Detect events pointing to unexpected TREs

When a remote device sends a completion event to the host, it contains a
pointer to the consumed TRE. The host uses this pointer to process all of
the TREs between it and the host's local copy of the ring's read pointer.
This works when processing completion for chained transactions, but can
lead to nasty results if the device sends an event for a single-element
transaction with a read pointer that is multiple elements ahead of the
host's read pointer.

For instance, if the host accesses an event ring while the device is
updating it, the pointer inside of the event might still point to an old
TRE. If the host uses the channel's xfer_cb() to directly free the buffer
pointed to by the TRE, the buffer will be double-freed.

This behavior was observed on an ep that used upstream EP stack without
'commit 6f18d174b73d ("bus: mhi: ep: Update read pointer only after buffer
is written")'. Where the device updated the events ring pointer before
updating the event contents, so it left a window where the host was able to
access the stale data the event pointed to, before the device had the
chance to update them. The usual pattern was that the host received an
event pointing to a TRE that is not immediately after the last processed
one, so it got treated as if it was a chained transaction, processing all
of the TREs in between the two read pointers.

This commit aims to harden the host by ensuring transactions where the
event points to a TRE that isn't local_rp + 1 are chained.

[mani: added stable tag and reworded commit message]

The Linux kernel CVE team has assigned CVE-2025-39790 to this issue.

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

	Issue introduced in 5.7 with commit 1d3173a3bae7039b765a0956e3e4bf846dbaacb8 and fixed in 5.15.190 with commit 7b3f0e3b60c27f4fcb69927d84987e5fd6240530
	Issue introduced in 5.7 with commit 1d3173a3bae7039b765a0956e3e4bf846dbaacb8 and fixed in 6.1.149 with commit 4079c6c59705b96285219b9efc63cab870d757b7
	Issue introduced in 5.7 with commit 1d3173a3bae7039b765a0956e3e4bf846dbaacb8 and fixed in 6.6.103 with commit 5e17429679a8545afe438ce7a82a13a54e8ceabb
	Issue introduced in 5.7 with commit 1d3173a3bae7039b765a0956e3e4bf846dbaacb8 and fixed in 6.12.44 with commit 2ec99b922f4661521927eeada76f431eebfbabc4
	Issue introduced in 5.7 with commit 1d3173a3bae7039b765a0956e3e4bf846dbaacb8 and fixed in 6.16.4 with commit 44e1a079e18f78d6594a715b0c6d7e18c656f7b9
	Issue introduced in 5.7 with commit 1d3173a3bae7039b765a0956e3e4bf846dbaacb8 and fixed in 6.17-rc1 with commit 5bd398e20f0833ae8a1267d4f343591a2dd20185

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-2025-39790
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/bus/mhi/host/main.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/7b3f0e3b60c27f4fcb69927d84987e5fd6240530
	https://git.kernel.org/stable/c/4079c6c59705b96285219b9efc63cab870d757b7
	https://git.kernel.org/stable/c/5e17429679a8545afe438ce7a82a13a54e8ceabb
	https://git.kernel.org/stable/c/2ec99b922f4661521927eeada76f431eebfbabc4
	https://git.kernel.org/stable/c/44e1a079e18f78d6594a715b0c6d7e18c656f7b9
	https://git.kernel.org/stable/c/5bd398e20f0833ae8a1267d4f343591a2dd20185