CVE-2026-93267: RDMA/core: Fix potential use after free in uverbs_free_dmah()

CVE-2026-93267: RDMA/core: Fix potential use after free in uverbs_free_dmah()

[Greg Kroah-Hartman]

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

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

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

RDMA/core: Fix potential use after free in uverbs_free_dmah()

When accessing a dmah via the netlink path the only synchronization
mechanism for the said dmah is rdma_restrack_get().
Currently, rdma_restrack_del() is invoked at the end of
uverbs_free_dmah(), which is too late, since by that point
vendor-specific resources associated with the dmah might already be
freed. This can leave a short window where the dmah remains accessible
through restrack, leading to a potential use-after-free.

Fix this by moving the rdma_restrack_begin_del() call to the start of
uverbs_free_dmah(), ensuring that the dmah is removed from restrack
before its internal resources are released. This guarantees that no new
users hold references to a dmah that is in the process of destruction.

In addition, this change preserves the intended inverted order
between create and destroy routines: resources are added to
restrack at the end of successful creation, and hence shall be removed
from the restrack first thing during the destruction flow, which keeps
the lifecycle management consistent and predictable.

The Linux kernel CVE team has assigned CVE-2026-93267 to this issue.


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

	Issue introduced in 6.17 with commit d83edab562a496a42720902a1d2effccd05c37c5 and fixed in 6.18.52 with commit 8b22722f45a29a7c0900b1d4d0bc5da5492ece10
	Issue introduced in 6.17 with commit d83edab562a496a42720902a1d2effccd05c37c5 and fixed in 7.2.6 with commit bfc119a40c04bbe3daad826f2160ccbfae6c64ce
	Issue introduced in 6.17 with commit d83edab562a496a42720902a1d2effccd05c37c5 and fixed in 7.3-rc1 with commit 2696626a0be5877f445fb647c25ef43930c777e6

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-2026-93267
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/infiniband/core/uverbs_std_types_dmah.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/8b22722f45a29a7c0900b1d4d0bc5da5492ece10
	https://git.kernel.org/stable/c/bfc119a40c04bbe3daad826f2160ccbfae6c64ce
	https://git.kernel.org/stable/c/2696626a0be5877f445fb647c25ef43930c777e6