CVE-2026-72006: net/mlx5: free mlx5_st_idx_data on final dealloc

From: Greg Kroah-Hartman <[email protected]>

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

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

net/mlx5: free mlx5_st_idx_data on final dealloc

Workloads that repeatedly allocate and release mkeys carrying TPH
steering-tag hints (e.g. churning RDMA MRs) leak one
struct mlx5_st_idx_data per cycle; kmemleak flags it as unreferenced
and the kmalloc slab grows over time.

When the last reference to an ST table entry is dropped,
mlx5_st_dealloc_index() removed the entry from idx_xa but the backing
mlx5_st_idx_data allocation was never freed.

Free idx_data after the xa_erase() so the lifetime of the bookkeeping
struct matches the lifetime of the ST entry it tracks.

The Linux kernel CVE team has assigned CVE-2026-72006 to this issue.


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

	Issue introduced in 6.17 with commit 888a7776f4fb04c19bec70c737c61c2f383c6b1e and fixed in 6.18.40 with commit 262da8b6ea03d01ee7ed01ad309e4c89941f6b14
	Issue introduced in 6.17 with commit 888a7776f4fb04c19bec70c737c61c2f383c6b1e and fixed in 7.1.5 with commit 6eb4cf2fa8997f62c11e0006dc010a1fd89c5a75
	Issue introduced in 6.17 with commit 888a7776f4fb04c19bec70c737c61c2f383c6b1e and fixed in 7.2-rc4 with commit df6134b527a88b3e65ba6ae5073664af091d5fd2

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-2026-72006
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/net/ethernet/mellanox/mlx5/core/lib/st.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/262da8b6ea03d01ee7ed01ad309e4c89941f6b14
	https://git.kernel.org/stable/c/6eb4cf2fa8997f62c11e0006dc010a1fd89c5a75
	https://git.kernel.org/stable/c/df6134b527a88b3e65ba6ae5073664af091d5fd2