CVE-2026-98366: RDMA/rxe: validate access flags before swapping the MR's PD

CVE-2026-98366: RDMA/rxe: validate access flags before swapping the MR's PD

[Greg Kroah-Hartman]

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

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

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

RDMA/rxe: validate access flags before swapping the MR's PD

rxe_rereg_user_mr() reassigns mr->ibmr.pd first and only then
validates the IB_MR_REREG_ACCESS argument:

	if (flags & IB_MR_REREG_PD) {
		rxe_put(old_pd);
		rxe_get(pd);
		mr->ibmr.pd = ibpd;
	}

	if (flags & IB_MR_REREG_ACCESS) {
		if (access & ~RXE_ACCESS_SUPPORTED_MR)
			return ERR_PTR(-EOPNOTSUPP);
		mr->access = access;
	}

Both flags pass the entry check because RXE_MR_REREG_SUPPORTED is
IB_MR_REREG_PD | IB_MR_REREG_ACCESS, so a caller can reach the access
check with mr->ibmr.pd already reassigned.

mr->ibmr.pd is owned by the core, which adjusts pd->usecnt only on the
success path: ib_uverbs_rereg_mr() jumps to put_new_uobj on a driver error
without undoing the reassignment, so mr->pd == new_pd while the usecnts
still charge the MR to orig_pd. ib_dereg_mr_user() then decrements
new_pd, whose count can reach zero while a memory window still references
it; uverbs_free_pd() frees the PD on that count alone and rxe_mw_cleanup()
writes to freed memory:

  BUG: KASAN: slab-use-after-free in __rxe_put+0x31/0xa0
  Write of size 4 at addr ffff8881301dd690 by task rxe_poc/591
   __rxe_put+0x31/0xa0
   rxe_mw_cleanup+0x42/0x200
   __rxe_cleanup+0x115/0x370
   rxe_dealloc_mw+0x4c/0x80
  Allocated by task 591:
   ib_uverbs_alloc_pd+0x258/0x540
  Freed by task 591:
   ib_dealloc_pd_user+0x174/0x210
   uverbs_free_pd+0x8d/0xc0
   ib_uverbs_dealloc_pd+0x18e/0x1d0

Validate the access flags before mutating any state so the callback either
applies every requested change or none.

The Linux kernel CVE team has assigned CVE-2026-98366 to this issue.


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

	Issue introduced in 6.5 with commit 544c7f62cf32db2bd358f1e8a40a98bf98fa2a5c and fixed in 6.6.158 with commit 08f12745cb72981aa2cabe214af0c7a42a856f0a
	Issue introduced in 6.5 with commit 544c7f62cf32db2bd358f1e8a40a98bf98fa2a5c and fixed in 6.12.112 with commit 7230cc456d4bb2221c20c5f1d22b38b8576aa16f
	Issue introduced in 6.5 with commit 544c7f62cf32db2bd358f1e8a40a98bf98fa2a5c and fixed in 6.18.54 with commit fe602c91a52e161ace4afd5bdb8f33270c554c6f
	Issue introduced in 6.5 with commit 544c7f62cf32db2bd358f1e8a40a98bf98fa2a5c and fixed in 7.2.8 with commit 4dd7a53f1c5b44693c26dac4b9b5bd5bb9d604c8
	Issue introduced in 6.5 with commit 544c7f62cf32db2bd358f1e8a40a98bf98fa2a5c and fixed in 7.3-rc4 with commit ae36a5b609ae79f4de966328b78d2584be9719a4

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-2026-98366
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/sw/rxe/rxe_verbs.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/08f12745cb72981aa2cabe214af0c7a42a856f0a
	https://git.kernel.org/stable/c/7230cc456d4bb2221c20c5f1d22b38b8576aa16f
	https://git.kernel.org/stable/c/fe602c91a52e161ace4afd5bdb8f33270c554c6f
	https://git.kernel.org/stable/c/4dd7a53f1c5b44693c26dac4b9b5bd5bb9d604c8
	https://git.kernel.org/stable/c/ae36a5b609ae79f4de966328b78d2584be9719a4