CVE-2026-89690: nfsd: defer vfree of compound ops to fix rpc_status UAF

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

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

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

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

nfsd: defer vfree of compound ops to fix rpc_status UAF

The rpc_status netlink dumpit walks every in-flight svc_rqst under
rcu_read_lock and, for NFSv4 requests, reads opnums out of
args->ops[]. But args->ops is a separate vmalloc buffer freed
synchronously by vfree() in nfsd4_release_compoundargs() at the end
of every compound. The dumpit's rcu_read_lock pins the svc_rqst
struct itself (freed via kfree_rcu), but nothing defers the vfree
of the ops buffer across the RCU grace period. A concurrent compound
completion can therefore free the buffer while the dumpit is reading
it — a use-after-free on vmalloc memory.

The trailing seqcount recheck (smp_load_acquire of rq_status_counter)
cannot undo a load that already retired against freed memory.

Fix by replacing vfree(args->ops) with kvfree_rcu_mightsleep(), which
defers the free until after an RCU grace period. This makes the
existing rcu_read_lock in the dumpit sufficient to protect the read.
The tradeoff is that completed compound ops buffers (up to
200 * sizeof(struct nfsd4_op)) persist in memory slightly longer,
across one grace period, before being reclaimed.

The Linux kernel CVE team has assigned CVE-2026-89690 to this issue.


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

	Issue introduced in 6.7 with commit bd9d6a3efa9709e653aafbeb859289feccb8e70c and fixed in 6.12.109 with commit 48f72aff24f7a7329209dc6cbc27c869f3e3595c
	Issue introduced in 6.7 with commit bd9d6a3efa9709e653aafbeb859289feccb8e70c and fixed in 6.18.50 with commit 6703199f4d7e7f37d6a726a849eb358e8fae72fb
	Issue introduced in 6.7 with commit bd9d6a3efa9709e653aafbeb859289feccb8e70c and fixed in 7.2.4 with commit 19413ccc45070a7270b9e25c2a258daf7f91de42
	Issue introduced in 6.7 with commit bd9d6a3efa9709e653aafbeb859289feccb8e70c and fixed in 7.3-rc1 with commit fca26a3fc19ed02278aa2a150af82d43db0302cb

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-2026-89690
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:
	fs/nfsd/nfs4xdr.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/48f72aff24f7a7329209dc6cbc27c869f3e3595c
	https://git.kernel.org/stable/c/6703199f4d7e7f37d6a726a849eb358e8fae72fb
	https://git.kernel.org/stable/c/19413ccc45070a7270b9e25c2a258daf7f91de42
	https://git.kernel.org/stable/c/fca26a3fc19ed02278aa2a150af82d43db0302cb