Re: CVE-2026-31404: NFSD: Defer sub-object cleanup in export put callbacks

[yangerkun]

Hi all,

This commit has been reverted since it does not fix any problem, should 
this CVE be rejected too?


commit 516403d4d85607fdef3ca41d4a56b54e5566fa9a
Author: Yang Erkun <yangerkun@xxxxxxxxxx>
Date:   Wed May 13 10:42:52 2026 +0800

    Revert "NFSD: Defer sub-object cleanup in export put callbacks"

    This reverts commit 48db892356d6cb80f6942885545de4a6dd8d2a29.

Thanks,
Erkun.


在 2026/4/3 23:19, Greg Kroah-Hartman 写道:
> From: Greg Kroah-Hartman <gregkh@xxxxxxxxxx>
>
> Description
> ===========
>
> In the Linux kernel, the following vulnerability has been resolved:
>
> NFSD: Defer sub-object cleanup in export put callbacks
>
> svc_export_put() calls path_put() and auth_domain_put() immediately
> when the last reference drops, before the RCU grace period. RCU
> readers in e_show() and c_show() access both ex_path (via
> seq_path/d_path) and ex_client->name (via seq_escape) without
> holding a reference. If cache_clean removes the entry and drops the
> last reference concurrently, the sub-objects are freed while still
> in use, producing a NULL pointer dereference in d_path.
>
> Commit 2530766492ec ("nfsd: fix UAF when access ex_uuid or
> ex_stats") moved kfree of ex_uuid and ex_stats into the
> call_rcu callback, but left path_put() and auth_domain_put() running
> before the grace period because both may sleep and call_rcu
> callbacks execute in softirq context.
>
> Replace call_rcu/kfree_rcu with queue_rcu_work(), which defers the
> callback until after the RCU grace period and executes it in process
> context where sleeping is permitted. This allows path_put() and
> auth_domain_put() to be moved into the deferred callback alongside
> the other resource releases. Apply the same fix to expkey_put(),
> which has the identical pattern with ek_path and ek_client.
>
> A dedicated workqueue scopes the shutdown drain to only NFSD
> export release work items; flushing the shared
> system_unbound_wq would stall on unrelated work from other
> subsystems. nfsd_export_shutdown() uses rcu_barrier() followed
> by flush_workqueue() to ensure all deferred release callbacks
> complete before the export caches are destroyed.
>
> Reviwed-by: Jeff Layton <jlayton@xxxxxxxxxx>
>
> The Linux kernel CVE team has assigned CVE-2026-31404 to this issue.
>
>
> Affected and fixed versions
> ===========================
>
> 	Issue introduced in 6.14 with commit c224edca7af028828e2ad866b61d731b5e72b46d and fixed in 6.18.20 with commit 2829e80d29b627886d12b5ea40856d56b516e67d
> 	Issue introduced in 6.14 with commit c224edca7af028828e2ad866b61d731b5e72b46d and fixed in 6.19.10 with commit f5ab1bec5fa18731e0b1b1e60c9a68667ac73ea2
> 	Issue introduced in 6.14 with commit c224edca7af028828e2ad866b61d731b5e72b46d and fixed in 7.0-rc5 with commit 48db892356d6cb80f6942885545de4a6dd8d2a29
>
> 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-2026-31404
> 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/export.c
> 	fs/nfsd/export.h
> 	fs/nfsd/nfsctl.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/2829e80d29b627886d12b5ea40856d56b516e67d
> 	https://git.kernel.org/stable/c/f5ab1bec5fa18731e0b1b1e60c9a68667ac73ea2
> 	https://git.kernel.org/stable/c/48db892356d6cb80f6942885545de4a6dd8d2a29