linux-cve-announce - CVE-2025-21796: nfsd: clear acl_access/acl

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Message-ID: <2025022610-CVE-2025-21796-0133@gregkh>
Date: Wed, 26 Feb 2025 18:17:52 -0800
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2025-21796: nfsd: clear acl_access/acl_default after releasing them

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

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

nfsd: clear acl_access/acl_default after releasing them

If getting acl_default fails, acl_access and acl_default will be released
simultaneously. However, acl_access will still retain a pointer pointing
to the released posix_acl, which will trigger a WARNING in
nfs3svc_release_getacl like this:

------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: CPU: 26 PID: 3199 at lib/refcount.c:28
refcount_warn_saturate+0xb5/0x170
Modules linked in:
CPU: 26 UID: 0 PID: 3199 Comm: nfsd Not tainted
6.12.0-rc6-00079-g04ae226af01f-dirty #8
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
1.16.1-2.fc37 04/01/2014
RIP: 0010:refcount_warn_saturate+0xb5/0x170
Code: cc cc 0f b6 1d b3 20 a5 03 80 fb 01 0f 87 65 48 d8 00 83 e3 01 75
e4 48 c7 c7 c0 3b 9b 85 c6 05 97 20 a5 03 01 e8 fb 3e 30 ff <0f> 0b eb
cd 0f b6 1d 8a3
RSP: 0018:ffffc90008637cd8 EFLAGS: 00010282
RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff83904fde
RDX: dffffc0000000000 RSI: 0000000000000008 RDI: ffff88871ed36380
RBP: ffff888158beeb40 R08: 0000000000000001 R09: fffff520010c6f56
R10: ffffc90008637ab7 R11: 0000000000000001 R12: 0000000000000001
R13: ffff888140e77400 R14: ffff888140e77408 R15: ffffffff858b42c0
FS:  0000000000000000(0000) GS:ffff88871ed00000(0000)
knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000562384d32158 CR3: 000000055cc6a000 CR4: 00000000000006f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 ? refcount_warn_saturate+0xb5/0x170
 ? __warn+0xa5/0x140
 ? refcount_warn_saturate+0xb5/0x170
 ? report_bug+0x1b1/0x1e0
 ? handle_bug+0x53/0xa0
 ? exc_invalid_op+0x17/0x40
 ? asm_exc_invalid_op+0x1a/0x20
 ? tick_nohz_tick_stopped+0x1e/0x40
 ? refcount_warn_saturate+0xb5/0x170
 ? refcount_warn_saturate+0xb5/0x170
 nfs3svc_release_getacl+0xc9/0xe0
 svc_process_common+0x5db/0xb60
 ? __pfx_svc_process_common+0x10/0x10
 ? __rcu_read_unlock+0x69/0xa0
 ? __pfx_nfsd_dispatch+0x10/0x10
 ? svc_xprt_received+0xa1/0x120
 ? xdr_init_decode+0x11d/0x190
 svc_process+0x2a7/0x330
 svc_handle_xprt+0x69d/0x940
 svc_recv+0x180/0x2d0
 nfsd+0x168/0x200
 ? __pfx_nfsd+0x10/0x10
 kthread+0x1a2/0x1e0
 ? kthread+0xf4/0x1e0
 ? __pfx_kthread+0x10/0x10
 ret_from_fork+0x34/0x60
 ? __pfx_kthread+0x10/0x10
 ret_from_fork_asm+0x1a/0x30
 </TASK>
Kernel panic - not syncing: kernel: panic_on_warn set ...

Clear acl_access/acl_default after posix_acl_release is called to prevent
UAF from being triggered.

The Linux kernel CVE team has assigned CVE-2025-21796 to this issue.


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

	Issue introduced in 2.6.13 with commit a257cdd0e2179630d3201c32ba14d7fcb3c3a055 and fixed in 6.1.129 with commit 2e59b2b68782519560b3d6a41dd66a3d01a01cd3
	Issue introduced in 2.6.13 with commit a257cdd0e2179630d3201c32ba14d7fcb3c3a055 and fixed in 6.6.79 with commit 55d947315fb5f67a35e4e1d3e01bb886b9c6decf
	Issue introduced in 2.6.13 with commit a257cdd0e2179630d3201c32ba14d7fcb3c3a055 and fixed in 6.12.16 with commit f8d871523142f7895f250a856f8c4a4181614510
	Issue introduced in 2.6.13 with commit a257cdd0e2179630d3201c32ba14d7fcb3c3a055 and fixed in 6.13.4 with commit 1fd94884174bd20beb1773990fd3b1aa877688d9
	Issue introduced in 2.6.13 with commit a257cdd0e2179630d3201c32ba14d7fcb3c3a055 and fixed in 6.14-rc3 with commit 7faf14a7b0366f153284db0ad3347c457ea70136

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-2025-21796
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/nfs2acl.c
	fs/nfsd/nfs3acl.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/2e59b2b68782519560b3d6a41dd66a3d01a01cd3
	https://git.kernel.org/stable/c/55d947315fb5f67a35e4e1d3e01bb886b9c6decf
	https://git.kernel.org/stable/c/f8d871523142f7895f250a856f8c4a4181614510
	https://git.kernel.org/stable/c/1fd94884174bd20beb1773990fd3b1aa877688d9
	https://git.kernel.org/stable/c/7faf14a7b0366f153284db0ad3347c457ea70136