linux-cve-announce - CVE-2025-40271: fs/proc: fix uaf in proc_readdir

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [day] [month] [year] [list]

Message-ID: <2025120716-CVE-2025-40271-7612@gregkh>
Date: Sun,  7 Dec 2025 06:52:18 +0900
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-40271: fs/proc: fix uaf in proc_readdir_de()

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

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

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

fs/proc: fix uaf in proc_readdir_de()

Pde is erased from subdir rbtree through rb_erase(), but not set the node
to EMPTY, which may result in uaf access.  We should use RB_CLEAR_NODE()
set the erased node to EMPTY, then pde_subdir_next() will return NULL to
avoid uaf access.

We found an uaf issue while using stress-ng testing, need to run testcase
getdent and tun in the same time.  The steps of the issue is as follows:

1) use getdent to traverse dir /proc/pid/net/dev_snmp6/, and current
   pde is tun3;

2) in the [time windows] unregister netdevice tun3 and tun2, and erase
   them from rbtree.  erase tun3 first, and then erase tun2.  the
   pde(tun2) will be released to slab;

3) continue to getdent process, then pde_subdir_next() will return
   pde(tun2) which is released, it will case uaf access.

CPU 0                                      |    CPU 1
-------------------------------------------------------------------------
traverse dir /proc/pid/net/dev_snmp6/      |   unregister_netdevice(tun->dev)   //tun3 tun2
sys_getdents64()                           |
  iterate_dir()                            |
    proc_readdir()                         |
      proc_readdir_de()                    |     snmp6_unregister_dev()
        pde_get(de);                       |       proc_remove()
        read_unlock(&proc_subdir_lock);    |         remove_proc_subtree()
                                           |           write_lock(&proc_subdir_lock);
        [time window]                      |           rb_erase(&root->subdir_node, &parent->subdir);
                                           |           write_unlock(&proc_subdir_lock);
        read_lock(&proc_subdir_lock);      |
        next = pde_subdir_next(de);        |
        pde_put(de);                       |
        de = next;    //UAF                |

rbtree of dev_snmp6
                        |
                    pde(tun3)
                     /    \
                  NULL  pde(tun2)

The Linux kernel CVE team has assigned CVE-2025-40271 to this issue.


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

	Fixed in 5.4.302 with commit 1d1596d68a6f11d28f677eedf6cf5b17dbfeb491
	Fixed in 5.10.247 with commit c81d0385500446efe48c305bbb83d47f2ae23a50
	Fixed in 5.15.197 with commit 4cba73c4c89219beef7685a47374bf88b1022369
	Fixed in 6.1.159 with commit 6f2482745e510ae1dacc9b090194b9c5f918d774
	Fixed in 6.6.117 with commit 67272c11f379d9aa5e0f6b16286b9d89b3f76046
	Fixed in 6.12.59 with commit 623bb26127fb581a741e880e1e1a47d79aecb6f8
	Fixed in 6.17.9 with commit 03de7ff197a3d0e17d0d5c58fdac99a63cba8110
	Fixed in 6.18 with commit 895b4c0c79b092d732544011c3cecaf7322c36a1

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-2025-40271
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/proc/generic.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/1d1596d68a6f11d28f677eedf6cf5b17dbfeb491
	https://git.kernel.org/stable/c/c81d0385500446efe48c305bbb83d47f2ae23a50
	https://git.kernel.org/stable/c/4cba73c4c89219beef7685a47374bf88b1022369
	https://git.kernel.org/stable/c/6f2482745e510ae1dacc9b090194b9c5f918d774
	https://git.kernel.org/stable/c/67272c11f379d9aa5e0f6b16286b9d89b3f76046
	https://git.kernel.org/stable/c/623bb26127fb581a741e880e1e1a47d79aecb6f8
	https://git.kernel.org/stable/c/03de7ff197a3d0e17d0d5c58fdac99a63cba8110
	https://git.kernel.org/stable/c/895b4c0c79b092d732544011c3cecaf7322c36a1