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HIGH

fs/proc: fix uaf in proc_readdir_de()

Published Dec 6, 2025

Description

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)

Affected products

Remediation

Red Hat statement

The vulnerability is a race condition in /proc directory enumeration, where a proc_dir_entry can be freed after rb_erase() but still referenced because the rbtree node is not cleared. A local unprivileged attacker can trigger a use-after-free by running getdents() (that calls proc_readdir_de()) in parallel with rapid creation and removal of network-related proc entries (e.g., tun devices). In practice this leads to a kernel NULL-pointer dereference or slab-UAF crash. Reliable exploitation beyond denial-of-service is unlikely due to the narrow timing window, but theoretically possible. The bug could be triggered by the local attacker with the ability to create and remove network devices (e.g. CAP_NET_ADMIN).

Red Hat mitigation

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.

Metrics

Weaknesses (1)

CWE-825

References (14)

Change history (0)

No recorded changes yet.

Sources
CVE.org / MITRE
Status PUBLISHED
Assigner Linux
Published Dec 6, 2025
Updated Aug 5, 2026
Reserved Apr 16, 2025
Link CVE-2025-40271
CISA Vulnrichment
Updated Jun 16, 2026
NVD
Status Deferred
Modified Jul 30, 2026
Link CVE-2025-40271
Red Hat
Severity Moderate
Public date Dec 6, 2025
Links CVE-2025-40271 - Bugzilla