CVE-2025-40271 — fs/proc: fix uaf in proc_readdir_de()

Affected: Linux, Siemens RUGGEDCOM RST2428P

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.

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CVE-2025-40271 — fs/proc: fix uaf in proc_readdir_de()