CVE-2025-39881

Description

In the Linux kernel, the following vulnerability has been resolved:kernfs: Fix UAF in polling when open file is releasedA use-after-free (UAF) vulnerability was identified in the PSI (PressureStall Information) monitoring mechanism:BUG: KASAN: slab-use-after-free in psi_trigger_poll+0x3c/0x140Read of size 8 at addr ffff3de3d50bd308 by task systemd/1psi_trigger_poll+0x3c/0x140cgroup_pressure_poll+0x70/0xa0cgroup_file_poll+0x8c/0x100kernfs_fop_poll+0x11c/0x1c0ep_item_poll.isra.0+0x188/0x2c0Allocated by task 1:cgroup_file_open+0x88/0x388kernfs_fop_open+0x73c/0xaf0do_dentry_open+0x5fc/0x1200vfs_open+0xa0/0x3f0do_open+0x7e8/0xd08path_openat+0x2fc/0x6b0do_filp_open+0x174/0x368Freed by task 8462:cgroup_file_release+0x130/0x1f8kernfs_drain_open_files+0x17c/0x440kernfs_drain+0x2dc/0x360kernfs_show+0x1b8/0x288cgroup_file_show+0x150/0x268cgroup_pressure_write+0x1dc/0x340cgroup_file_write+0x274/0x548Reproduction Steps:1. Open test/cpu.pressure and establish epoll monitoring2. Disable monitoring: echo 0 > test/cgroup.pressure3. Re-enable monitoring: echo 1 > test/cgroup.pressureThe race condition occurs because:1. When cgroup.pressure is disabled (echo 0 > cgroup.pressure), it: - Releases PSI triggers via cgroup_file_release() - Frees of->priv through kernfs_drain_open_files()2. While epoll still holds reference to the file and continues polling3. Re-enabling (echo 1 > cgroup.pressure) accesses freed of->privepollingdisable/enable cgroup.pressurefd=open(cpu.pressure)while(1)...epoll_waitkernfs_fop_pollkernfs_get_active = trueecho 0 > cgroup.pressure...cgroup_file_showkernfs_show// inactive knkernfs_drain_open_filescft->release(of);kfree(ctx);...kernfs_get_active = falseecho 1 > cgroup.pressurekernfs_showkernfs_activate_one(kn);kernfs_fop_pollkernfs_get_active = truecgroup_file_pollpsi_trigger_poll// UAF...end: close(fd)To address this issue, introduce kernfs_get_active_of() for kernfs openfiles to obtain active references. This function will fail if the open filehas been released. Replace kernfs_get_active() with kernfs_get_active_of()to prevent further operations on released file descriptors.

Risk Information

Associated Vulnerability

Patch Details

References

https://nvd.nist.gov/vuln/detail/CVE-2023-1234
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-1234