CVE-2025-38017 Information

Jun 19, 2025 cve

Description

In the Linux kernel the following vulnerability has been resolved:

fs/eventpoll: fix endless busy loop after timeout has expired

After commit 0a65bc27bd64 (ventpoll: Set epoll timeout if it’s in the future) the following program would immediately enter a busy loop in the kernel:

int main() 
  int e = epoll_create1(0);
  struct epoll_event event = .events = EPOLLIN;
  epoll_ctl(e EPOLL_CTL_ADD 0 &event);
  const struct timespec timeout = .tv_nsec = 1;
  epoll_pwait2(e &event 1 &timeout 0);

This happens because the given (non-zero) timeout of 1 nanosecond usually expires before ep_poll() is entered and then ep_schedule_timeout() returns false but timed_out is never set because the code line that sets it is skipped. This quickly turns into a soft lockup RCU stalls and deadlocks inflicting severe headaches to the whole system.

When the timeout has expired we don’t need to schedule a hrtimer but we should set the timed_out variable. Therefore I suggest moving the ep_schedule_timeout() check into the timed_out expression instead of skipping it.

brauner: Note that there was an earlier fix by Joe Damato in response to my bug report in [1].

Reference

https://git.kernel.org/stable/c/7631dca012593c95d36199082546a24a0058fc50 https://git.kernel.org/stable/c/d9ec73301099ec5975505e1c3effbe768bab9490

CNNVD-202506-2151 (Published: 2025-06-18)

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