CVE-2025-38017— fs/eventpoll: fix endless busy loop after timeout has expired

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

In the Linux kernel, the following vulnerability has been resolved: fs/eventpoll: fix endless busy loop after timeout has expired After commit 0a65bc27bd64 ("eventpoll: 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].

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Linux kernel 安全漏洞

Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于未设置超时标志，可能导致无限循环。

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