published December 8, 2025
In the Linux kernel, the following vulnerability has been resolved:
9p/trans_fd: p9_fd_request: kick rx thread if EPOLLIN
p9_read_work() doesn't set Rworksched and doesn't do schedule_work(m->rq)
if list_empty(&m->req_list).
However, if the pipe is full, we need to read more data and this used to
work prior to commit aaec5a95d59615 ("pipe_read: don't wake up the writer
if the pipe is still full").
p9_read_work() does p9_fd_read() -> ... -> anon_pipe_read() which (before
the commit above) triggered the unnecessary wakeup. This wakeup calls
p9_pollwake() which kicks p9_poll_workfn() -> p9_poll_mux(), p9_poll_mux()
will notice EPOLLIN and schedule_work(&m->rq).
This no longer happens after the optimization above, change p9_fd_request()
to use p9_poll_mux() instead of only checking for EPOLLOUT.