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eventpoll: propagate wakeup source creation failure in ep_modify()

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When EPOLL_CTL_MOD adds EPOLLWAKEUP, ep_modify() ignores the return
value of ep_create_wakeup_source(). If allocation fails, it returns
success with EPOLLWAKEUP set but no per-item wakeup source, so the
requested suspend protection is missing.

This can happen without fault injection on SELinux systems: creating
the wakeup source's sysfs nodes can require GFP_KERNEL_ACCOUNT
allocations for security.selinux xattrs, which can fail when the
caller's memory cgroup is over its limit.

Create the wakeup source before updating the event mask and data, and
return the error if creation fails. Leave any newly created per-epoll
source in place until ep_free(), as ep_insert() does on failure.

Fixes: 4d7e30d989 ("epoll: Add a flag, EPOLLWAKEUP, to prevent suspend while epoll events are ready")
Signed-off-by: Tianyi Chen <hi@tychen.cc>
Link: https://patch.msgid.link/179240281988.1700986.8309527041821666235@tychen.cc
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
This commit is contained in:
Tianyi Chen 2026-10-19 18:39:27 +09:00 committed by Christian Brauner
parent 90c9661246
commit 9f2b8f4a45
No known key found for this signature in database
GPG Key ID: 91C61BC06578DCA2
1 changed files with 13 additions and 5 deletions
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18
fs/eventpoll.c
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@ -1982,11 +1982,22 @@ static int ep_modify(struct eventpoll *ep, struct epitem *epi,
{
int pwake = 0;
poll_table pt;
int error;
lockdep_assert_irqs_enabled();
init_poll_funcptr(&pt, NULL);
/*
* Create the wakeup source before committing the new event mask.
* Leave the old mask and data unchanged if allocation fails.
*/
if ((event->events & EPOLLWAKEUP) && !ep_has_wakeup_source(epi)) {
error = ep_create_wakeup_source(epi);
if (error)
return error;
}
/*
* Set the new event interest mask before calling f_op->poll();
* otherwise we might miss an event that happens between the
@ -1994,12 +2005,9 @@ static int ep_modify(struct eventpoll *ep, struct epitem *epi,
*/
epi->event.events = event->events; /* need barrier below */
epi->event.data = event->data; /* protected by mtx */
if (epi->event.events & EPOLLWAKEUP) {
if (!ep_has_wakeup_source(epi))
ep_create_wakeup_source(epi);
} else if (ep_has_wakeup_source(epi)) {
if (!(epi->event.events & EPOLLWAKEUP) &&
ep_has_wakeup_source(epi))
ep_destroy_wakeup_source(epi);
}
/*
* The following barrier has two effects: