init/epoll: Fix a potential use-after-free
If UnregisterHandler() is called from inside a handler for an event that
has not yet been processed then that will result in a use-after-free.
Fix this by passing file descriptors to epoll_ctl() instead of pointers
to map elements.
Bug: 213617178
Change-Id: Ie62e3a299af964271ec24cd8fc2e794042b77ee6
Signed-off-by: Bart Van Assche <bvanassche@google.com>
diff --git a/init/epoll.cpp b/init/epoll.cpp
index 24d356d..dc21043 100644
--- a/init/epoll.cpp
+++ b/init/epoll.cpp
@@ -54,9 +54,7 @@
}
epoll_event ev;
ev.events = events;
- // std::map's iterators do not get invalidated until erased, so we use the
- // pointer to the std::function in the map directly for epoll_ctl.
- ev.data.ptr = reinterpret_cast<void*>(&it->second);
+ ev.data.fd = fd;
if (epoll_ctl(epoll_fd_, EPOLL_CTL_ADD, fd, &ev) == -1) {
Result<void> result = ErrnoError() << "epoll_ctl failed to add fd";
epoll_handlers_.erase(fd);
@@ -96,7 +94,11 @@
}
std::vector<std::shared_ptr<Handler>> pending_functions;
for (int i = 0; i < num_events; ++i) {
- auto& info = *reinterpret_cast<Info*>(ev[i].data.ptr);
+ const auto it = epoll_handlers_.find(ev[i].data.fd);
+ if (it == epoll_handlers_.end()) {
+ continue;
+ }
+ const Info& info = it->second;
if ((info.events & (EPOLLIN | EPOLLPRI)) == (EPOLLIN | EPOLLPRI) &&
(ev[i].events & EPOLLIN) != ev[i].events) {
// This handler wants to know about exception events, and just got one.