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init/epoll: Fix a potential use-after-free

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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>
This commit is contained in:
Bart Van Assche 2022-10-18 15:48:31 -07:00
parent 9457a9ab72
commit b0177a0828
1 changed files with 6 additions and 4 deletions
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10
init/epoll.cpp
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@ -54,9 +54,7 @@ Result<void> Epoll::RegisterHandler(int fd, Handler handler, uint32_t events) {
}
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 @@ Result<std::vector<std::shared_ptr<Epoll::Handler>>> Epoll::Wait(
}
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.