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Commit b0177a08 authored by Bart Van Assche's avatar Bart Van Assche
Browse files

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: default avatarBart Van Assche <bvanassche@google.com>
parent 9457a9ab

init/epoll.cpp

+6 −4
Original line number Diff line number Diff line
@@ -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.