diff options
| author | Jens Axboe <axboe@kernel.dk> | 2020-02-02 18:23:03 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2020-02-11 15:34:08 +0300 |
| commit | eaef83c4c0cb8c82ab7cea99479d49d35a5cd25d (patch) | |
| tree | 4f5837096454967295249bde5c311130ac6a4865 /fs/eventfd.c | |
| parent | e608cd92bac3a37436666b75e7272af968ebbbc5 (diff) | |
| download | linux-eaef83c4c0cb8c82ab7cea99479d49d35a5cd25d.tar.xz | |
eventfd: track eventfd_signal() recursion depth
commit b5e683d5cab8cd433b06ae178621f083cabd4f63 upstream.
eventfd use cases from aio and io_uring can deadlock due to circular
or resursive calling, when eventfd_signal() tries to grab the waitqueue
lock. On top of that, it's also possible to construct notification
chains that are deep enough that we could blow the stack.
Add a percpu counter that tracks the percpu recursion depth, warn if we
exceed it. The counter is also exposed so that users of eventfd_signal()
can do the right thing if it's non-zero in the context where it is
called.
Cc: stable@vger.kernel.org # 4.19+
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'fs/eventfd.c')
| -rw-r--r-- | fs/eventfd.c | 15 |
1 files changed, 15 insertions, 0 deletions
diff --git a/fs/eventfd.c b/fs/eventfd.c index 08d3bd602f73..ce1d1711fbba 100644 --- a/fs/eventfd.c +++ b/fs/eventfd.c @@ -22,6 +22,8 @@ #include <linux/proc_fs.h> #include <linux/seq_file.h> +DEFINE_PER_CPU(int, eventfd_wake_count); + struct eventfd_ctx { struct kref kref; wait_queue_head_t wqh; @@ -55,12 +57,25 @@ __u64 eventfd_signal(struct eventfd_ctx *ctx, __u64 n) { unsigned long flags; + /* + * Deadlock or stack overflow issues can happen if we recurse here + * through waitqueue wakeup handlers. If the caller users potentially + * nested waitqueues with custom wakeup handlers, then it should + * check eventfd_signal_count() before calling this function. If + * it returns true, the eventfd_signal() call should be deferred to a + * safe context. + */ + if (WARN_ON_ONCE(this_cpu_read(eventfd_wake_count))) + return 0; + spin_lock_irqsave(&ctx->wqh.lock, flags); + this_cpu_inc(eventfd_wake_count); if (ULLONG_MAX - ctx->count < n) n = ULLONG_MAX - ctx->count; ctx->count += n; if (waitqueue_active(&ctx->wqh)) wake_up_locked_poll(&ctx->wqh, EPOLLIN); + this_cpu_dec(eventfd_wake_count); spin_unlock_irqrestore(&ctx->wqh.lock, flags); return n; |