aio-posix: fix use after leaving scope in aio_poll()

epoll_handler is a stack variable and must not be accessed after it goes
out of scope:

      if (aio_epoll_check_poll(ctx, pollfds, npfd, timeout)) {
          AioHandler epoll_handler;
          ...
          add_pollfd(&epoll_handler);
          ret = aio_epoll(ctx, pollfds, npfd, timeout);
      } ...

  ...

  /* if we have any readable fds, dispatch event */
  if (ret > 0) {
      for (i = 0; i < npfd; i++) {
          nodes[i]->pfd.revents = pollfds[i].revents;
      }
  }

nodes[0] is &epoll_handler, which has already gone out of scope.

There is no need to use pollfds[] for epoll.  We don't need an
AioHandler for the epoll fd.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Sergio Lopez <slp@redhat.com>
Message-id: 20200214171712.541358-2-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

1 files changed, 8 insertions, 12 deletions

diff --git a/util/aio-posix.c b/util/aio-posix.c
index f67f5b34e9..c964627a03 100644
--- a/util/aio-posix.c
+++ b/util/aio-posix.c
@@ -105,17 +105,18 @@ static void aio_epoll_update(AioContext *ctx, AioHandler *node, bool is_new)
     }
 }
 
-static int aio_epoll(AioContext *ctx, GPollFD *pfds,
-                     unsigned npfd, int64_t timeout)
+static int aio_epoll(AioContext *ctx, int64_t timeout)
 {
+    GPollFD pfd = {
+        .fd = ctx->epollfd,
+        .events = G_IO_IN | G_IO_OUT | G_IO_HUP | G_IO_ERR,
+    };
     AioHandler *node;
     int i, ret = 0;
     struct epoll_event events[128];
 
-    assert(npfd == 1);
-    assert(pfds[0].fd == ctx->epollfd);
     if (timeout > 0) {
-        ret = qemu_poll_ns(pfds, npfd, timeout);
+        ret = qemu_poll_ns(&pfd, 1, timeout);
     }
     if (timeout <= 0 || ret > 0) {
         ret = epoll_wait(ctx->epollfd, events,
@@ -669,13 +670,8 @@ bool aio_poll(AioContext *ctx, bool blocking)
 
         /* wait until next event */
         if (aio_epoll_check_poll(ctx, pollfds, npfd, timeout)) {
-            AioHandler epoll_handler;
-
-            epoll_handler.pfd.fd = ctx->epollfd;
-            epoll_handler.pfd.events = G_IO_IN | G_IO_OUT | G_IO_HUP | G_IO_ERR;
-            npfd = 0;
-            add_pollfd(&epoll_handler);
-            ret = aio_epoll(ctx, pollfds, npfd, timeout);
+            npfd = 0; /* pollfds[] is not being used */
+            ret = aio_epoll(ctx, timeout);
         } else  {
             ret = qemu_poll_ns(pollfds, npfd, timeout);
         }