[pve-devel] [PATCH] qemu 2.0.0: has a use after free bug in aio completion resulting in segfaults

[Stefan Priebe]

details in 0001-aio-Fix-use-after-free-in-cancellation-path.patch
---
 ...o-Fix-use-after-free-in-cancellation-path.patch |   75 ++++++++++++++++++++
 debian/patches/series                              |    1 +
 2 files changed, 76 insertions(+)
 create mode 100644 debian/patches/0001-aio-Fix-use-after-free-in-cancellation-path.patch

diff --git a/debian/patches/0001-aio-Fix-use-after-free-in-cancellation-path.patch b/debian/patches/0001-aio-Fix-use-after-free-in-cancellation-path.patch
new file mode 100644
index 0000000..df88f44
--- /dev/null
+++ b/debian/patches/0001-aio-Fix-use-after-free-in-cancellation-path.patch
@@ -0,0 +1,75 @@
+From 271c0f68b4eae72691721243a1c37f46a3232d61 Mon Sep 17 00:00:00 2001
+From: Fam Zheng <famz at redhat.com>
+Date: Wed, 21 May 2014 10:42:13 +0800
+Subject: [PATCH] aio: Fix use-after-free in cancellation path
+
+The current flow of canceling a thread from THREAD_ACTIVE state is:
+
+  1) Caller wants to cancel a request, so it calls thread_pool_cancel.
+
+  2) thread_pool_cancel waits on the conditional variable
+     elem->check_cancel.
+
+  3) The worker thread changes state to THREAD_DONE once the task is
+     done, and notifies elem->check_cancel to allow thread_pool_cancel
+     to continue execution, and signals the notifier (pool->notifier) to
+     allow callback function to be called later. But because of the
+     global mutex, the notifier won't get processed until step 4) and 5)
+     are done.
+
+  4) thread_pool_cancel continues, leaving the notifier signaled, it
+     just returns to caller.
+
+  5) Caller thinks the request is already canceled successfully, so it
+     releases any related data, such as freeing elem->common.opaque.
+
+  6) In the next main loop iteration, the notifier handler,
+     event_notifier_ready, is called. It finds the canceled thread in
+     THREAD_DONE state, so calls elem->common.cb, with an (likely)
+     dangling opaque pointer. This is a use-after-free.
+
+Fix it by calling event_notifier_ready before leaving
+thread_pool_cancel.
+
+Test case update: This change will let cancel complete earlier than
+test-thread-pool.c expects, so update the code to check this case: if
+it's already done, done_cb sets .aiocb to NULL, skip calling
+bdrv_aio_cancel on them.
+
+Reported-by: Ulrich Obergfell <uobergfe at redhat.com>
+Suggested-by: Paolo Bonzini <pbonzini at redhat.com>
+Signed-off-by: Fam Zheng <famz at redhat.com>
+Signed-off-by: Stefan Hajnoczi <stefanha at redhat.com>
+---
+ tests/test-thread-pool.c |    2 +-
+ thread-pool.c            |    1 +
+ 2 files changed, 2 insertions(+), 1 deletion(-)
+
+diff --git a/tests/test-thread-pool.c b/tests/test-thread-pool.c
+index c1f8e13..aa156bc 100644
+--- a/tests/test-thread-pool.c
++++ b/tests/test-thread-pool.c
+@@ -180,7 +180,7 @@ static void test_cancel(void)
+ 
+     /* Canceling the others will be a blocking operation.  */
+     for (i = 0; i < 100; i++) {
+-        if (data[i].n != 3) {
++        if (data[i].aiocb && data[i].n != 3) {
+             bdrv_aio_cancel(data[i].aiocb);
+         }
+     }
+diff --git a/thread-pool.c b/thread-pool.c
+index fbdd3ff..dfb699d 100644
+--- a/thread-pool.c
++++ b/thread-pool.c
+@@ -224,6 +224,7 @@ static void thread_pool_cancel(BlockDriverAIOCB *acb)
+         pool->pending_cancellations--;
+     }
+     qemu_mutex_unlock(&pool->lock);
++    event_notifier_ready(&pool->notifier);
+ }
+ 
+ static const AIOCBInfo thread_pool_aiocb_info = {
+-- 
+1.7.10.4
+
diff --git a/debian/patches/series b/debian/patches/series
index a7609e9..3dc1c11 100644
--- a/debian/patches/series
+++ b/debian/patches/series
@@ -25,3 +25,4 @@ backup-vma-remove-async-queue.patch
 internal-snapshot-async.patch
 disable-efi-enable-pxe-roms.patch
 backup-vma-allow-empty-backups.patch
+0001-aio-Fix-use-after-free-in-cancellation-path.patch
-- 
1.7.10.4