thebeanogamer / rpms / qemu-kvm

Forked from rpms/qemu-kvm 5 months ago
Clone
Blob Blame History Raw
From 0fd571f772eb449da398b029705f4cadf0129f60 Mon Sep 17 00:00:00 2001
From: Kevin Wolf <kwolf@redhat.com>
Date: Wed, 10 Oct 2018 20:22:04 +0100
Subject: [PATCH 38/49] block-backend: Fix potential double blk_delete()
RH-Author: Kevin Wolf <kwolf@redhat.com>
Message-id: <20181010202213.7372-26-kwolf@redhat.com>
Patchwork-id: 82615
O-Subject: [RHEL-8 qemu-kvm PATCH 35/44] block-backend: Fix potential double blk_delete()
Bugzilla: 1637976
RH-Acked-by: Max Reitz <mreitz@redhat.com>
RH-Acked-by: John Snow <jsnow@redhat.com>
RH-Acked-by: Thomas Huth <thuth@redhat.com>
blk_unref() first decreases the refcount of the BlockBackend and calls
blk_delete() if the refcount reaches zero. Requests can still be in
flight at this point, they are only drained during blk_delete():
At this point, arbitrary callbacks can run. If any callback takes a
temporary BlockBackend reference, it will first increase the refcount to
1 and then decrease it to 0 again, triggering another blk_delete(). This
will cause a use-after-free crash in the outer blk_delete().
Fix it by draining the BlockBackend before decreasing to refcount to 0.
Assert in blk_ref() that it never takes the first refcount (which would
mean that the BlockBackend is already being deleted).
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
(cherry picked from commit 5ca9d21bd1c8eeb578d0964e31bd03d47c25773d)
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Danilo C. L. de Paula <ddepaula@redhat.com>
---
block/block-backend.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/block/block-backend.c b/block/block-backend.c
index dffc6f0..bfd0331 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -436,6 +436,7 @@ int blk_get_refcnt(BlockBackend *blk)
*/
void blk_ref(BlockBackend *blk)
{
+ assert(blk->refcnt > 0);
blk->refcnt++;
}
@@ -448,7 +449,13 @@ void blk_unref(BlockBackend *blk)
{
if (blk) {
assert(blk->refcnt > 0);
- if (!--blk->refcnt) {
+ if (blk->refcnt > 1) {
+ blk->refcnt--;
+ } else {
+ blk_drain(blk);
+ /* blk_drain() cannot resurrect blk, nobody held a reference */
+ assert(blk->refcnt == 1);
+ blk->refcnt = 0;
blk_delete(blk);
}
}
--
1.8.3.1