68 lines
2.3 KiB
Diff
68 lines
2.3 KiB
Diff
From 21a2ef76c6aa33f0058d149b1bfdde1d27ba1df4 Mon Sep 17 00:00:00 2001
|
|
From: Kevin Wolf <kwolf@redhat.com>
|
|
Date: Wed, 10 Oct 2018 20:22:04 +0100
|
|
Subject: 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 2b837d1..94046f0 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
|
|
|