| 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 |
| |
| |
| @@ -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 |
| |