[pve-devel] [PATCH v2 qemu 1/2] replicated zfs migration: fix assertion failure with multiple disks

[Fiona Ebner]

It is necessary to reset the error pointer after error_report_err(),
because that function frees the error. Not doing so can lead to a
use-after-free and in particular error_setg() with the same error
pointer will run into assertion failure, because it asserts that no
previous error is set:

> #5  0x00007c1723674eb2 in __GI___assert_fail (assertion=assertion at entry=0x59132c9fc540 "*errp == NULL",
>     file=file at entry=0x59132c9fc530 "../util/error.c", line=line at entry=68,
>     function=function at entry=0x59132c9fc5f8 <__PRETTY_FUNCTION__.2> "error_setv")
> #6  0x000059132c7d250f in error_setv (errp=0x7c15839fafb8, src=0x59132c9af224 "../block/dirty-bitmap.c", line=182,
>     func=0x59132c9af9b0 <__func__.17> "bdrv_dirty_bitmap_check", err_class=err_class at entry=ERROR_CLASS_GENERIC_ERROR,
>     fmt=fmt at entry=0x59132c9af380 "Bitmap '%s' is currently in use by another operation and cannot be used", ap=0x7c15839fad60,
>     suffix=0x0)
> #7  0x000059132c7d265c in error_setg_internal (errp=errp at entry=0x7c15839fafb8,
>     src=src at entry=0x59132c9af224 "../block/dirty-bitmap.c", line=line at entry=182,
>     func=func at entry=0x59132c9af9b0 <__func__.17> "bdrv_dirty_bitmap_check",
>     fmt=fmt at entry=0x59132c9af380 "Bitmap '%s' is currently in use by another operation and cannot be used")
> #8  0x000059132c68fbc1 in bdrv_dirty_bitmap_check (bitmap=bitmap at entry=0x5913542d6190, flags=flags at entry=7,
>     errp=errp at entry=0x7c15839fafb8)
> #9  0x000059132c3b951d in add_bitmaps_to_list (s=s at entry=0x59132d87ee40 <dbm_state>, bs=bs at entry=0x591352d6b720,
>     bs_name=bs_name at entry=0x591352d69900 "drive-scsi1", alias_map=alias_map at entry=0x0, errp=errp at entry=0x7c15839fafb8)
> #10 0x000059132c3ba23d in init_dirty_bitmap_migration (errp=<optimized out>, s=0x59132d87ee40 <dbm_state>)
> #11 dirty_bitmap_save_setup (f=0x591352ebdd30, opaque=0x59132d87ee40 <dbm_state>, errp=0x7c15839fafb8)
> #12 0x000059132c3d81f0 in qemu_savevm_state_setup (f=0x591352ebdd30, errp=errp at entry=0x7c15839fafb8)

Fix created using the appropriate in-tree coccinelle script:
spatch --in-place scripts/coccinelle/error-use-after-free.cocci migration/block-dirty-bitmap.c

The problematic change exposing the issue was part of 7882afe ("update
submodule and patches to QEMU 9.1.2") adapting to QEMU 9.1, commit
dd03167725 ("migration: Add Error** argument to
add_bitmaps_to_list()"), where the add_bitmaps_to_list() function
gained an error pointer argument, replacing the local error variable
that was used before.

Fixes: 7882afe ("update submodule and patches to QEMU 9.1.2")
Signed-off-by: Fiona Ebner <f.ebner at proxmox.com>
---

No changes in v2.

 ...tion-block-dirty-bitmap-migrate-other-bitmaps-e.patch | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/debian/patches/pve/0035-migration-block-dirty-bitmap-migrate-other-bitmaps-e.patch b/debian/patches/pve/0035-migration-block-dirty-bitmap-migrate-other-bitmaps-e.patch
index 066ad77..364824d 100644
--- a/debian/patches/pve/0035-migration-block-dirty-bitmap-migrate-other-bitmaps-e.patch
+++ b/debian/patches/pve/0035-migration-block-dirty-bitmap-migrate-other-bitmaps-e.patch
@@ -15,20 +15,21 @@ transferred.
 Signed-off-by: Stefan Reiter <s.reiter at proxmox.com>
 Signed-off-by: Thomas Lamprecht <t.lamprecht at proxmox.com>
 ---
- migration/block-dirty-bitmap.c | 5 ++++-
- 1 file changed, 4 insertions(+), 1 deletion(-)
+ migration/block-dirty-bitmap.c | 6 +++++-
+ 1 file changed, 5 insertions(+), 1 deletion(-)
 
 diff --git a/migration/block-dirty-bitmap.c b/migration/block-dirty-bitmap.c
-index a7d55048c2..77346a5fa2 100644
+index a7d55048c2..44078ea670 100644
 --- a/migration/block-dirty-bitmap.c
 +++ b/migration/block-dirty-bitmap.c
-@@ -539,7 +539,10 @@ static int add_bitmaps_to_list(DBMSaveState *s, BlockDriverState *bs,
+@@ -539,7 +539,11 @@ static int add_bitmaps_to_list(DBMSaveState *s, BlockDriverState *bs,
          }
  
          if (bdrv_dirty_bitmap_check(bitmap, BDRV_BITMAP_DEFAULT, errp)) {
 -            return -1;
 +            if (errp != NULL) {
 +                error_report_err(*errp);
++                *errp = NULL;
 +            }
 +            continue;
          }
-- 
2.39.5