[Qemu-commits] [qemu/qemu] f56281: block/qcow2-bitmap: fix crash bug in qcow2_co_remo...

[Peter Maydell]

  Branch: refs/heads/master
  Home:   https://github.com/qemu/qemu
  Commit: f56281abd957561b30538cbe606c3793b9b4c56d
      
https://github.com/qemu/qemu/commit/f56281abd957561b30538cbe606c3793b9b4c56d
  Author: Vladimir Sementsov-Ogievskiy <address@hidden>
  Date:   2019-12-09 (Mon, 09 Dec 2019)

  Changed paths:
    M block/qcow2-bitmap.c

  Log Message:
  -----------
  block/qcow2-bitmap: fix crash bug in qcow2_co_remove_persistent_dirty_bitmap

Here is double bug:

First, return error but not set errp. This may lead to:
qmp block-dirty-bitmap-remove may report success when actually failed

block-dirty-bitmap-remove used in a transaction will crash, as
qmp_transaction will think that it returned success and will call
block_dirty_bitmap_remove_commit which will crash, as state->bitmap is
NULL

Second (like in anecdote), this case is not an error at all. As it is
documented in the comment above bdrv_co_remove_persistent_dirty_bitmap
definition, absence of bitmap is not an error, and similar case handled
at start of qcow2_co_remove_persistent_dirty_bitmap, it returns 0 when
there is no bitmaps at all.

But when there are some bitmaps, but not the requested one, it return
error with errp unset.

Fix that.

Trigger:
1. create persistent bitmap A
2. shutdown vm  (bitmap A is synced)
3. start vm
4. create persistent bitmap B
5. remove bitmap B - it fails (and crashes if in transaction)

Potential workaround (rather invasive to ask clients to implement it):
1. create persistent bitmap A
2. shutdown vm
3. start vm
4. create persistent bitmap B
5. remember, that we want to remove bitmap B after vm shutdown
...
  some other operations
...
6. vm shutdown
7. start vm in stopped mode, and remove all bitmaps marked for removing
8. stop vm

Fixes: b56a1e31759b750
Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
Message-Id: <address@hidden>
Reviewed-by: Eric Blake <address@hidden>
Reviewed-by: John Snow <address@hidden>
[eblake: commit message tweaks]
Signed-off-by: Eric Blake <address@hidden>


  Commit: 9b4efa2ede5db24377405a21b218066b90fe2f0e
      
https://github.com/qemu/qemu/commit/9b4efa2ede5db24377405a21b218066b90fe2f0e
  Author: Peter Maydell <address@hidden>
  Date:   2019-12-09 (Mon, 09 Dec 2019)

  Changed paths:
    M block/qcow2-bitmap.c

  Log Message:
  -----------
  Merge remote-tracking branch 'remotes/ericb/tags/pull-nbd-2019-12-09' into 
staging

bitmap fix for 4.2-rc5

- Fix a regression that broke bitmap deletion without a transaction,
and causes a crash with transaction (only transaction is new to 4.2),
when a qcow2 file contains persistent bitmaps from prior shutdown

# gpg: Signature made Mon 09 Dec 2019 15:28:19 GMT
# gpg:                using RSA key 71C2CC22B1C4602927D2F3AAA7A16B4A2527436A
# gpg: Good signature from "Eric Blake <address@hidden>" [full]
# gpg:                 aka "Eric Blake (Free Software Programmer) 
<address@hidden>" [full]
# gpg:                 aka "[jpeg image of size 6874]" [full]
# Primary key fingerprint: 71C2 CC22 B1C4 6029 27D2  F3AA A7A1 6B4A 2527 436A

* remotes/ericb/tags/pull-nbd-2019-12-09:
  block/qcow2-bitmap: fix crash bug in qcow2_co_remove_persistent_dirty_bitmap

Signed-off-by: Peter Maydell <address@hidden>


Compare: https://github.com/qemu/qemu/compare/8350b17be015...9b4efa2ede5d