** Also affects: python-apt (Ubuntu Xenial)
Importance: Undecided
Status: New
** Also affects: update-manager (Ubuntu Xenial)
Importance: Undecided
Status: New
** Also affects: python-apt (Ubuntu Trusty)
Importance: Undecided
Status: New
** Also affects: update-manager (Ubuntu Trusty)
Importance: Undecided
Status: New
** Description changed:
+ ========== xenial / trusty ==========
+ [Impact]
+ Some applications, like unattended-upgrades or update-manager, reopen the apt
cache. They also keep around old apt.Package objects however, and operate on
them after reopening. Under the hood, this means that apt_pkg.Package objects
belonging to an old cache are passed to a new cache.
+
+ APT relies on the ID of the package (it's position in the cache) for
+ it's operation. So if a package has ID 0 in the old cache, and a
+ different package has ID 0 in the new cache, performing operations on
+ the old package would perform it on the new package. If the old
+ package's ID is out of bounds in the new cache, the behavior is
+ undefined - it's an out of bounds array access.
+
+ [Test case]
+ The attached test case has a list of packages 0-9, a-z; stores the package
"z" into a variable, then reopens the cache. It then marks z for deletion. This
either segfaults or does nothing; when it should mark z for deletion.
+
+ More test cases like this are in the autopkgtest.
+
+ [Regression potential]
+ The initial fix introduced bug 1780099, there might be similar bugs lurking.
However, these bugs would have been undefined behavior before and might have
caused segmentation faults or did the wrong thing. It seems likely that any
regression cannot possibly be worse than the current state.
+
+ ========== bionic+ ===================
+
[Impact]
python-apt 1.6 raises an exception when objects of an old cache are passed to
a apt_pkg.DepCache methods for a different cache. Prior to that, those would
either segfault, succeed, or silently operate on a different object, as they
use package/version ids, and e.g. two different packages in the old and new
cache might have the same id.
With 1.6.1, we introduce a remapping algorithm that remaps objects of
apt.Cache() when calling apt.Cache.open(), allowing old objects to be
used after reopening, as long as they exist in the new cache. If they
don't exist in the new cache, apt_pkg.CacheMismatchError will be raised
from the apt_pkg layer.
[Test case]
import apt
c=apt.Cache()
p=c["apt"]
c.open()
p.mark_install()
[Regression potential]
Could be remapping to wrong items which would cause us to install a wrong
version, for example. Compared to pre-bionic, bionic is a regression already,
though, and any regression caused here is less important than
what we have now.
[Original bug report]
The Ubuntu Error Tracker has been receiving reports about a problem regarding
update-manager. This problem was most recently seen with package version
1:18.04.11, the problem page at
https://errors.ubuntu.com/problem/e6ff7b5c385c512b7933497ad895c8a19ed063b2
contains more details, including versions of packages affected, stacktrace or
traceback, and individual crash reports.
If you do not have access to the Ubuntu Error Tracker and are a software
developer, you can request it at http://forms.canonical.com/reports/.
** Attachment added: "Test case for xenial/trusty"
https://bugs.launchpad.net/ubuntu/+source/update-manager/+bug/1773316/+attachment/5159649/+files/a.py
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https://bugs.launchpad.net/bugs/1773316
Title:
Object of different cache passed as argument to apt_pkg.DepCache
method
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