[kontact] [Bug 412461] New: Crash or extreme memory usage (over 20 gigabytes, OOM) on large attachment, over a gigabyte

[Melvin Vermeeren]

https://bugs.kde.org/show_bug.cgi?id=412461

            Bug ID: 412461
           Summary: Crash or extreme memory usage (over 20 gigabytes, OOM)
                    on large attachment, over a gigabyte
           Product: kontact
           Version: 5.9.2
          Platform: Debian stable
                OS: Linux
            Status: REPORTED
          Severity: major
          Priority: NOR
         Component: mail
          Assignee: kdepim-bugs at kde.org
          Reporter: mail at mel.vin
  Target Milestone: ---

Created attachment 122939
  --> https://bugs.kde.org/attachment.cgi?id=122939&action=edit
htop prior to freeze and OOM

(Note: perhaps this bug should be filed under akonadi and kmail too.)

These are really two distinct bugs, both related to absurdly large attachments.

1. When attaching a really large attachment (try one of a few GB), Kontact
crashes. This one is not so bad, you restart Kontact and it still works.

2. When attaching a large-but-not-large-enough-to-crash attachment (a 779,5 MiB
file), it gets accepted but akonadi then completely chokes and uses 20GB+ RAM
spread over its agents until kernel OOM killer nukes it. The message is stuck
in outbox, any access to local folders will trigger message processing again
leading to the 20GB+ RAM usage again.

STEPS TO REPRODUCE
1. Attach a 779,5 MiB attachment to a mail in the composer.
2. Attempt to send the mail.

OBSERVED RESULT

The mail gets stuck in the local folders outbox and OOM will quickly follow.
(Unless you have enough RAM, perhaps 100GB or so?) Every access of local
folders will cause akonadi to re-read this mail, because it's stuck in the
outbox, triggering the issue again and again.

EXPECTED RESULT

One of:
a. It works without crashing or consuming a ridiculous amount of memory.
b. It refuses to attach ridiculously oversized attachments.

WORKAROUND

If a mail with an extremely large attachment is stuck in the local folders, use
"ncdu" or similar tool to locate the mail file on disk. For example "ncdu
~/.local/share/akonadi_maildir_resource_0".

Then, stop akonadi, delete the problematic file and start akonadi again.

RECOMMENDED FIX

Set the composer setting "Maximum Attachment Size" somewhere between 50MB and
100MB or so by default. Then also either disallow unlimited attachment size
completely or add a gigantic warning regarding the memory usage if set to
unlimited.

SOFTWARE/OS VERSIONS
Kontact 5.9.3 (18.08.3, Debian Buster/Stable)
Operating System: Debian GNU/Linux 10
KDE Plasma Version: 5.14.5
Qt Version: 5.11.3
KDE Frameworks Version: 5.54.0
Kernel Version: 4.19.0-6-amd64
OS Type: 64-bit

ADDITIONAL INFORMATION

See the attachment for htop output just before system unresponsiveness due to
swapping and OOM killer invocation.

Personal note: Although it may seem silly trying to try and attach a gigantic
file to an email, I've seen this bug in production. Dragging & dropping a large
LibreOffice presentation from Dolphin into Kontact is easily done, and the
user's Kontact/akonadi is completely crippled afterwards if the file size
happens to be in the "sweet spot".

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