On 10/14/19 6:35 PM, William Brown wrote:
On 15 Oct 2019, at 06:58, Mark Reynolds <mreyno...@redhat.com> wrote:
So we are finding these race conditions (leading to heap-use-after-free) when
you stop the server while an import task is running. The current code aborts
the task which leaves the database unusable until it is fully reinitialized at
a later time. Unfortunately the code that handles this is complex, and very
error prone.
I'd like to allow the import task to complete before fully shutting the server
down. Code fix is trivial, but do we want the import to finish, or should the
import be aborted (and database left broken)? Thoughts? Opinions?
The question is "what does the admin expect"? I could envisage if you start an
import and then cancel the task, you expect:
* The task to be immediately stopped
* The db content rolled back.
Shouldn't we be in a betxn or similar during an import so we can revert?
Failing this, I'd assume the user would expect a ctrl-c to immediately cancel
the task.
What kind of use-after-frees are we seeing?
See
https://pagure.io/389-ds-base/issue/50646
Pretty sure the first thing the import does is delete the db directory, but I have not
found that in the code yet, but there are definitely no transactions used during an
"import". It's a very different process. Now rolling back the database would
be nice, but I can imagine very large databases(100+ million entries) where disk space
could be an issue if you have to keep the old database around until the new one is
imported.
As for aborting, currently there is no abort mechanism except for stopping the
server. So a ctrl-C is not really an option at this time. Keep in mind I can
still easily keep the current abort behavior during a shutdown, but in the
current design if you abort an import the database is hosed.
Thanks,
Mark
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—
Sincerely,
William Brown
Senior Software Engineer, 389 Directory Server
SUSE Labs
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