Hi Shoily,
Coming back around to this issue, it looks like
b431ef837e3374da0db8ff6683170359aaa0859c landed in focal in 5.4.0-49.53
and bionic in 4.15.0-119.120. I'm making this public as well as marking
it as fix released.
Thanks again for the report!
** Information type changed from Private Security to Public
** Changed in: linux (Ubuntu)
Status: New => Fix Released
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https://bugs.launchpad.net/bugs/1904471
Title:
Ubuntu-5.4.0-48.52 introduces a regression by cherry picking partial
fixes from set of commits
Status in linux package in Ubuntu:
Fix Released
Bug description:
Hello,
While I was porting a security fix pertaining to blktrace and debugfs,
I have noticed that ubuntu-5.4.0-48.52 kernel is missing fix
b431ef837e3374da0db8ff6683170359aaa0859c from mainline kernel.
Here ubuntu-5.4.0-48.52 picked partial fixes from set of commits which
is solves a race condition present in blktrace and debugfs. This is
explained by the Kernel developer Luis Chamberlain <[email protected]>
in the thread https://bugzilla.kernel.org/show_bug.cgi?id=205713 -
The fixes for this is now queued up on the block for-next branch, on
its way for v5.9. There were quite a bit of scattered fixes required
for this, if you are looking to backport this to your kernel be sure
to include starting from "blktrace: break out of blktrace setup on
concurrent calls" up to "blktrace: ensure our debugfs dir exists". The
actual fix for this particular crash however is handled by the patch
titled, "blktrace: fix debugfs use after free"
Commit 4a6f7d09462878b26c4732c8fa0c7e7d22ac1564 in ubuntu-5.4.0-48.52
caused the regression by removing NULL check for debugfs dir. This is
fixed in mainline kernel commit
b431ef837e3374da0db8ff6683170359aaa0859c which is missing in ubuntu.
Let me know if you have further question.
Thanks,
Shoily Rahman
[email protected]
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