[SRU][J/I/H/F][PATCH 0/1] Drop "UBUNTU: SAUCE: cachefiles: Page leaking in cachefiles_read_backing_file while vmscan is active"

[Andrea Righi]

On Tue, Oct 19, 2021 at 09:02:44AM -0300, Thadeu Lima de Souza Cascardo wrote:
> On Tue, Oct 19, 2021 at 12:33:07PM +0200, Andrea Righi wrote:
> > BugLink: https://bugs.launchpad.net/bugs/1947709
> > 
> > [Impact]
> > 
> > "UBUNTU: SAUCE: cachefiles: Page leaking in cachefiles_read_backing_file while
> > vmscan is active" has been applied to fix a page leaking issue.
> > 
> > However a slightly different fix has been applied upstream:
> > 
> >  9a24ce5b66f9 ("cachefiles: Fix page leak in cachefiles_read_backing_file while vmscan is active")
> > 
> > Basically we are fixing the same issue in two different ways at the same time,
> > but even worse our patch an introduce a potential NULL pointer dereference: we
> > do a put_page(newpage) and set newpage = NULL in the main for() loop and then
> > we may do additional put_page(newpage) after the main for loop if
> > ret == -EEXIST, that would trigger the NULL pointer dereference.
> > 
> 
> So, I see bionic has the SAUCE patch, but does not have the upstream one. We
> should revert the SAUCE patch on bionic as well and apply the upstream patch
> there.

Agreed. I can send another SRU email to include bionic as well.

> 
> Also, the upstream commit has a test case, are you able to use it?
> 
> Thanks.
> Cascardo.

I haven't tried the test case yet, because it requires to setup an NFS
server, I'll do some tests later today to see if I can trigger any bug.

Thanks,
-Andrea