Messages in this thread | | | Date | Tue, 16 Jun 2015 13:27:05 -0700 (PDT) | From | Hugh Dickins <> | Subject | Re: mm: shmem_zero_setup skip security check and lockdep conflict with XFS |
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On Mon, 15 Jun 2015, Daniel Wagner wrote: > On 06/14/2015 06:48 PM, Hugh Dickins wrote: > > It appears that, at some point last year, XFS made directory handling > > changes which bring it into lockdep conflict with shmem_zero_setup(): > > it is surprising that mmap() can clone an inode while holding mmap_sem, > > but that has been so for many years. > > > > Since those few lockdep traces that I've seen all implicated selinux, > > I'm hoping that we can use the __shmem_file_setup(,,,S_PRIVATE) which > > v3.13's commit c7277090927a ("security: shmem: implement kernel private > > shmem inodes") introduced to avoid LSM checks on kernel-internal inodes: > > the mmap("/dev/zero") cloned inode is indeed a kernel-internal detail. > > > > This also covers the !CONFIG_SHMEM use of ramfs to support /dev/zero > > (and MAP_SHARED|MAP_ANONYMOUS). I thought there were also drivers > > which cloned inode in mmap(), but if so, I cannot locate them now. > > > > Reported-and-tested-by: Prarit Bhargava <prarit@redhat.com> > > Reported-by: Daniel Wagner <wagi@monom.org> > > Reported-and-tested-by: Daniel Wagner <wagi@monom.org>
Great, thank you Daniel: we look more convincing now :)
> > Sorry for the long delay. It took me a while to figure out my original > setup. I could verify that this patch made the lockdep message go away > on 4.0-rc6 and also on 4.1-rc8.
Thank you for taking the trouble.
> > For the record: SELinux needs to be enabled triggering it.
Right, selinux was in all the stacktraces we saw, and I was banking on that security "recursion" being what actually upset lockdep; but couldn't be sure until you tried it out.
We didn't make -rc8, and I won't be at all surprised if Linus feels that a year(?)-old lockdep warning is not worth disturbing v4.1 final for, but it should get into v4.2 (thank you, Andrew).
Hugh
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