[PATCH v3] nfsd: set security label during create operations

[Stephen Smalley]

On Thu, May 16, 2024 at 1:29 PM Stephen Smalley
<stephen.smalley.work at gmail.com> wrote:
>
> On Wed, May 15, 2024 at 10:52 AM Stephen Smalley
> <stephen.smalley.work at gmail.com> wrote:
> >
> > On Mon, May 6, 2024 at 1:46 AM NeilBrown <neilb at suse.de> wrote:
> > >
> > > On Fri, 03 May 2024, Stephen Smalley wrote:
> > > > When security labeling is enabled, the client can pass a file security
> > > > label as part of a create operation for the new file, similar to mode
> > > > and other attributes. At present, the security label is received by nfsd
> > > > and passed down to nfsd_create_setattr(), but nfsd_setattr() is never
> > > > called and therefore the label is never set on the new file. This bug
> > > > may have been introduced on or around commit d6a97d3f589a ("NFSD:
> > > > add security label to struct nfsd_attrs"). Looking at nfsd_setattr()
> > > > I am uncertain as to whether the same issue presents for
> > > > file ACLs and therefore requires a similar fix for those.
> > > >
> > > > An alternative approach would be to introduce a new LSM hook to set the
> > > > "create SID" of the current task prior to the actual file creation, which
> > > > would atomically label the new inode at creation time. This would be better
> > > > for SELinux and a similar approach has been used previously
> > > > (see security_dentry_create_files_as) but perhaps not usable by other LSMs.
> > > >
> > > > Reproducer:
> > > > 1. Install a Linux distro with SELinux - Fedora is easiest
> > > > 2. git clone https://github.com/SELinuxProject/selinux-testsuite
> > > > 3. Install the requisite dependencies per selinux-testsuite/README.md
> > > > 4. Run something like the following script:
> > > > MOUNT=$HOME/selinux-testsuite
> > > > sudo systemctl start nfs-server
> > > > sudo exportfs -o rw,no_root_squash,security_label localhost:$MOUNT
> > > > sudo mkdir -p /mnt/selinux-testsuite
> > > > sudo mount -t nfs -o vers=4.2 localhost:$MOUNT /mnt/selinux-testsuite
> > > > pushd /mnt/selinux-testsuite/
> > > > sudo make -C policy load
> > > > pushd tests/filesystem
> > > > sudo runcon -t test_filesystem_t ./create_file -f trans_test_file \
> > > >       -e test_filesystem_filetranscon_t -v
> > > > sudo rm -f trans_test_file
> > > > popd
> > > > sudo make -C policy unload
> > > > popd
> > > > sudo umount /mnt/selinux-testsuite
> > > > sudo exportfs -u localhost:$MOUNT
> > > > sudo rmdir /mnt/selinux-testsuite
> > > > sudo systemctl stop nfs-server
> > > >
> > > > Expected output:
> > > > <eliding noise from commands run prior to or after the test itself>
> > > > Process context:
> > > >       unconfined_u:unconfined_r:test_filesystem_t:s0-s0:c0.c1023
> > > > Created file: trans_test_file
> > > > File context: unconfined_u:object_r:test_filesystem_filetranscon_t:s0
> > > > File context is correct
> > > >
> > > > Actual output:
> > > > <eliding noise from commands run prior to or after the test itself>
> > > > Process context:
> > > >       unconfined_u:unconfined_r:test_filesystem_t:s0-s0:c0.c1023
> > > > Created file: trans_test_file
> > > > File context: system_u:object_r:test_file_t:s0
> > > > File context error, expected:
> > > >       test_filesystem_filetranscon_t
> > > > got:
> > > >       test_file_t
> > > >
> > > > Signed-off-by: Stephen Smalley <stephen.smalley.work at gmail.com>
> > > > ---
> > > > v3 removes the erroneous and unnecessary change to NFSv2 and updates the
> > > > description to note the possible origin of the bug. I did not add a
> > > > Fixes tag however as I have not yet tried confirming that.
> > >
> > > I think this bug has always been present - since label support was
> > > added.
> > > Commit d6a97d3f589a ("NFSD: add security label to struct nfsd_attrs")
> > > should have fixed it, but was missing the extra test that you provide.
> > >
> > > So
> > > Fixes: 0c71b7ed5de8 ("nfsd: introduce file_cache_mutex")
> > > might be appropriate - it fixes the patch, though not a bug introduced
> > > by the patch.
> > >
> > > Thanks for this patch!
> > > Reviewed-by: NeilBrown <neilb at suse.de>
> >
> > FWIW, I finally got around to testing Linux v5.14 and it did pass
> > these NFS tests so this was a regression. I haven't been able to
> > bisect yet.
>
> Seems to have broken sometime between v5.19 and v6.0. Still bisecting.

git bisect ended with:
[d6a97d3f589a3a46a16183e03f3774daee251317] NFSD: add security label to
struct nfsd_attrs
as the breaking commit.

Bisecting was a little complicated by other unrelated bugs but I
narrowed it to just this particular one.