From: "NeilBrown" <neilb@suse.de>
To: "Stephen Smalley" <stephen.smalley.work@gmail.com>
Cc: selinux@vger.kernel.org, linux-nfs@vger.kernel.org,
chuck.lever@oracle.com, jlayton@kernel.org, paul@paul-moore.com,
omosnace@redhat.com, linux-security-module@vger.kernel.org
Subject: Re: [PATCH v3] nfsd: set security label during create operations
Date: Wed, 08 May 2024 16:54:25 +1000 [thread overview]
Message-ID: <171515126555.4857.14866053620991695880@noble.neil.brown.name> (raw)
In-Reply-To: <CAEjxPJ6W7UGvPUMt82+_tB2MPmcmG7JaUjH6HhgjwTqOzQL_xA@mail.gmail.com>
On Tue, 07 May 2024, Stephen Smalley wrote:
> On Mon, May 6, 2024 at 1:46 AM NeilBrown <neilb@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@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@suse.de>
> >
> > NeilBrown
>
> Thanks for confirming. Do we need to also check for the ACL case in
> nfsd_attrs_valid() or is that covered in some other way?
>
Thanks a good question. I should have asked it myself!
No, ACLs aren't covered some other way. They have the same problem.
I'm tempted to suggest that we simple drop the guard and call
nfsd_setattr() unconditionally. The cost is primarily the we call
inode_lock() without needing to do anything.
Maybe moving the test inside nfsd_setattr() makes it a bit more obvious
what is needed:
diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index 2e41eb4c3cec..c738e9dfd72f 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -499,6 +499,14 @@ nfsd_setattr(struct svc_rqst *rqstp, struct svc_fh *fhp,
bool size_change = (iap->ia_valid & ATTR_SIZE);
int retries;
+ if (!(iap->ia_valid ||
+ (attr->na_seclabel && attr->na_seclabel->len) ||
+ (IS_ENABLED(CONFIG_FS_POSIX_ACL) && attr->na_pacl) ||
+ (IS_ENABLED(CONFIG_FS_POSIX_ACL) &&
+ !attr->na_aclerr && attr->na_dpacl && S_ISDIR(inode->i_mode))))
+ /* Don't bother with inode_lock() */
+ goto out;
+
if (iap->ia_valid & ATTR_SIZE) {
accmode |= NFSD_MAY_WRITE|NFSD_MAY_OWNER_OVERRIDE;
ftype = S_IFREG;
@@ -1418,14 +1426,7 @@ nfsd_create_setattr(struct svc_rqst *rqstp, struct svc_fh *fhp,
if (!uid_eq(current_fsuid(), GLOBAL_ROOT_UID))
iap->ia_valid &= ~(ATTR_UID|ATTR_GID);
- /*
- * Callers expect new file metadata to be committed even
- * if the attributes have not changed.
- */
- if (iap->ia_valid)
- status = nfsd_setattr(rqstp, resfhp, attrs, NULL);
- else
- status = nfserrno(commit_metadata(resfhp));
+ status = nfsd_setattr(rqstp, resfhp, attrs, NULL);
/*
* Transactional filesystems had a chance to commit changes
Thoughts?
Thanks,
NeilBrown
next prev parent reply other threads:[~2024-05-08 6:54 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-03 13:09 [PATCH v3] nfsd: set security label during create operations Stephen Smalley
2024-05-03 17:31 ` Jeffrey Layton
2024-05-04 15:23 ` Chuck Lever
2024-05-06 5:46 ` NeilBrown
2024-05-06 16:31 ` Stephen Smalley
2024-05-08 6:54 ` NeilBrown [this message]
2024-05-15 14:52 ` Stephen Smalley
2024-05-16 17:29 ` Stephen Smalley
2024-05-22 17:29 ` Stephen Smalley
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=171515126555.4857.14866053620991695880@noble.neil.brown.name \
--to=neilb@suse.de \
--cc=chuck.lever@oracle.com \
--cc=jlayton@kernel.org \
--cc=linux-nfs@vger.kernel.org \
--cc=linux-security-module@vger.kernel.org \
--cc=omosnace@redhat.com \
--cc=paul@paul-moore.com \
--cc=selinux@vger.kernel.org \
--cc=stephen.smalley.work@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).