On Fri, 26 May 2017, Stephen Smalley wrote:
> On Thu, 2017-05-25 at 17:07 -0400, Scott Mayhew wrote:
> > When the client traverses from filesystem exported without the
> > "security_label" option to one exported with the "security_label"
> > option, it needs to pass SECURITY_LSM_NATIVE_LABELS to
> > security_sb_set_mnt_opts() so that the new superblock has SBLABEL_MNT
> > set in its security mount options. Otherwise, attempts to set
> > security
> > labels via setxattr over NFSv4.2 will fail.
> >
> > Signed-off-by: Scott Mayhew <smayhew@xxxxxxxxxx>
> > ---
> > fs/nfs/super.c | 23 ++++++++++++++++++++++-
> > 1 file changed, 22 insertions(+), 1 deletion(-)
> >
> > diff --git a/fs/nfs/super.c b/fs/nfs/super.c
> > index 2f3822a..d7a3b89 100644
> > --- a/fs/nfs/super.c
> > +++ b/fs/nfs/super.c
> > @@ -2544,10 +2544,31 @@ EXPORT_SYMBOL_GPL(nfs_set_sb_security);
> > int nfs_clone_sb_security(struct super_block *s, struct dentry
> > *mntroot,
> > struct nfs_mount_info *mount_info)
> > {
> > + int error;
> > + unsigned long kflags = 0, kflags_out = 0;
> > + struct security_mnt_opts opts;
> > +
> > /* clone any lsm security options from the parent to the new
> > sb */
> > if (d_inode(mntroot)->i_op != NFS_SB(s)->nfs_client-
> > >rpc_ops->dir_inode_ops)
> > return -ESTALE;
> > - return security_sb_clone_mnt_opts(mount_info->cloned->sb,
> > s);
> > + error = security_sb_clone_mnt_opts(mount_info->cloned->sb,
> > s);
> > + if (error)
> > + goto err;
> > +
> > + if (NFS_SB(s)->caps & NFS_CAP_SECURITY_LABEL &&
> > + !(NFS_SB(mount_info->cloned->sb)->caps &
> > NFS_CAP_SECURITY_LABEL)) {
> > + memset(&opts, 0, sizeof(opts));
> > + kflags |= SECURITY_LSM_NATIVE_LABELS;
> > +
> > + error = security_sb_set_mnt_opts(s, &opts, kflags,
> > &kflags_out);
> > + if (error)
> > + goto err;
> > +
> > + if (!(kflags_out & SECURITY_LSM_NATIVE_LABELS))
> > + NFS_SB(s)->caps &= ~NFS_CAP_SECURITY_LABEL;
> > + }
> > +err:
> > + return error;
> > }
> > EXPORT_SYMBOL_GPL(nfs_clone_sb_security);
>
> Could this clobber a context set via context= mount option?
Argh, yes I suppose it could. In my first attempt to fix this, I added
a security_sb_get_mnt_opts() hook to get the original mount options and
then passed that along with the SECURITY_LSM_NATIVE_LABELS flag to
security_sb_set_mnt_opts(). When I saw that security_sb_set_mnt_opts()
wouldn't allow me to change a superblock that had already been
initialized, I got rid of the hook and added the check in patch 1...
maybe a combination of the two is needed?
Testing it again now, I'm not sure the context= mount option is working
correctly with the latest kernel.
-Scott
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