On Thu, 01 Jun 2017, Stephen Smalley wrote:
> On Thu, 2017-06-01 at 10:46 -0400, Scott Mayhew wrote:
> > When an NFSv4 client performs a mount operation, it first mounts the
> > NFSv4 root and then does path walk to the exported path and performs
> > a
> > submount on that, cloning the security mount options from the root's
> > superblock to the submount's superblock in the process.
> >
> > Unless the NFS server has an explicit fsid=0 export with the
> > "security_label" option, the NFSv4 root superblock will not have
> > SBLABEL_MNT set, and neither will the submount superblock after
> > cloning
> > the security mount options. As a result, setxattr's of security
> > labels
> > over NFSv4.2 will fail. In a similar fashion, NFSv4.2 mounts mounted
> > with the context= mount option will not show the correct labels
> > because
> > the nfs_server->caps flags of the cloned superblock will still have
> > NFS_CAP_SECURITY_LABEL set.
> >
> > Allowing the NFSv4 client to enable or disable
> > SECURITY_LSM_NATIVE_LABELS
> > behavior will ensure that the SBLABEL_MNT flag has the correct value
> > when the client traverses from an exported path without the
> > "security_label" option to one with the "security_label" option and
> > vice versa. Similarly, checking to see if SECURITY_LSM_NATIVE_LABELS
> > is
> > set upon return from security_sb_clone_mnt_opts() and clearing
> > NFS_CAP_SECURITY_LABEL if necessary will allow the correct labels to
> > be displayed for NFSv4.2 mounts mounted with the context= mount
> > option.
> >
> > Signed-off-by: Scott Mayhew <smayhew@xxxxxxxxxx>
> > ---
> > fs/nfs/super.c | 18 +++++++++++++++++-
> > include/linux/lsm_hooks.h | 4 +++-
> > include/linux/security.h | 8 ++++++--
> > security/security.c | 7 +++++--
> > security/selinux/hooks.c | 43
> > ++++++++++++++++++++++++++++++++++++++-----
> > 5 files changed, 69 insertions(+), 11 deletions(-)
> >
> > diff --git a/fs/nfs/super.c b/fs/nfs/super.c
> > index 2f3822a..6a11535 100644
> > --- a/fs/nfs/super.c
> > +++ b/fs/nfs/super.c
> > @@ -2544,10 +2544,26 @@ 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;
> > +
> > /* 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);
> > +
> > + if (NFS_SB(s)->caps & NFS_CAP_SECURITY_LABEL)
> > + kflags |= SECURITY_LSM_NATIVE_LABELS;
> > +
> > + error = security_sb_clone_mnt_opts(mount_info->cloned->sb,
> > s, kflags, &kflags_out);
> > + if (error)
> > + goto err;
>
> Not sure this is justified; coding style says to just return directly
> if no cleanup is required.
>
> > +
> > + if (NFS_SB(s)->caps & NFS_CAP_SECURITY_LABEL &&
> > + !(kflags_out & SECURITY_LSM_NATIVE_LABELS))
> > + NFS_SB(s)->caps &= ~NFS_CAP_SECURITY_LABEL;
> > +err:
> > + return error;
> > +
> > }
> > EXPORT_SYMBOL_GPL(nfs_clone_sb_security);
> >
> > diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> > index 080f34e..2f54bfb 100644
> > --- a/include/linux/lsm_hooks.h
> > +++ b/include/linux/lsm_hooks.h
> > @@ -1388,7 +1388,9 @@ union security_list_options {
> > unsigned long kern_flags,
> > unsigned long *set_kern_flags);
> > int (*sb_clone_mnt_opts)(const struct super_block *oldsb,
> > - struct super_block *newsb);
> > + struct super_block *newsb,
> > + unsigned long kern_flags,
> > + unsigned long
> > *set_kern_flags);
> > int (*sb_parse_opts_str)(char *options, struct
> > security_mnt_opts *opts);
> > int (*dentry_init_security)(struct dentry *dentry, int mode,
> > const struct qstr *name,
> > void **ctx,
> > diff --git a/include/linux/security.h b/include/linux/security.h
> > index af675b5..a55ae9c 100644
> > --- a/include/linux/security.h
> > +++ b/include/linux/security.h
> > @@ -240,7 +240,9 @@ int security_sb_set_mnt_opts(struct super_block
> > *sb,
> > unsigned long kern_flags,
> > unsigned long *set_kern_flags);
> > int security_sb_clone_mnt_opts(const struct super_block *oldsb,
> > - struct super_block *newsb);
> > + struct super_block *newsb,
> > + unsigned long kern_flags,
> > + unsigned long *set_kern_flags);
> > int security_sb_parse_opts_str(char *options, struct
> > security_mnt_opts *opts);
> > int security_dentry_init_security(struct dentry *dentry, int mode,
> > const struct qstr *name,
> > void **ctx,
> > @@ -581,7 +583,9 @@ static inline int security_sb_set_mnt_opts(struct
> > super_block *sb,
> > }
> >
> > static inline int security_sb_clone_mnt_opts(const struct
> > super_block *oldsb,
> > - struct super_block
> > *newsb)
> > + struct super_block
> > *newsb,
> > + unsigned long
> > kern_flags,
> > + unsigned long
> > *set_kern_flags)
> > {
> > return 0;
> > }
> > diff --git a/security/security.c b/security/security.c
> > index b9fea39..7b70ea2 100644
> > --- a/security/security.c
> > +++ b/security/security.c
> > @@ -380,9 +380,12 @@ int security_sb_set_mnt_opts(struct super_block
> > *sb,
> > EXPORT_SYMBOL(security_sb_set_mnt_opts);
> >
> > int security_sb_clone_mnt_opts(const struct super_block *oldsb,
> > - struct super_block *newsb)
> > + struct super_block *newsb,
> > + unsigned long kern_flags,
> > + unsigned long *set_kern_flags)
> > {
> > - return call_int_hook(sb_clone_mnt_opts, 0, oldsb, newsb);
> > + return call_int_hook(sb_clone_mnt_opts, 0, oldsb, newsb,
> > + kern_flags, set_kern_flags);
> > }
> > EXPORT_SYMBOL(security_sb_clone_mnt_opts);
> >
> > diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> > index e67a526..80d9acf 100644
> > --- a/security/selinux/hooks.c
> > +++ b/security/selinux/hooks.c
> > @@ -529,8 +529,14 @@ static int sb_finish_set_opts(struct super_block
> > *sb)
> > sb->s_id, sb->s_type->name);
> >
> > sbsec->flags |= SE_SBINITIALIZED;
> > +
> > + /* Explicitly set or clear SBLABEL_MNT. It's not sufficient
> > to simply
> > + leave the flag untouched because sb_clone_mnt_opts might
> > be handing
> > + us a superblock that needs the flag to be cleared. */
>
> Coding style (and checkpatch.pl) prefer a different style for multi-
> line comments.
>
> > if (selinux_is_sblabel_mnt(sb))
> > sbsec->flags |= SBLABEL_MNT;
> > + else
> > + sbsec->flags &= ~SBLABEL_MNT;
> >
> > /* Initialize the root inode. */
> > rc = inode_doinit_with_dentry(root_inode, root);
> > @@ -963,8 +969,11 @@ static int selinux_cmp_sb_context(const struct
> > super_block *oldsb,
> > }
> >
> > static int selinux_sb_clone_mnt_opts(const struct super_block
> > *oldsb,
> > - struct super_block *newsb)
> > + struct super_block *newsb,
> > + unsigned long kern_flags,
> > + unsigned long
> > *set_kern_flags)
> > {
> > + int rc = 0;
> > const struct superblock_security_struct *oldsbsec = oldsb-
> > >s_security;
> > struct superblock_security_struct *newsbsec = newsb-
> > >s_security;
> >
> > @@ -977,14 +986,23 @@ static int selinux_sb_clone_mnt_opts(const
> > struct super_block *oldsb,
> > * mount options. thus we can safely deal with this
> > superblock later
> > */
> > if (!ss_initialized)
> > - return 0;
> > + goto out;
>
> Likewise, don't see the point of this since no cleanup is required, and
> as per coding style.
>
> > +
> > + if (kern_flags && !set_kern_flags) {
> > + /* Specifying internal flags without providing a
> > place to
> > + * place the results is not allowed */
> > + rc = -EINVAL;
> > + goto out;
>
> Ditto, just return directly.
>
> > + }
> >
> > /* how can we clone if the old one wasn't set up?? */
> > BUG_ON(!(oldsbsec->flags & SE_SBINITIALIZED));
> >
> > /* if fs is reusing a sb, make sure that the contexts match
> > */
> > - if (newsbsec->flags & SE_SBINITIALIZED)
> > - return selinux_cmp_sb_context(oldsb, newsb);
> > + if (newsbsec->flags & SE_SBINITIALIZED) {
> > + rc = selinux_cmp_sb_context(oldsb, newsb);
> > + goto out;
> > + }
>
> And again.
>
> >
> > mutex_lock(&newsbsec->lock);
> >
> > @@ -994,6 +1012,19 @@ static int selinux_sb_clone_mnt_opts(const
> > struct super_block *oldsb,
> > newsbsec->def_sid = oldsbsec->def_sid;
> > newsbsec->behavior = oldsbsec->behavior;
> >
> > + if (newsbsec->behavior == SECURITY_FS_USE_NATIVE
> > + && !(kern_flags &
> > SECURITY_LSM_NATIVE_LABELS)
> > + && !set_context) {
>
> I prefer ending the prior line with &&, not beginning the next one with
> it. Also indentation of the continuation lines seems excessive.
>
> > + rc = security_fs_use(newsb);
> > + if (rc)
> > + goto out_unlock;
> > + }
> > +
> > + if (kern_flags & SECURITY_LSM_NATIVE_LABELS && !set_context)
> > {
> > + newsbsec->behavior = SECURITY_FS_USE_NATIVE;
> > + *set_kern_flags |= SECURITY_LSM_NATIVE_LABELS;
> > + }
> > +
> > if (set_context) {
> > u32 sid = oldsbsec->mntpoint_sid;
> >
> > @@ -1013,8 +1044,10 @@ static int selinux_sb_clone_mnt_opts(const
> > struct super_block *oldsb,
> > }
> >
> > sb_finish_set_opts(newsb);
> > +out_unlock:
> > mutex_unlock(&newsbsec->lock);
> > - return 0;
> > +out:
> > + return rc;
> > }
> >
> > static int selinux_parse_opts_str(char *options,
Again, my fault... I should've run checkpatch.pl.
I'll address all these and re-send.
-Scott
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