Return-Path: Received: from smtp.nsa.gov ([8.44.101.8]:18063 "EHLO emsm-gh1-uea10.nsa.gov" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751122AbdFASZp (ORCPT ); Thu, 1 Jun 2017 14:25:45 -0400 Message-ID: <1496341807.27759.15.camel@tycho.nsa.gov> Subject: Re: [PATCH] security/selinux: allow security_sb_clone_mnt_opts to enable/disable native labeling behavior From: Stephen Smalley To: Scott Mayhew , selinux@tycho.nsa.gov, linux-nfs@vger.kernel.org Cc: Paul Moore , Eric Paris , Trond Myklebust , "J . Bruce Fields" Date: Thu, 01 Jun 2017 14:30:07 -0400 In-Reply-To: <20170601144628.26535-1-smayhew@redhat.com> References: <1495813358.4586.1.camel@tycho.nsa.gov> <20170601144628.26535-1-smayhew@redhat.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Sender: linux-nfs-owner@vger.kernel.org List-ID: 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 > --- >  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,