Re: [PATCH v4 1/3] [security] Add new hook to compare new mount to an existing mount

[Casey Schaufler <casey@schaufler-ca.com>]

On 3/2/2021 10:20 AM, Anna Schumaker wrote:
> Hi Casey,
>
> On Fri, Feb 26, 2021 at 10:40 PM Olga Kornievskaia
> <olga.kornievskaia@gmail.com> wrote:
>> From: Olga Kornievskaia <kolga@netapp.com>
>>
>> Add a new hook that takes an existing super block and a new mount
>> with new options and determines if new options confict with an
>> existing mount or not.
>>
>> A filesystem can use this new hook to determine if it can share
>> the an existing superblock with a new superblock for the new mount.
>>
>> Signed-off-by: Olga Kornievskaia <kolga@netapp.com>
> Do you have any other thoughts on this patch? I'm also wondering how
> you want to handle sending it upstream. 

James Morris is the maintainer for the security sub-system,
so you'll want to send this through him. He will want you to
have an ACK from Paul Moore, who is the SELinux maintainer.

> I'm happy to take it through
> the NFS tree (with an acked-by) for a 5.12-rc with Olga's bugfix
> patches, but if you have other thoughts or plans then let me know!
>
> Thanks,
> Anna
>
>> ---
>>  include/linux/lsm_hook_defs.h |  1 +
>>  include/linux/lsm_hooks.h     |  6 ++++
>>  include/linux/security.h      |  8 +++++
>>  security/security.c           |  7 +++++
>>  security/selinux/hooks.c      | 56 +++++++++++++++++++++++++++++++++++
>>  5 files changed, 78 insertions(+)
>>
>> diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
>> index 7aaa753b8608..1b12a5266a51 100644
>> --- a/include/linux/lsm_hook_defs.h
>> +++ b/include/linux/lsm_hook_defs.h
>> @@ -62,6 +62,7 @@ LSM_HOOK(int, 0, sb_alloc_security, struct super_block *sb)
>>  LSM_HOOK(void, LSM_RET_VOID, sb_free_security, struct super_block *sb)
>>  LSM_HOOK(void, LSM_RET_VOID, sb_free_mnt_opts, void *mnt_opts)
>>  LSM_HOOK(int, 0, sb_eat_lsm_opts, char *orig, void **mnt_opts)
>> +LSM_HOOK(int, 0, sb_mnt_opts_compat, struct super_block *sb, void *mnt_opts)
>>  LSM_HOOK(int, 0, sb_remount, struct super_block *sb, void *mnt_opts)
>>  LSM_HOOK(int, 0, sb_kern_mount, struct super_block *sb)
>>  LSM_HOOK(int, 0, sb_show_options, struct seq_file *m, struct super_block *sb)
>> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
>> index a19adef1f088..0de8eb2ea547 100644
>> --- a/include/linux/lsm_hooks.h
>> +++ b/include/linux/lsm_hooks.h
>> @@ -142,6 +142,12 @@
>>   *     @orig the original mount data copied from userspace.
>>   *     @copy copied data which will be passed to the security module.
>>   *     Returns 0 if the copy was successful.
>> + * @sb_mnt_opts_compat:
>> + *     Determine if the new mount options in @mnt_opts are allowed given
>> + *     the existing mounted filesystem at @sb.
>> + *     @sb superblock being compared
>> + *     @mnt_opts new mount options
>> + *     Return 0 if options are compatible.
>>   * @sb_remount:
>>   *     Extracts security system specific mount options and verifies no changes
>>   *     are being made to those options.
>> diff --git a/include/linux/security.h b/include/linux/security.h
>> index c35ea0ffccd9..50db3d5d1608 100644
>> --- a/include/linux/security.h
>> +++ b/include/linux/security.h
>> @@ -291,6 +291,7 @@ int security_sb_alloc(struct super_block *sb);
>>  void security_sb_free(struct super_block *sb);
>>  void security_free_mnt_opts(void **mnt_opts);
>>  int security_sb_eat_lsm_opts(char *options, void **mnt_opts);
>> +int security_sb_mnt_opts_compat(struct super_block *sb, void *mnt_opts);
>>  int security_sb_remount(struct super_block *sb, void *mnt_opts);
>>  int security_sb_kern_mount(struct super_block *sb);
>>  int security_sb_show_options(struct seq_file *m, struct super_block *sb);
>> @@ -635,6 +636,13 @@ static inline int security_sb_remount(struct super_block *sb,
>>         return 0;
>>  }
>>
>> +static inline int security_sb_mnt_opts_compat(struct super_block *sb,
>> +                                             void *mnt_opts)
>> +{
>> +       return 0;
>> +}
>> +
>> +
>>  static inline int security_sb_kern_mount(struct super_block *sb)
>>  {
>>         return 0;
>> diff --git a/security/security.c b/security/security.c
>> index 7b09cfbae94f..56cf5563efde 100644
>> --- a/security/security.c
>> +++ b/security/security.c
>> @@ -890,6 +890,13 @@ int security_sb_eat_lsm_opts(char *options, void **mnt_opts)
>>  }
>>  EXPORT_SYMBOL(security_sb_eat_lsm_opts);
>>
>> +int security_sb_mnt_opts_compat(struct super_block *sb,
>> +                               void *mnt_opts)
>> +{
>> +       return call_int_hook(sb_mnt_opts_compat, 0, sb, mnt_opts);
>> +}
>> +EXPORT_SYMBOL(security_sb_mnt_opts_compat);
>> +
>>  int security_sb_remount(struct super_block *sb,
>>                         void *mnt_opts)
>>  {
>> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
>> index 644b17ec9e63..afee3a222a0e 100644
>> --- a/security/selinux/hooks.c
>> +++ b/security/selinux/hooks.c
>> @@ -2656,6 +2656,61 @@ static int selinux_sb_eat_lsm_opts(char *options, void **mnt_opts)
>>         return rc;
>>  }
>>
>> +static int selinux_sb_mnt_opts_compat(struct super_block *sb, void *mnt_opts)
>> +{
>> +       struct selinux_mnt_opts *opts = mnt_opts;
>> +       struct superblock_security_struct *sbsec = sb->s_security;
>> +       u32 sid;
>> +       int rc;
>> +
>> +       /*
>> +        * Superblock not initialized (i.e. no options) - reject if any
>> +        * options specified, otherwise accept.
>> +        */
>> +       if (!(sbsec->flags & SE_SBINITIALIZED))
>> +               return opts ? 1 : 0;
>> +
>> +       /*
>> +        * Superblock initialized and no options specified - reject if
>> +        * superblock has any options set, otherwise accept.
>> +        */
>> +       if (!opts)
>> +               return (sbsec->flags & SE_MNTMASK) ? 1 : 0;
>> +
>> +       if (opts->fscontext) {
>> +               rc = parse_sid(sb, opts->fscontext, &sid);
>> +               if (rc)
>> +                       return 1;
>> +               if (bad_option(sbsec, FSCONTEXT_MNT, sbsec->sid, sid))
>> +                       return 1;
>> +       }
>> +       if (opts->context) {
>> +               rc = parse_sid(sb, opts->context, &sid);
>> +               if (rc)
>> +                       return 1;
>> +               if (bad_option(sbsec, CONTEXT_MNT, sbsec->mntpoint_sid, sid))
>> +                       return 1;
>> +       }
>> +       if (opts->rootcontext) {
>> +               struct inode_security_struct *root_isec;
>> +
>> +               root_isec = backing_inode_security(sb->s_root);
>> +               rc = parse_sid(sb, opts->rootcontext, &sid);
>> +               if (rc)
>> +                       return 1;
>> +               if (bad_option(sbsec, ROOTCONTEXT_MNT, root_isec->sid, sid))
>> +                       return 1;
>> +       }
>> +       if (opts->defcontext) {
>> +               rc = parse_sid(sb, opts->defcontext, &sid);
>> +               if (rc)
>> +                       return 1;
>> +               if (bad_option(sbsec, DEFCONTEXT_MNT, sbsec->def_sid, sid))
>> +                       return 1;
>> +       }
>> +       return 0;
>> +}
>> +
>>  static int selinux_sb_remount(struct super_block *sb, void *mnt_opts)
>>  {
>>         struct selinux_mnt_opts *opts = mnt_opts;
>> @@ -6984,6 +7039,7 @@ static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = {
>>
>>         LSM_HOOK_INIT(sb_free_security, selinux_sb_free_security),
>>         LSM_HOOK_INIT(sb_free_mnt_opts, selinux_free_mnt_opts),
>> +       LSM_HOOK_INIT(sb_mnt_opts_compat, selinux_sb_mnt_opts_compat),
>>         LSM_HOOK_INIT(sb_remount, selinux_sb_remount),
>>         LSM_HOOK_INIT(sb_kern_mount, selinux_sb_kern_mount),
>>         LSM_HOOK_INIT(sb_show_options, selinux_sb_show_options),
>> --
>> 2.27.0
>>