[PATCH v2 1/2] [security] Add new hook to compare new mount to an existing mount
Casey Schaufler
casey at schaufler-ca.com
Fri Feb 19 16:45:01 UTC 2021
On 2/19/2021 8:25 AM, Olga Kornievskaia wrote:
> On Thu, Feb 18, 2021 at 4:57 PM Casey Schaufler <casey at schaufler-ca.com> wrote:
>> On 2/18/2021 11:50 AM, Olga Kornievskaia wrote:
>>> From: Olga Kornievskaia <kolga at 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.
>>>
>>> Signed-off-by: Olga Kornievskaia <kolga at netapp.com>
>>> `
>>> ---
>>> 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 | 54 +++++++++++++++++++++++++++++++++++
>>> 5 files changed, 76 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..77c1e9cdeaca 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 existing mount options are compatible with the new
>>> + * mount options being used.
>>> + * @sb superblock being compared
>>> + * @mnt_opts new mount options
>>> + * Return 0 if options are the same.
>> s/the same/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..f0b8ebc1e2c2 100644
>>> --- a/security/selinux/hooks.c
>>> +++ b/security/selinux/hooks.c
>>> @@ -2656,6 +2656,59 @@ 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
>> Please maintain the existing comment style used in this file.
> I'm again not sure what exactly is the style used in this file and how
> is this inconsistent?
While not 100% consistent, the style used here has the "/*" alone on the first line
with the text starting on the second line.
/*
* Like this
* is done
*/
not
/* Like this
* is done
*/
>
> Here's one example from this file:
> /* Wake up the parent if it is waiting so that it can recheck
> * wait permission to the new task SID. */
> this is another example from this file:
> /* Check whether the new SID can inherit signal state from the old SID.
> * If not, clear itimers to avoid subsequent signal generation and
> * flush and unblock signals.
> *
> * This must occur _after_ the task SID has been updated so that any
> * kill done after the flush will be checked against the new SID.
> */
> Here's another:
> /* strip quotes */
>
> What exactly is not correct about the new comment?
> /* superblock not initialized (i.e. no options) - reject if any
> * options specified, otherwise accept
> */
> It uses "/*" and has a space after. It starts each new line with "*"
> and a space. And ends with a new line. This is consistent with the
> general kernel style. Actually example 1 is not following kernel style
> by not ending on the new line.
>
> Is the objection that it's perhaps not a sentence that starts with a
> capital letter and ends with a period? Not all comments are sentences.
> If so please specify. Otherwise, I'm just guessing what you are
> expecting.
>
>
>> /*
>> * 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 +7037,7 @@ 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),
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