Re: [PATCH] [PATCH] LSM: generalize flag passing to security_capable

[Micah Morton <mortonm@chromium.org>]

Any comments on this patch? If not, could it get merged at some point?

I booted a Linux kernel with the changes compiled in and verified with
print statements that the code works properly AFAICT.
On Mon, Nov 19, 2018 at 10:54 AM <mortonm@chromium.org> wrote:
>
> From: Micah Morton <mortonm@chromium.org>
>
> This patch provides a general mechanism for passing flags to the
> security_capable LSM hook. It replaces the specific 'audit' flag that is
> used to tell security_capable whether it should log an audit message for
> the given capability check. The reason for generalizing this flag
> passing is so we can add an additional flag that signifies whether
> security_capable is being called by a setid syscall (which is needed by
> the proposed SafeSetID LSM). This generalization could also support
> passing down the inode for CAP_DAC_OVERRIDE/READ_SEARCH checks so that
> authorization could happen on a per-file basis for specific files rather
> than all or nothing.
>
> Signed-off-by: Micah Morton <mortonm@chromium.org>
> ---
>
> Developed against the 'next-general' branch.
>
> @Stephen: is this the approach you had in mind for modifying the
> callers of ns_capable?
>
>  include/linux/lsm_hooks.h     |  8 ++++---
>  include/linux/security.h      | 35 ++++++++++++++++++++----------
>  kernel/capability.c           | 41 +++++++++++++++++++++++++++--------
>  kernel/seccomp.c              |  7 ++++--
>  security/apparmor/lsm.c       |  4 ++--
>  security/commoncap.c          | 27 ++++++++++++++++-------
>  security/security.c           | 14 +++++-------
>  security/selinux/hooks.c      | 13 ++++++-----
>  security/smack/smack_access.c |  5 ++++-
>  9 files changed, 103 insertions(+), 51 deletions(-)
>
> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> index aaeb7fa24dc4..02422592cc83 100644
> --- a/include/linux/lsm_hooks.h
> +++ b/include/linux/lsm_hooks.h
> @@ -1270,7 +1270,7 @@
>   *     @cred contains the credentials to use.
>   *     @ns contains the user namespace we want the capability in
>   *     @cap contains the capability <include/linux/capability.h>.
> - *     @audit contains whether to write an audit message or not
> + *     @opts contains options for the capable check <include/linux/security.h>
>   *     Return 0 if the capability is granted for @tsk.
>   * @syslog:
>   *     Check permission before accessing the kernel message ring or changing
> @@ -1446,8 +1446,10 @@ union security_list_options {
>                         const kernel_cap_t *effective,
>                         const kernel_cap_t *inheritable,
>                         const kernel_cap_t *permitted);
> -       int (*capable)(const struct cred *cred, struct user_namespace *ns,
> -                       int cap, int audit);
> +       int (*capable)(const struct cred *cred,
> +                       struct user_namespace *ns,
> +                       int cap,
> +                       struct security_capable_opts *opts);
>         int (*quotactl)(int cmds, int type, int id, struct super_block *sb);
>         int (*quota_on)(struct dentry *dentry);
>         int (*syslog)(int type);
> diff --git a/include/linux/security.h b/include/linux/security.h
> index d170a5b031f3..b60621e93faf 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -58,6 +58,13 @@ struct mm_struct;
>  #define SECURITY_CAP_NOAUDIT 0
>  #define SECURITY_CAP_AUDIT 1
>
> +struct security_capable_opts {
> +       /* If capable should audit the security request */
> +       bool log_audit_message;
> +       /* If capable is being called from a setid syscall */
> +       bool in_setid;
> +};
> +
>  /* LSM Agnostic defines for sb_set_mnt_opts */
>  #define SECURITY_LSM_NATIVE_LABELS     1
>
> @@ -72,7 +79,7 @@ enum lsm_event {
>
>  /* These functions are in security/commoncap.c */
>  extern int cap_capable(const struct cred *cred, struct user_namespace *ns,
> -                      int cap, int audit);
> +                      int cap, struct security_capable_opts *opts);
>  extern int cap_settime(const struct timespec64 *ts, const struct timezone *tz);
>  extern int cap_ptrace_access_check(struct task_struct *child, unsigned int mode);
>  extern int cap_ptrace_traceme(struct task_struct *parent);
> @@ -180,6 +187,13 @@ static inline const char *kernel_load_data_id_str(enum kernel_load_data_id id)
>         return kernel_load_data_str[id];
>  }
>
> +/* init a security_capable_opts struct with default values */
> +static inline void init_security_capable_opts(struct security_capable_opts* opts)
> +{
> +       opts->log_audit_message = true;
> +       opts->in_setid = false;
> +}
> +
>  #ifdef CONFIG_SECURITY
>
>  struct security_mnt_opts {
> @@ -233,10 +247,10 @@ int security_capset(struct cred *new, const struct cred *old,
>                     const kernel_cap_t *effective,
>                     const kernel_cap_t *inheritable,
>                     const kernel_cap_t *permitted);
> -int security_capable(const struct cred *cred, struct user_namespace *ns,
> -                       int cap);
> -int security_capable_noaudit(const struct cred *cred, struct user_namespace *ns,
> -                            int cap);
> +int security_capable(const struct cred *cred,
> +                      struct user_namespace *ns,
> +                      int cap,
> +                      struct security_capable_opts *opts);
>  int security_quotactl(int cmds, int type, int id, struct super_block *sb);
>  int security_quota_on(struct dentry *dentry);
>  int security_syslog(int type);
> @@ -492,14 +506,11 @@ static inline int security_capset(struct cred *new,
>  }
>
>  static inline int security_capable(const struct cred *cred,
> -                                  struct user_namespace *ns, int cap)
> +                                  struct user_namespace *ns,
> +                                  int cap,
> +                                  struct security_capable_opts *opts)
>  {
> -       return cap_capable(cred, ns, cap, SECURITY_CAP_AUDIT);
> -}
> -
> -static inline int security_capable_noaudit(const struct cred *cred,
> -                                          struct user_namespace *ns, int cap) {
> -       return cap_capable(cred, ns, cap, SECURITY_CAP_NOAUDIT);
> +       return cap_capable(cred, ns, cap, opts);
>  }
>
>  static inline int security_quotactl(int cmds, int type, int id,
> diff --git a/kernel/capability.c b/kernel/capability.c
> index 1e1c0236f55b..d8ff27e6e7c4 100644
> --- a/kernel/capability.c
> +++ b/kernel/capability.c
> @@ -297,9 +297,12 @@ bool has_ns_capability(struct task_struct *t,
>                        struct user_namespace *ns, int cap)
>  {
>         int ret;
> +       struct security_capable_opts opts;
> +
> +       init_security_capable_opts(&opts);
>
>         rcu_read_lock();
> -       ret = security_capable(__task_cred(t), ns, cap);
> +       ret = security_capable(__task_cred(t), ns, cap, &opts);
>         rcu_read_unlock();
>
>         return (ret == 0);
> @@ -338,9 +341,13 @@ bool has_ns_capability_noaudit(struct task_struct *t,
>                                struct user_namespace *ns, int cap)
>  {
>         int ret;
> +       struct security_capable_opts opts;
> +
> +       init_security_capable_opts(&opts);
> +       opts.log_audit_message = false;
>
>         rcu_read_lock();
> -       ret = security_capable_noaudit(__task_cred(t), ns, cap);
> +       ret = security_capable(__task_cred(t), ns, cap, &opts);
>         rcu_read_unlock();
>
>         return (ret == 0);
> @@ -363,7 +370,9 @@ bool has_capability_noaudit(struct task_struct *t, int cap)
>         return has_ns_capability_noaudit(t, &init_user_ns, cap);
>  }
>
> -static bool ns_capable_common(struct user_namespace *ns, int cap, bool audit)
> +static bool ns_capable_common(struct user_namespace *ns,
> +                             int cap,
> +                             struct security_capable_opts *opts)
>  {
>         int capable;
>
> @@ -372,8 +381,7 @@ static bool ns_capable_common(struct user_namespace *ns, int cap, bool audit)
>                 BUG();
>         }
>
> -       capable = audit ? security_capable(current_cred(), ns, cap) :
> -                         security_capable_noaudit(current_cred(), ns, cap);
> +       capable = security_capable(current_cred(), ns, cap, opts);
>         if (capable == 0) {
>                 current->flags |= PF_SUPERPRIV;
>                 return true;
> @@ -394,7 +402,10 @@ static bool ns_capable_common(struct user_namespace *ns, int cap, bool audit)
>   */
>  bool ns_capable(struct user_namespace *ns, int cap)
>  {
> -       return ns_capable_common(ns, cap, true);
> +       struct security_capable_opts opts;
> +
> +       init_security_capable_opts(&opts);
> +       return ns_capable_common(ns, cap, &opts);
>  }
>  EXPORT_SYMBOL(ns_capable);
>
> @@ -412,7 +423,11 @@ EXPORT_SYMBOL(ns_capable);
>   */
>  bool ns_capable_noaudit(struct user_namespace *ns, int cap)
>  {
> -       return ns_capable_common(ns, cap, false);
> +       struct security_capable_opts opts;
> +
> +       init_security_capable_opts(&opts);
> +       opts.log_audit_message = false;
> +       return ns_capable_common(ns, cap, &opts);
>  }
>  EXPORT_SYMBOL(ns_capable_noaudit);
>
> @@ -448,10 +463,13 @@ EXPORT_SYMBOL(capable);
>  bool file_ns_capable(const struct file *file, struct user_namespace *ns,
>                      int cap)
>  {
> +       struct security_capable_opts opts;
> +
>         if (WARN_ON_ONCE(!cap_valid(cap)))
>                 return false;
>
> -       if (security_capable(file->f_cred, ns, cap) == 0)
> +       init_security_capable_opts(&opts);
> +       if (security_capable(file->f_cred, ns, cap, &opts) == 0)
>                 return true;
>
>         return false;
> @@ -500,10 +518,15 @@ bool ptracer_capable(struct task_struct *tsk, struct user_namespace *ns)
>  {
>         int ret = 0;  /* An absent tracer adds no restrictions */
>         const struct cred *cred;
> +       struct security_capable_opts opts;
> +
> +       init_security_capable_opts(&opts);
> +       opts.log_audit_message = false;
> +
>         rcu_read_lock();
>         cred = rcu_dereference(tsk->ptracer_cred);
>         if (cred)
> -               ret = security_capable_noaudit(cred, ns, CAP_SYS_PTRACE);
> +               ret = security_capable(cred, ns, CAP_SYS_PTRACE, &opts);
>         rcu_read_unlock();
>         return (ret == 0);
>  }
> diff --git a/kernel/seccomp.c b/kernel/seccomp.c
> index f2ae2324c232..eed0e34c1bc2 100644
> --- a/kernel/seccomp.c
> +++ b/kernel/seccomp.c
> @@ -370,12 +370,15 @@ static struct seccomp_filter *seccomp_prepare_filter(struct sock_fprog *fprog)
>         struct seccomp_filter *sfilter;
>         int ret;
>         const bool save_orig = IS_ENABLED(CONFIG_CHECKPOINT_RESTORE);
> +       struct security_capable_opts opts;
>
>         if (fprog->len == 0 || fprog->len > BPF_MAXINSNS)
>                 return ERR_PTR(-EINVAL);
>
>         BUG_ON(INT_MAX / fprog->len < sizeof(struct sock_filter));
>
> +       init_security_capable_opts(&opts);
> +       opts.log_audit_message = false;
>         /*
>          * Installing a seccomp filter requires that the task has
>          * CAP_SYS_ADMIN in its namespace or be running with no_new_privs.
> @@ -383,8 +386,8 @@ static struct seccomp_filter *seccomp_prepare_filter(struct sock_fprog *fprog)
>          * behavior of privileged children.
>          */
>         if (!task_no_new_privs(current) &&
> -           security_capable_noaudit(current_cred(), current_user_ns(),
> -                                    CAP_SYS_ADMIN) != 0)
> +           security_capable(current_cred(), current_user_ns(),
> +                                    CAP_SYS_ADMIN, &opts) != 0)
>                 return ERR_PTR(-EACCES);
>
>         /* Allocate a new seccomp_filter */
> diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
> index 42446a216f3b..3be87dfd5e57 100644
> --- a/security/apparmor/lsm.c
> +++ b/security/apparmor/lsm.c
> @@ -176,14 +176,14 @@ static int apparmor_capget(struct task_struct *target, kernel_cap_t *effective,
>  }
>
>  static int apparmor_capable(const struct cred *cred, struct user_namespace *ns,
> -                           int cap, int audit)
> +                           int cap, struct security_capable_opts *opts)
>  {
>         struct aa_label *label;
>         int error = 0;
>
>         label = aa_get_newest_cred_label(cred);
>         if (!unconfined(label))
> -               error = aa_capable(label, cap, audit);
> +               error = aa_capable(label, cap, opts->log_audit_message);
>         aa_put_label(label);
>
>         return error;
> diff --git a/security/commoncap.c b/security/commoncap.c
> index 18a4fdf6f6eb..93fbb0dd70d6 100644
> --- a/security/commoncap.c
> +++ b/security/commoncap.c
> @@ -69,7 +69,7 @@ static void warn_setuid_and_fcaps_mixed(const char *fname)
>   * kernel's capable() and has_capability() returns 1 for this case.
>   */
>  int cap_capable(const struct cred *cred, struct user_namespace *targ_ns,
> -               int cap, int audit)
> +               int cap, struct security_capable_opts *opts)
>  {
>         struct user_namespace *ns = targ_ns;
>
> @@ -223,12 +223,14 @@ int cap_capget(struct task_struct *target, kernel_cap_t *effective,
>   */
>  static inline int cap_inh_is_capped(void)
>  {
> +       struct security_capable_opts opts;
>
> +       init_security_capable_opts(&opts);
>         /* they are so limited unless the current task has the CAP_SETPCAP
>          * capability
>          */
>         if (cap_capable(current_cred(), current_cred()->user_ns,
> -                       CAP_SETPCAP, SECURITY_CAP_AUDIT) == 0)
> +                       CAP_SETPCAP, &opts) == 0)
>                 return 0;
>         return 1;
>  }
> @@ -1174,6 +1176,7 @@ int cap_task_prctl(int option, unsigned long arg2, unsigned long arg3,
>  {
>         const struct cred *old = current_cred();
>         struct cred *new;
> +       struct security_capable_opts opts;
>
>         switch (option) {
>         case PR_CAPBSET_READ:
> @@ -1204,13 +1207,15 @@ int cap_task_prctl(int option, unsigned long arg2, unsigned long arg3,
>          * capability-based-privilege environment.
>          */
>         case PR_SET_SECUREBITS:
> +               init_security_capable_opts(&opts);
>                 if ((((old->securebits & SECURE_ALL_LOCKS) >> 1)
>                      & (old->securebits ^ arg2))                        /*[1]*/
>                     || ((old->securebits & SECURE_ALL_LOCKS & ~arg2))   /*[2]*/
>                     || (arg2 & ~(SECURE_ALL_LOCKS | SECURE_ALL_BITS))   /*[3]*/
>                     || (cap_capable(current_cred(),
> -                                   current_cred()->user_ns, CAP_SETPCAP,
> -                                   SECURITY_CAP_AUDIT) != 0)           /*[4]*/
> +                                   current_cred()->user_ns,
> +                                   CAP_SETPCAP,
> +                                   &opts) != 0)                        /*[4]*/
>                         /*
>                          * [1] no changing of bits that are locked
>                          * [2] no unlocking of locks
> @@ -1304,10 +1309,14 @@ int cap_task_prctl(int option, unsigned long arg2, unsigned long arg3,
>  int cap_vm_enough_memory(struct mm_struct *mm, long pages)
>  {
>         int cap_sys_admin = 0;
> +       struct security_capable_opts opts;
>
> -       if (cap_capable(current_cred(), &init_user_ns, CAP_SYS_ADMIN,
> -                       SECURITY_CAP_NOAUDIT) == 0)
> +       init_security_capable_opts(&opts);
> +       opts.log_audit_message = false;
> +
> +       if (cap_capable(current_cred(), &init_user_ns, CAP_SYS_ADMIN, &opts) == 0)
>                 cap_sys_admin = 1;
> +
>         return cap_sys_admin;
>  }
>
> @@ -1323,10 +1332,12 @@ int cap_vm_enough_memory(struct mm_struct *mm, long pages)
>  int cap_mmap_addr(unsigned long addr)
>  {
>         int ret = 0;
> +       struct security_capable_opts opts;
>
> +        init_security_capable_opts(&opts);
>         if (addr < dac_mmap_min_addr) {
> -               ret = cap_capable(current_cred(), &init_user_ns, CAP_SYS_RAWIO,
> -                                 SECURITY_CAP_AUDIT);
> +               ret = cap_capable(current_cred(), &init_user_ns,
> +                                               CAP_SYS_RAWIO, &opts);
>                 /* set PF_SUPERPRIV if it turns out we allow the low mmap */
>                 if (ret == 0)
>                         current->flags |= PF_SUPERPRIV;
> diff --git a/security/security.c b/security/security.c
> index 04d173eb93f6..bbc400a90c34 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -294,16 +294,12 @@ int security_capset(struct cred *new, const struct cred *old,
>                                 effective, inheritable, permitted);
>  }
>
> -int security_capable(const struct cred *cred, struct user_namespace *ns,
> -                    int cap)
> +int security_capable(const struct cred *cred,
> +                    struct user_namespace *ns,
> +                    int cap,
> +                    struct security_capable_opts *opts)
>  {
> -       return call_int_hook(capable, 0, cred, ns, cap, SECURITY_CAP_AUDIT);
> -}
> -
> -int security_capable_noaudit(const struct cred *cred, struct user_namespace *ns,
> -                            int cap)
> -{
> -       return call_int_hook(capable, 0, cred, ns, cap, SECURITY_CAP_NOAUDIT);
> +       return call_int_hook(capable, 0, cred, ns, cap, opts);
>  }
>
>  int security_quotactl(int cmds, int type, int id, struct super_block *sb)
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 7ce683259357..ebd36adc8856 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -2316,9 +2316,10 @@ static int selinux_capset(struct cred *new, const struct cred *old,
>   */
>
>  static int selinux_capable(const struct cred *cred, struct user_namespace *ns,
> -                          int cap, int audit)
> +                          int cap, struct security_capable_opts *opts)
>  {
> -       return cred_has_capability(cred, cap, audit, ns == &init_user_ns);
> +       return cred_has_capability(cred, cap, opts->log_audit_message,
> +                                                       ns == &init_user_ns);
>  }
>
>  static int selinux_quotactl(int cmds, int type, int id, struct super_block *sb)
> @@ -3245,11 +3246,13 @@ static int selinux_inode_getattr(const struct path *path)
>  static bool has_cap_mac_admin(bool audit)
>  {
>         const struct cred *cred = current_cred();
> -       int cap_audit = audit ? SECURITY_CAP_AUDIT : SECURITY_CAP_NOAUDIT;
> +       struct security_capable_opts opts;
>
> -       if (cap_capable(cred, &init_user_ns, CAP_MAC_ADMIN, cap_audit))
> +       init_security_capable_opts(&opts);
> +       opts.log_audit_message = audit ? true : false;
> +       if (cap_capable(cred, &init_user_ns, CAP_MAC_ADMIN, &opts))
>                 return false;
> -       if (cred_has_capability(cred, CAP_MAC_ADMIN, cap_audit, true))
> +       if (cred_has_capability(cred, CAP_MAC_ADMIN, opts.log_audit_message, true))
>                 return false;
>         return true;
>  }
> diff --git a/security/smack/smack_access.c b/security/smack/smack_access.c
> index 9a4c0ad46518..eca364b697d7 100644
> --- a/security/smack/smack_access.c
> +++ b/security/smack/smack_access.c
> @@ -639,8 +639,11 @@ bool smack_privileged_cred(int cap, const struct cred *cred)
>         struct smack_known *skp = tsp->smk_task;
>         struct smack_known_list_elem *sklep;
>         int rc;
> +       struct security_capable_opts opts;
>
> -       rc = cap_capable(cred, &init_user_ns, cap, SECURITY_CAP_AUDIT);
> +       init_security_capable_opts(&opts);
> +
> +       rc = cap_capable(cred, &init_user_ns, cap, &opts);
>         if (rc)
>                 return false;
>
> --
> 2.19.1.1215.g8438c0b245-goog
>