Quoting Tyler Hicks (tyhi...@canonical.com):
> When checking the current cred for a capability in a specific user
> namespace, it isn't always desirable to have the LSMs audit the check.
> This patch adds a noaudit variant of ns_capable() for when those
> situations arise.
>
> The common logic between ns_capable() and the new ns_capable_noaudit()
> is moved into a single, shared function to keep duplicated code to a
> minimum and ease maintainability.
>
> Signed-off-by: Tyler Hicks <tyhi...@canonical.com>
Acked-by: Serge E. Hallyn <serge.hal...@ubuntu.com>
> ---
> include/linux/capability.h | 5 +++++
> kernel/capability.c | 46
> ++++++++++++++++++++++++++++++++++++----------
> 2 files changed, 41 insertions(+), 10 deletions(-)
>
> diff --git a/include/linux/capability.h b/include/linux/capability.h
> index 00690ff..5f3c63d 100644
> --- a/include/linux/capability.h
> +++ b/include/linux/capability.h
> @@ -206,6 +206,7 @@ extern bool has_ns_capability_noaudit(struct task_struct
> *t,
> struct user_namespace *ns, int cap);
> extern bool capable(int cap);
> extern bool ns_capable(struct user_namespace *ns, int cap);
> +extern bool ns_capable_noaudit(struct user_namespace *ns, int cap);
> #else
> static inline bool has_capability(struct task_struct *t, int cap)
> {
> @@ -233,6 +234,10 @@ static inline bool ns_capable(struct user_namespace *ns,
> int cap)
> {
> return true;
> }
> +static inline bool ns_capable_noaudit(struct user_namespace *ns, int cap)
> +{
> + return true;
> +}
> #endif /* CONFIG_MULTIUSER */
> extern bool capable_wrt_inode_uidgid(const struct inode *inode, int cap);
> extern bool file_ns_capable(const struct file *file, struct user_namespace
> *ns, int cap);
> diff --git a/kernel/capability.c b/kernel/capability.c
> index 45432b5..00411c8 100644
> --- a/kernel/capability.c
> +++ b/kernel/capability.c
> @@ -361,6 +361,24 @@ 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)
> +{
> + int capable;
> +
> + if (unlikely(!cap_valid(cap))) {
> + pr_crit("capable() called with invalid cap=%u\n", cap);
> + BUG();
> + }
> +
> + capable = audit ? security_capable(current_cred(), ns, cap) :
> + security_capable_noaudit(current_cred(), ns, cap);
> + if (capable == 0) {
> + current->flags |= PF_SUPERPRIV;
> + return true;
> + }
> + return false;
> +}
> +
> /**
> * ns_capable - Determine if the current task has a superior capability in
> effect
> * @ns: The usernamespace we want the capability in
> @@ -374,19 +392,27 @@ bool has_capability_noaudit(struct task_struct *t, int
> cap)
> */
> bool ns_capable(struct user_namespace *ns, int cap)
> {
> - if (unlikely(!cap_valid(cap))) {
> - pr_crit("capable() called with invalid cap=%u\n", cap);
> - BUG();
> - }
> -
> - if (security_capable(current_cred(), ns, cap) == 0) {
> - current->flags |= PF_SUPERPRIV;
> - return true;
> - }
> - return false;
> + return ns_capable_common(ns, cap, true);
> }
> EXPORT_SYMBOL(ns_capable);
>
> +/**
> + * ns_capable_noaudit - Determine if the current task has a superior
> capability
> + * (unaudited) in effect
> + * @ns: The usernamespace we want the capability in
> + * @cap: The capability to be tested for
> + *
> + * Return true if the current task has the given superior capability
> currently
> + * available for use, false if not.
> + *
> + * This sets PF_SUPERPRIV on the task if the capability is available on the
> + * assumption that it's about to be used.
> + */
> +bool ns_capable_noaudit(struct user_namespace *ns, int cap)
> +{
> + return ns_capable_common(ns, cap, false);
> +}
> +EXPORT_SYMBOL(ns_capable_noaudit);
>
> /**
> * capable - Determine if the current task has a superior capability in
> effect
> --
> 2.7.4
>
