linux-kernel - Re: [PATCH 20/23] y2038: move itimer reset into itimer.c

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Date:   Sat, 9 Nov 2019 14:43:06 +0100
From:   Ondrej Mosnacek <omosnace@...hat.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     y2038@...ts.linaro.org, John Stultz <john.stultz@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Paul Moore <paul@...l-moore.com>,
        Stephen Smalley <sds@...ho.nsa.gov>,
        Eric Paris <eparis@...isplace.org>,
        Linux kernel mailing list <linux-kernel@...r.kernel.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Anna-Maria Gleixner <anna-maria@...utronix.de>,
        Al Viro <viro@...iv.linux.org.uk>,
        SElinux list <selinux@...r.kernel.org>
Subject: Re: [PATCH 20/23] y2038: move itimer reset into itimer.c

On Fri, Nov 8, 2019 at 10:18 PM Arnd Bergmann <arnd@...db.de> wrote:
> Preparing for a change to the itimer internals, stop using the
> do_setitimer() symbol and instead use a new higher-level interface.
>
> The do_getitimer()/do_setitimer functions can now be made static,
> allowing the compiler to potentially produce better object code.
>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  include/linux/time.h     |  9 +++++----
>  kernel/time/itimer.c     | 15 +++++++++++++--
>  security/selinux/hooks.c | 10 +++-------
>  3 files changed, 21 insertions(+), 13 deletions(-)
>
> diff --git a/include/linux/time.h b/include/linux/time.h
> index 27d83fd2ae61..0760a4f5a15c 100644
> --- a/include/linux/time.h
> +++ b/include/linux/time.h
> @@ -35,10 +35,11 @@ extern time64_t mktime64(const unsigned int year, const unsigned int mon,
>  extern u32 (*arch_gettimeoffset)(void);
>  #endif
>
> -struct itimerval;
> -extern int do_setitimer(int which, struct itimerval *value,
> -                       struct itimerval *ovalue);
> -extern int do_getitimer(int which, struct itimerval *value);
> +#ifdef CONFIG_POSIX_TIMERS
> +extern void clear_itimer(void);
> +#else
> +static inline void clear_itimer(void) {}
> +#endif
>
>  extern long do_utimes(int dfd, const char __user *filename, struct timespec64 *times, int flags);
>
> diff --git a/kernel/time/itimer.c b/kernel/time/itimer.c
> index 4664c6addf69..ce9cd19ce72e 100644
> --- a/kernel/time/itimer.c
> +++ b/kernel/time/itimer.c
> @@ -73,7 +73,7 @@ static void get_cpu_itimer(struct task_struct *tsk, unsigned int clock_id,
>         value->it_interval = ns_to_timeval(interval);
>  }
>
> -int do_getitimer(int which, struct itimerval *value)
> +static int do_getitimer(int which, struct itimerval *value)
>  {
>         struct task_struct *tsk = current;
>
> @@ -197,7 +197,7 @@ static void set_cpu_itimer(struct task_struct *tsk, unsigned int clock_id,
>  #define timeval_valid(t) \
>         (((t)->tv_sec >= 0) && (((unsigned long) (t)->tv_usec) < USEC_PER_SEC))
>
> -int do_setitimer(int which, struct itimerval *value, struct itimerval *ovalue)
> +static int do_setitimer(int which, struct itimerval *value, struct itimerval *ovalue)
>  {
>         struct task_struct *tsk = current;
>         struct hrtimer *timer;
> @@ -249,6 +249,17 @@ int do_setitimer(int which, struct itimerval *value, struct itimerval *ovalue)
>         return 0;
>  }
>
> +#ifdef CONFIG_SECURITY_SELINUX

Did you mean "#ifdef CONFIG_POSIX_TIMERS" here to match the header?

> +void clear_itimer(void)
> +{
> +       struct itimerval v = {};
> +       int i;
> +
> +       for (i = 0; i < 3; i++)
> +               do_setitimer(i, &v, NULL);
> +}
> +#endif
> +
>  #ifdef __ARCH_WANT_SYS_ALARM
>
>  /**
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 9625b99e677f..c3f2e89acb87 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -2549,9 +2549,8 @@ static void selinux_bprm_committing_creds(struct linux_binprm *bprm)
>  static void selinux_bprm_committed_creds(struct linux_binprm *bprm)
>  {
>         const struct task_security_struct *tsec = selinux_cred(current_cred());
> -       struct itimerval itimer;
>         u32 osid, sid;
> -       int rc, i;
> +       int rc;
>
>         osid = tsec->osid;
>         sid = tsec->sid;
> @@ -2569,11 +2568,8 @@ static void selinux_bprm_committed_creds(struct linux_binprm *bprm)
>         rc = avc_has_perm(&selinux_state,
>                           osid, sid, SECCLASS_PROCESS, PROCESS__SIGINH, NULL);
>         if (rc) {
> -               if (IS_ENABLED(CONFIG_POSIX_TIMERS)) {
> -                       memset(&itimer, 0, sizeof itimer);
> -                       for (i = 0; i < 3; i++)
> -                               do_setitimer(i, &itimer, NULL);
> -               }
> +               if (IS_ENABLED(CONFIG_POSIX_TIMERS))
> +                       clear_itimer();

Since you already define a no-op fallback for the case of
!IS_ENABLED(CONFIG_POSIX_TIMERS) in time.h, why not simply call
clear_itimer() unconditionally?

>                 spin_lock_irq(&current->sighand->siglock);
>                 if (!fatal_signal_pending(current)) {
>                         flush_sigqueue(&current->pending);
> --
> 2.20.0
>

-- 
Ondrej Mosnacek <omosnace at redhat dot com>
Software Engineer, Security Technologies
Red Hat, Inc.