linux-kernel - Re: [patch] timerfd add flags check

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Date:	Tue, 10 Feb 2009 13:36:42 +1300
From:	Michael Kerrisk <mtk.manpages@...glemail.com>
To:	Davide Libenzi <davidel@...ilserver.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Greg KH <greg@...ah.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [patch] timerfd add flags check

On Tue, Feb 10, 2009 at 12:31 PM, Davide Libenzi
<davidel@...ilserver.org> wrote:
> Like Michael requested, this patch adds a missing check for valid flags in
> timerfd_settime(), and make it return EINVAL in case some extra bits are
> set.
>
> Michael said:
> If this is to be any use to userland apps that want to check flag
> support (perhaps it is too late already), then the sooner we get it
> into the kernel the better: 2.6.29 would be good; earlier stables as
> well would be even better.
>
> Acked-by: Michael Kerrisk <mtk.manpages@...il.com>
>
>
> Signed-off-by: Davide Libenzi <davidel@...ilserver.org>

Davide, one question: is the TFD_FLAGS_SET constant below needed?

cheers,

Michael

> ---
>  fs/timerfd.c            |   12 ++++++------
>  include/linux/timerfd.h |   17 ++++++++++++++---
>  2 files changed, 20 insertions(+), 9 deletions(-)
>
> Index: linux-2.6.mod/fs/timerfd.c
> ===================================================================
> --- linux-2.6.mod.orig/fs/timerfd.c     2009-02-08 18:36:45.000000000 -0800
> +++ linux-2.6.mod/fs/timerfd.c  2009-02-08 18:53:32.000000000 -0800
> @@ -186,10 +186,9 @@ SYSCALL_DEFINE2(timerfd_create, int, clo
>        BUILD_BUG_ON(TFD_CLOEXEC != O_CLOEXEC);
>        BUILD_BUG_ON(TFD_NONBLOCK != O_NONBLOCK);
>
> -       if (flags & ~(TFD_CLOEXEC | TFD_NONBLOCK))
> -               return -EINVAL;
> -       if (clockid != CLOCK_MONOTONIC &&
> -           clockid != CLOCK_REALTIME)
> +       if ((flags & ~TFD_CREATE_FLAGS) ||
> +           (clockid != CLOCK_MONOTONIC &&
> +            clockid != CLOCK_REALTIME))
>                return -EINVAL;
>
>        ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
> @@ -201,7 +200,7 @@ SYSCALL_DEFINE2(timerfd_create, int, clo
>        hrtimer_init(&ctx->tmr, clockid, HRTIMER_MODE_ABS);
>
>        ufd = anon_inode_getfd("[timerfd]", &timerfd_fops, ctx,
> -                              flags & (O_CLOEXEC | O_NONBLOCK));
> +                              flags & TFD_SHARED_FCNTL_FLAGS);
>        if (ufd < 0)
>                kfree(ctx);
>
> @@ -219,7 +218,8 @@ SYSCALL_DEFINE4(timerfd_settime, int, uf
>        if (copy_from_user(&ktmr, utmr, sizeof(ktmr)))
>                return -EFAULT;
>
> -       if (!timespec_valid(&ktmr.it_value) ||
> +       if ((flags & ~TFD_SETTIME_FLAGS) ||
> +           !timespec_valid(&ktmr.it_value) ||
>            !timespec_valid(&ktmr.it_interval))
>                return -EINVAL;
>
> Index: linux-2.6.mod/include/linux/timerfd.h
> ===================================================================
> --- linux-2.6.mod.orig/include/linux/timerfd.h  2009-02-08 18:36:45.000000000 -0800
> +++ linux-2.6.mod/include/linux/timerfd.h       2009-02-08 18:41:22.000000000 -0800
> @@ -11,13 +11,24 @@
>  /* For O_CLOEXEC and O_NONBLOCK */
>  #include <linux/fcntl.h>
>
> -/* Flags for timerfd_settime.  */
> +/*
> + * CAREFUL: Check include/asm-generic/fcntl.h when defining
> + * new flags, since they might collide with O_* ones. We want
> + * to re-use O_* flags that couldn't possibly have a meaning
> + * from eventfd, in order to leave a free define-space for
> + * shared O_* flags.
> + */
>  #define TFD_TIMER_ABSTIME (1 << 0)
> -
> -/* Flags for timerfd_create.  */
>  #define TFD_CLOEXEC O_CLOEXEC
>  #define TFD_NONBLOCK O_NONBLOCK
>
> +#define TFD_SHARED_FCNTL_FLAGS (TFD_CLOEXEC | TFD_NONBLOCK)
> +/* Flags for timerfd_create.  */
> +#define TFD_CREATE_FLAGS TFD_SHARED_FCNTL_FLAGS
> +/* Flags for timerfd_settime.  */
> +#define TFD_SETTIME_FLAGS TFD_TIMER_ABSTIME
> +#define TFD_FLAGS_SET (TFD_SHARED_FCNTL_FLAGS | TFD_TIMER_ABSTIME)
> +
>
>  #endif /* _LINUX_TIMERFD_H */
>
>



-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
git://git.kernel.org/pub/scm/docs/man-pages/man-pages.git
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