Re: [PATCH 1/7] pipe, sysctl: drop 'min' parameter from pipe-max-size converter

[Kees Cook <keescook@chromium.org>]

On Sun, Jan 7, 2018 at 9:35 PM, Eric Biggers <ebiggers3@gmail.com> wrote:
> From: Eric Biggers <ebiggers@google.com>
>
> Before validating the given value against pipe_min_size,
> do_proc_dopipe_max_size_conv() calls round_pipe_size(), which rounds the
> value up to pipe_min_size.  Therefore, the second check against
> pipe_min_size is redundant.  Remove it.

Well, it's not redundant: it provides a hint to anyone trying to tweak
the sysctl about the minimum value. I think this should stay, but that
pipe_min_size should be made const.

-Kees

>
> Signed-off-by: Eric Biggers <ebiggers@google.com>
> ---
>  fs/pipe.c                 | 10 +++-------
>  include/linux/pipe_fs_i.h |  2 +-
>  kernel/sysctl.c           | 15 +--------------
>  3 files changed, 5 insertions(+), 22 deletions(-)
>
> diff --git a/fs/pipe.c b/fs/pipe.c
> index 6d98566201ef..a75f5d2ca99c 100644
> --- a/fs/pipe.c
> +++ b/fs/pipe.c
> @@ -35,11 +35,6 @@
>   */
>  unsigned int pipe_max_size = 1048576;
>
> -/*
> - * Minimum pipe size, as required by POSIX
> - */
> -unsigned int pipe_min_size = PAGE_SIZE;
> -
>  /* Maximum allocatable pages per user. Hard limit is unset by default, soft
>   * matches default values.
>   */
> @@ -1024,8 +1019,9 @@ unsigned int round_pipe_size(unsigned int size)
>  {
>         unsigned long nr_pages;
>
> -       if (size < pipe_min_size)
> -               size = pipe_min_size;
> +       /* Minimum pipe size, as required by POSIX */
> +       if (size < PAGE_SIZE)
> +               size = PAGE_SIZE;
>
>         nr_pages = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
>         if (nr_pages == 0)
> diff --git a/include/linux/pipe_fs_i.h b/include/linux/pipe_fs_i.h
> index 2dc5e9870fcd..7d9beda14584 100644
> --- a/include/linux/pipe_fs_i.h
> +++ b/include/linux/pipe_fs_i.h
> @@ -167,7 +167,7 @@ void pipe_lock(struct pipe_inode_info *);
>  void pipe_unlock(struct pipe_inode_info *);
>  void pipe_double_lock(struct pipe_inode_info *, struct pipe_inode_info *);
>
> -extern unsigned int pipe_max_size, pipe_min_size;
> +extern unsigned int pipe_max_size;
>  extern unsigned long pipe_user_pages_hard;
>  extern unsigned long pipe_user_pages_soft;
>  int pipe_proc_fn(struct ctl_table *, int, void __user *, size_t *, loff_t *);
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index 557d46728577..a71ebb5c5182 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -1820,7 +1820,6 @@ static struct ctl_table fs_table[] = {
>                 .maxlen         = sizeof(pipe_max_size),
>                 .mode           = 0644,
>                 .proc_handler   = &pipe_proc_fn,
> -               .extra1         = &pipe_min_size,
>         },
>         {
>                 .procname       = "pipe-user-pages-hard",
> @@ -2622,16 +2621,10 @@ int proc_douintvec_minmax(struct ctl_table *table, int write,
>                                  do_proc_douintvec_minmax_conv, &param);
>  }
>
> -struct do_proc_dopipe_max_size_conv_param {
> -       unsigned int *min;
> -};
> -
>  static int do_proc_dopipe_max_size_conv(unsigned long *lvalp,
>                                         unsigned int *valp,
>                                         int write, void *data)
>  {
> -       struct do_proc_dopipe_max_size_conv_param *param = data;
> -
>         if (write) {
>                 unsigned int val;
>
> @@ -2642,9 +2635,6 @@ static int do_proc_dopipe_max_size_conv(unsigned long *lvalp,
>                 if (val == 0)
>                         return -EINVAL;
>
> -               if (param->min && *param->min > val)
> -                       return -ERANGE;
> -
>                 *valp = val;
>         } else {
>                 unsigned int val = *valp;
> @@ -2657,11 +2647,8 @@ static int do_proc_dopipe_max_size_conv(unsigned long *lvalp,
>  int proc_dopipe_max_size(struct ctl_table *table, int write,
>                          void __user *buffer, size_t *lenp, loff_t *ppos)
>  {
> -       struct do_proc_dopipe_max_size_conv_param param = {
> -               .min = (unsigned int *) table->extra1,
> -       };
>         return do_proc_douintvec(table, write, buffer, lenp, ppos,
> -                                do_proc_dopipe_max_size_conv, &param);
> +                                do_proc_dopipe_max_size_conv, NULL);
>  }
>
>  static void validate_coredump_safety(void)
> --
> 2.15.1
>



-- 
Kees Cook
Pixel Security