linux-kernel - Re: [PATCH 5/7] pipe: reject F_SETPIPE_SZ with size over UINT

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Date:   Tue, 9 Jan 2018 14:24:22 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Eric Biggers <ebiggers3@...il.com>
Cc:     "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Willy Tarreau <w@....eu>,
        Mikulas Patocka <mpatocka@...hat.com>,
        "Luis R . Rodriguez" <mcgrof@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Eric Biggers <ebiggers@...gle.com>
Subject: Re: [PATCH 5/7] pipe: reject F_SETPIPE_SZ with size over UINT_MAX

On Sun, Jan 7, 2018 at 9:35 PM, Eric Biggers <ebiggers3@...il.com> wrote:
> From: Eric Biggers <ebiggers@...gle.com>
>
> A pipe's size is represented as an 'unsigned int'.  As expected, writing
> a value greater than UINT_MAX to /proc/sys/fs/pipe-max-size fails with
> EINVAL.  However, the F_SETPIPE_SZ fcntl silently truncates such values
> to 32 bits, rather than failing with EINVAL as expected.  (It *does*
> fail with EINVAL for values above (1 << 31) but <= UINT_MAX.)
>
> Fix this by moving the check against UINT_MAX into round_pipe_size()
> which is called in both cases.
>
> Signed-off-by: Eric Biggers <ebiggers@...gle.com>

Acked-by: Kees Cook <keescook@...omium.org>

-Kees

> ---
>  fs/pipe.c                 | 5 ++++-
>  include/linux/pipe_fs_i.h | 2 +-
>  kernel/sysctl.c           | 3 ---
>  3 files changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/fs/pipe.c b/fs/pipe.c
> index 9f20e7128578..f1ee1e599495 100644
> --- a/fs/pipe.c
> +++ b/fs/pipe.c
> @@ -1020,10 +1020,13 @@ const struct file_operations pipefifo_fops = {
>   * Currently we rely on the pipe array holding a power-of-2 number
>   * of pages. Returns 0 on error.
>   */
> -unsigned int round_pipe_size(unsigned int size)
> +unsigned int round_pipe_size(unsigned long size)
>  {
>         unsigned long nr_pages;
>
> +       if (size > UINT_MAX)
> +               return 0;
> +
>         /* Minimum pipe size, as required by POSIX */
>         if (size < PAGE_SIZE)
>                 size = PAGE_SIZE;
> diff --git a/include/linux/pipe_fs_i.h b/include/linux/pipe_fs_i.h
> index 5028bd4b2c96..5a3bb3b7c9ad 100644
> --- a/include/linux/pipe_fs_i.h
> +++ b/include/linux/pipe_fs_i.h
> @@ -190,6 +190,6 @@ long pipe_fcntl(struct file *, unsigned int, unsigned long arg);
>  struct pipe_inode_info *get_pipe_info(struct file *file);
>
>  int create_pipe_files(struct file **, int);
> -unsigned int round_pipe_size(unsigned int size);
> +unsigned int round_pipe_size(unsigned long size);
>
>  #endif
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index 33e2f0f02000..31fe10fd745f 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -2630,9 +2630,6 @@ static int do_proc_dopipe_max_size_conv(unsigned long *lvalp,
>         if (write) {
>                 unsigned int val;
>
> -               if (*lvalp > UINT_MAX)
> -                       return -EINVAL;
> -
>                 val = round_pipe_size(*lvalp);
>                 if (val == 0)
>                         return -EINVAL;
> --
> 2.15.1
>



-- 
Kees Cook
Pixel Security