Re: [PATCH 5/7] pipe: reject F_SETPIPE_SZ with size over UINT_MAX

Kees Cook
2018-01-09T22:24:26Z

On Sun, Jan 7, 2018 at 9:35 PM, Eric Biggers <ebiggers3@gmail.com> wrote:
> From: Eric Biggers <ebiggers@google.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@google.com>

Acked-by: Kees Cook <keescook@chromium.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