Re: [PATCH 1/2] pipe: check limits only when increasing pipe capacity

Vegard Nossum
2016-08-16T11:55:39Z

On 08/16/2016 01:10 PM, Michael Kerrisk (man-pages) wrote:
> When changing a pipe's capacity with fcntl(F_SETPIPE_SZ), various
> limits defined by /proc/sys/fs/pipe-* files are checked to see
> if unprivileged users are exceeding limits on memory consumption.
>
[...]

> ---
> fs/pipe.c | 25 +++++++++++++++++--------
> 1 file changed, 17 insertions(+), 8 deletions(-)
>
> diff --git a/fs/pipe.c b/fs/pipe.c
> index 4ebe6b2..a98ebca 100644
> --- a/fs/pipe.c
> +++ b/fs/pipe.c
> @@ -1122,14 +1122,23 @@ long pipe_fcntl(struct file *file, unsigned int cmd, unsigned long arg)
> if (!nr_pages)
> goto out;
>
> - if (!capable(CAP_SYS_RESOURCE) && size > pipe_max_size) {
> - ret = -EPERM;
> - goto out;
> - } else if ((too_many_pipe_buffers_hard(pipe->user) ||
> - too_many_pipe_buffers_soft(pipe->user)) &&
> - !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN)) {
> - ret = -EPERM;
> - goto out;
> + /*
> + * If trying to increase the pipe capacity, check that an
> + * unprivileged user is not trying to exceed various limits.
> + * (Decreasing the pipe capacity is always permitted, even
> + * if the user is currently over a limit.)
> + */
> + if (nr_pages > pipe->buffers) {
> + if (!capable(CAP_SYS_RESOURCE) && size > pipe_max_size) {
> + ret = -EPERM;
> + goto out;
> + } else if ((too_many_pipe_buffers_hard(pipe->user) ||
> + too_many_pipe_buffers_soft(pipe->user)) &&
> + !capable(CAP_SYS_RESOURCE) &&
> + !capable(CAP_SYS_ADMIN)) {
> + ret = -EPERM;
> + goto out;
> + }
> }
> ret = pipe_set_size(pipe, nr_pages);
> break;
>

FWIW: Reviewed-by: Vegard Nossum <vegard.nossum@oracle.com>

Vegard