Re: [PATCH v2 1/4] fs/pipe: Limit the slots in pipe_resize_ring()

Oleg Nesterov
2025-03-07T14:52:14Z

On 03/07, K Prateek Nayak wrote:
>
> --- a/fs/pipe.c
> +++ b/fs/pipe.c
> @@ -1271,6 +1271,10 @@ int pipe_resize_ring(struct pipe_inode_info *pipe, unsigned int nr_slots)
> struct pipe_buffer *bufs;
> unsigned int head, tail, mask, n;
>
> + /* nr_slots larger than limits of pipe->{head,tail} */
> + if (unlikely(nr_slots > (pipe_index_t)-1u))
> + return -EINVAL;

The whole series look "obviously" good to me,

Reviewed-by: Oleg Nesterov <oleg@redhat.com>

-------------------------------------------------------------------------------
But damn ;) lets look at round_pipe_size(),

unsigned int round_pipe_size(unsigned int size)
{
if (size > (1U << 31))
return 0;

/* Minimum pipe size, as required by POSIX */
if (size < PAGE_SIZE)
return PAGE_SIZE;

return roundup_pow_of_two(size);
}

it is a bit silly to allow the maximum size == 1U << 31 in pipe_set_size()
or (more importantly) in /proc/sys/fs/pipe-max-size, and then nack nr_slots
in pipe_resize_ring().

So perhaps this check should go into round_pipe_size() ? Although I can't
suggest a simple/clear check without unnecesary restrictions for the case
when pipe_index_t is u16.

pipe_resize_ring() has another caller, watch_queue_set_size(), but it has
its own hard limits...

Oleg.