linux-kernel - Re: [PATCH v2 1/4] fs/pipe: Limit the slots in pipe_resize

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Message-ID: <20250307145125.GE5963@redhat.com>
Date: Fri, 7 Mar 2025 15:51:25 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: K Prateek Nayak <kprateek.nayak@....com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Jan Kara <jack@...e.cz>,
	"Matthew Wilcox (Oracle)" <willy@...radead.org>,
	Mateusz Guzik <mjguzik@...il.com>,
	Rasmus Villemoes <ravi@...vas.dk>,
	"Gautham R. Shenoy" <gautham.shenoy@....com>,
	Neeraj.Upadhyay@....com, Ananth.narayan@....com,
	Swapnil Sapkal <swapnil.sapkal@....com>
Subject: Re: [PATCH v2 1/4] fs/pipe: Limit the slots in pipe_resize_ring()

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@...hat.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.