linux-kernel - RE: [PATCH v3 5/5] minmax: Relax check to allow comparison between int and small unsigned constants.

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Message-ID: <de8333e06b0a49d3b18fe9a0be50738c@AcuMS.aculab.com>
Date:   Mon, 14 Aug 2023 14:51:19 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Linus Torvalds' <torvalds@...ux-foundation.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Andy Shevchenko" <andriy.shevchenko@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Christoph Hellwig <hch@...radead.org>,
        "Jason A. Donenfeld" <Jason@...c4.com>
Subject: RE: [PATCH v3 5/5] minmax: Relax check to allow comparison between
 int and small unsigned constants.

From: Linus Torvalds <torvalds@...ux-foundation.org>
> Sent: 10 August 2023 20:47
...
> But using an *unsigned* constant 20 when the other side is signed
> means that now somebody is confused. We should warn.

Then you get 'fixes' like:

int do_tcp_getsockopt(struct sock *sk, int level,
		      int optname, sockptr_t optval, sockptr_t optlen)
{
	struct inet_connection_sock *icsk = inet_csk(sk);
	struct tcp_sock *tp = tcp_sk(sk);
	struct net *net = sock_net(sk);
	int val, len;

	if (copy_from_sockptr(&len, optlen, sizeof(int)))
		return -EFAULT;

	len = min_t(unsigned int, len, sizeof(int));

	if (len < 0)
		return -EINVAL;

(Spotted while looking to see if the generic getsockopt()
code would let now my driver to kernel_getsockopt() on a SCTP
connection to find out the number of streams.
Seems the BPF people haven't yet required the fully generic change.)

	David

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