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

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Date:   Mon, 14 Aug 2023 15:29:46 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     David Laight <David.Laight@...LAB.COM>,
        '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: David Laight
> Sent: 14 August 2023 15:51
>
> 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;

Actually that code has been broken since the test was added in 2.4.4.
At that time min() was a local inline with unsigned int args.
2.4.9 added min(type,a,b)
2.4.10 renamed min() to  min_t() and added min() with the strict
  type checking.

	David

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