RE: [PATCH] usb: host: add cast to avoid potential integer overflow

From	David Laight <David.Laight@ACULAB.COM>
Newsgroups	linux.kernel
Subject	RE: [PATCH] usb: host: add cast to avoid potential integer overflow
Date	2017-02-20 13:50 +0100
Message-ID	<tcVzI-4Iy-17@gated-at.bofh.it> (permalink)
References	<tbErg-5k2-3@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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From: Gustavo A. R. Silva
> Sent: 17 February 2017 00:17
> The type of variable 'sel' is unsigned int. Such variable is being used
> multiple times in a context that expects an expression of type unsigned
> long long. So, to avoid any potential integer overflow, a cast to type
> unsigned long long is added.
...
> -		timeout_ns = udev->u1_params.sel * 3;
> +		timeout_ns = (unsigned long long)udev->u1_params.sel * 3;
...

It is probably better to just change the constant to 3ull.
However I'd be tempted to look more closely at the valid values
for 'timeout_ns'.
It seems unlikely that that the timeout (in sel) will be near
enough to 4 seconds that multiplying by a small integer will
take the value over 4 seconds without requiring larger input
values be supported.

timeout_ns might even be being used in places where the value
has to be smaller than 1 second!

	David

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[PATCH] usb: host: add cast to avoid potential integer overflow "Gustavo A. R. Silva" <garsilva@embeddedor.com> - 2017-02-17 01:20 +0100
  RE: [PATCH] usb: host: add cast to avoid potential integer overflow David Laight <David.Laight@ACULAB.COM> - 2017-02-20 13:50 +0100

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