netdev - Re: [PATCH] net/sctp: Validate parameter size for SCTP_GET_ASSOC

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Date:	Wed, 27 Feb 2013 15:33:44 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	linux@...ck-us.net
Cc:	netdev@...r.kernel.org, linux-sctp@...r.kernel.org,
	vyasevich@...il.com, sri@...ibm.com, nhorman@...driver.com
Subject: Re: [PATCH] net/sctp: Validate parameter size for
 SCTP_GET_ASSOC_STATS control message

From: Guenter Roeck <linux@...ck-us.net>
Date: Wed, 27 Feb 2013 11:43:51 -0800

> Building sctp may fail with:
> 
> In function ‘copy_from_user’,
>     inlined from ‘sctp_getsockopt_assoc_stats’ at
>     net/sctp/socket.c:5656:20:
> arch/x86/include/asm/uaccess_32.h:211:26: error: call to
>     ‘copy_from_user_overflow’ declared with attribute error: copy_from_user()
>     buffer size is not provably correct
> 
> if built with W=1 due to a missing parameter size validation.
> 
> Signed-off-by: Guenter Roeck <linux@...ck-us.net>

This change is correct, but please fix this by simply moving the:

	/* Allow the struct to grow and fill in as much as possible */
	len = min_t(size_t, len, sizeof(sas));

line higher up in the function.

And I also prefer this because:

	something testing sizeof(foo);
	if (copy_from_user(..., ..., sizeof(foo)))

must easier to audit and validate, especially in patch form.

Otherwise I have to bring the code into an editor and read the whole
function just to make sure you got the type correct.

Thanks.