netdev - Re: [PATCH] netlink: 2-clause nla

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Message-Id: <20161203.155425.1659260672294542181.davem@davemloft.net>
Date:   Sat, 03 Dec 2016 15:54:25 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     adobriyan@...il.com
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH] netlink: 2-clause nla_ok()

From: Alexey Dobriyan <adobriyan@...il.com>
Date: Fri, 2 Dec 2016 03:59:06 +0300

> nla_ok() consists of 3 clauses:
> 
> 	1) int rem >= (int)sizeof(struct nlattr)
> 
> 	2) u16 nla_len >= sizeof(struct nlattr)
> 
> 	3) u16 nla_len <= int rem
> 
> The statement is that clause (1) is redundant.
> 
> What it does is ensuring that "rem" is a positive number,
> so that in clause (3) positive number will be compared to positive number
> with no problems.
> 
> However, "u16" fully fits into "int" and integers do not change value
> when upcasting even to signed type. Negative integers will be rejected
> by clause (3) just fine. Small positive integers will be rejected
> by transitivity of comparison operator.
> 
> NOTE: all of the above DOES NOT apply to nlmsg_ok() where ->nlmsg_len is
> u32(!), so 3 clauses AND A CAST TO INT are necessary.
> 
> Obligatory space savings report: -1.6 KB
 ...
> Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>

Looks fine, applied to net-next, thanks.