linux-kernel - Re: p used before making sure it is not NULL in kernel/auditsc.c

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Message-ID: <20090522040704.GW8633@ZenIV.linux.org.uk>
Date:	Fri, 22 May 2009 05:07:04 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Zhenwen Xu <helight.xu@...il.com>
Cc:	linux-kernel@...r.kernel.org, eparis@...hat.com
Subject: Re: p used before making sure it is not NULL in kernel/auditsc.c

On Fri, May 22, 2009 at 10:22:41AM +0800, Zhenwen Xu wrote:
> p used before making sure it is not NULL in kernel/auditsc.c
> 
> here we should make sure the p is not NULL then use it.

NAK.  ->tree_count can become non-zero only after we had set ->trees
non-NULL.  It's "how much free slots is left in current->trees".
If it's zero, we might have an empty chain (->trees is NULL, we bugger
off and caller tries to allocate) *or* we might be at the end of the
chain (->trees->next is NULL, same as previous) *or* we have more
allocated blocks in the chain, so we move to the next block and
store in there.

As a general note,

	if (foo) {
		...
		dereference p;
		...
	} else if (p) {
		...
		dereference p;
		...
	}

is a perfectly sane code, if foo is true only when p != NULL.
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