linux-kernel - Re: [PATCH] radix_tree_tag_get() is not as safe as the docs make out

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Date:	Tue, 06 Apr 2010 22:18:58 +0100
From:	David Howells <dhowells@...hat.com>
To:	Nick Piggin <npiggin@...e.de>
Cc:	dhowells@...hat.com, torvalds@...l.org, akpm@...ux-foundation.org,
	paulmck@...ux.vnet.ibm.com, corbet@....net,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH] radix_tree_tag_get() is not as safe as the docs make out

Nick Piggin <npiggin@...e.de> wrote:

> Nack, just drop the BUG_ON.

I can do that.

> I don't know what you mean by "untrustworthy answer".

I was thinking that the answer you get from radix_tree_tag_get() may be invalid
if the tag chain is being modified as you read it.  So if you do:

	rcu_read_lock()
	...
	x = radix_tree_tag_get(r, i, t);
	...
	y = radix_tree_tag_get(r, i, t);
	...
	rcu_read_unlock()

Then you can't guarantee that x == y, even though you were holding the RCU read
lock.

As you suggested, I'll try and come up with a comment modification to this
effect.

David
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/