From: "Theodore Ts'o" <tytso@mit.edu>
To: Hannes Frederic Sowa <hannes@stressinduktion.org>
Cc: Dave Jones <davej@redhat.com>,
Linux Kernel <linux-kernel@vger.kernel.org>,
Greg Price <price@mit.edu>
Subject: Re: [PATCH] random: check for increase of entropy_count because of signed conversion
Date: Fri, 18 Jul 2014 17:25:04 -0400 [thread overview]
Message-ID: <20140718212504.GC18775@thunk.org> (raw)
In-Reply-To: <442eeebeb78f9f2d4066ad923f4144fc2110c6f7.1405538086.git.hannes@stressinduktion.org>
On Wed, Jul 16, 2014 at 09:18:15PM +0200, Hannes Frederic Sowa wrote:
> The expression entropy_count -= ibytes << (ENTROPY_SHIFT + 3) could
> actually increase entropy_count if during assignment of the unsigned
> expression on the RHS (mind the -=) we reduce the value modulo
> 2^width(int) and assign it to entropy_count. Trinity found this.
>
> Reported-by: Dave Jones <davej@redhat.com>
> Cc: Theodore Ts'o <tytso@mit.edu>
> Cc: Greg Price <price@mit.edu>
> Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
> ---
> As indicated by credit_entropy_bits entropy_count cannot get negative,
> so I don't see any reason to include a check for entropy_count < 0
> here. Do you agree?
No, the check is important; after we subtract ibytes << (ENTROPY_SHIFT
+ 3) we could drive entropy_count negative, and we don't want to
trigger the WARN_ON().
I'll modify the patch to keep the check.
- Ted
next prev parent reply other threads:[~2014-07-18 21:25 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-05-12 15:42 perf: use after free in perf_remove_from_context Sasha Levin
2014-05-14 16:29 ` Peter Zijlstra
2014-05-14 16:32 ` Sasha Levin
2014-05-14 16:35 ` Peter Zijlstra
2014-05-14 16:38 ` Sasha Levin
2014-05-14 16:52 ` Peter Zijlstra
2014-05-14 17:09 ` Sasha Levin
2014-05-14 17:20 ` Dave Jones
2014-05-14 18:37 ` Peter Zijlstra
2014-05-28 23:52 ` Sasha Levin
2014-05-29 2:31 ` Sasha Levin
2014-05-29 7:59 ` Peter Zijlstra
2014-05-29 7:57 ` Peter Zijlstra
2014-05-29 14:47 ` Sasha Levin
2014-05-29 15:07 ` Peter Zijlstra
2014-05-29 16:44 ` Sasha Levin
2014-05-29 16:50 ` Peter Zijlstra
2014-05-29 16:52 ` Sasha Levin
2014-05-29 17:00 ` Peter Zijlstra
2014-05-29 22:37 ` Sasha Levin
2014-06-05 14:38 ` [tip:perf/core] perf: Fix use after free in perf_remove_from_context() tip-bot for Peter Zijlstra
2014-05-15 18:11 ` eventpoll __list_del_entry corruption (was: perf: use after free in perf_remove_from_context) Peter Zijlstra
2014-05-15 18:16 ` eventpoll __list_del_entry corruption Sasha Levin
2014-06-16 9:44 ` Eric Wong
2014-05-21 8:25 ` BUG at /usr/src/linux-2.6/mm/filemap.c:202 (was: perf: use after free in perf_remove_from_context) Peter Zijlstra
2014-05-21 13:02 ` BUG at /usr/src/linux-2.6/mm/filemap.c:202 Sasha Levin
2014-06-03 15:07 ` eventpoll __list_del_entry corruption Jason Baron
2014-06-03 15:11 ` Peter Zijlstra
2014-05-16 15:34 ` BUG_ON drivers/char/random.c:986 (Was: perf: use after free in perf_remove_from_context) Peter Zijlstra
2014-05-16 16:06 ` H. Peter Anvin
2014-05-16 16:21 ` Peter Zijlstra
2014-05-17 0:46 ` Hannes Frederic Sowa
2014-05-17 2:18 ` Theodore Ts'o
2014-05-17 16:24 ` Sasha Levin
2014-05-17 17:00 ` Peter Zijlstra
2014-07-15 4:36 ` BUG_ON drivers/char/random.c:986 Dave Jones
2014-07-15 20:29 ` Hannes Frederic Sowa
2014-07-16 8:33 ` Theodore Ts'o
2014-07-16 19:18 ` [PATCH] random: check for increase of entropy_count because of signed conversion Hannes Frederic Sowa
2014-07-18 21:25 ` Theodore Ts'o [this message]
2014-07-18 21:43 ` Hannes Frederic Sowa
2014-07-18 21:50 ` Theodore Ts'o
2014-07-18 22:07 ` Theodore Ts'o
2014-07-18 23:35 ` Hannes Frederic Sowa
2014-07-19 5:42 ` Theodore Ts'o
2014-07-19 6:20 ` Hannes Frederic Sowa
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