[PATCH 29/44] kdbus: Improve tests on incrementing quota

Path	csiph.com!eternal-september.org!feeder.eternal-september.org!aioe.org!bofh.it!news.nic.it!robomod
From	Sergei Zviagintsev <sergei@s15v.net>
Newsgroups	linux.kernel
Subject	[PATCH 29/44] kdbus: Improve tests on incrementing quota
Date	Thu, 08 Oct 2015 13:40:01 +0200
Message-ID	<qhhId-2d4-7@gated-at.bofh.it> (permalink)
References	<qhhId-2d4-3@gated-at.bofh.it>
X-Original-To	Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Daniel Mack <daniel@zonque.org>, David Herrmann <dh.herrmann@googlemail.com>, Djalal Harouni <tixxdz@opendz.org>
Dkim-Signature	v=1; a=rsa-sha1; c=relaxed/relaxed; d=s15v.net; h=cc :date:from:in-reply-to:in-reply-to:message-id:references :references:subject:to:x-sasl-enc:x-sasl-enc; s=mesmtp; bh=IOzIT Qkx+FVoaCflNwP+07HoMOI=; b=yAxjlcAG1fsE2M7C5kBLGgkfq6vfKX7x/6pG9 GD1HYjClGWR8ExuZVTjPAWIHR0fOT8RPvAPqau3sNpU4DO6/iWRMDFMI3YJDXiPH 0xSq7+L8j4fGJBOorqvLeWPCcIvFmXKkEapEoJN818KXfx+t4mKNtmmtSGAVgimL jNrXa4=
Dkim-Signature	v=1; a=rsa-sha1; c=relaxed/relaxed; d= messagingengine.com; h=cc:date:from:in-reply-to:in-reply-to :message-id:references:references:subject:to:x-sasl-enc :x-sasl-enc; s=smtpout; bh=IOzITQkx+FVoaCflNwP+07HoMOI=; b=ix1SL lKmSSPleiTSakr/sTesnKOEsRR4hped0lUeZIKFOt3hhxHhcyAW8IzodEsk1ak7P Tl00FFJjSKrnsuoQuDoPWgoaXAbgq2lIsNiib/Uuqi/5qv50cso+Sgnhhp9VJEo7 zhtwvmIGg7nmSUnwqXUKci50YWMjX2cpYjFbfc=
X-Sasl-Enc	HhaUru57SszS/R/ykqRRjuJlS/bqC8F9qTG/kImEYeV8 1444304042
X-Mailer	git-send-email 1.8.3.1
Sender	robomod@news.nic.it
List-ID	<linux-kernel.vger.kernel.org>
X-Mailing-List	linux-kernel@vger.kernel.org
Approved	robomod@news.nic.it
Lines	69
Organization	linux.* mail to news gateway
X-Original-Cc	linux-kernel@vger.kernel.org, Sergei Zviagintsev <sergei@s15v.net>
X-Original-Date	Thu, 8 Oct 2015 14:31:58 +0300
X-Original-Message-ID	<485d5892acb41541de71031c8d05f70d65a82757.1444302968.git.sergei@s15v.net>
X-Original-References	<cover.1444302968.git.sergei@s15v.net>
X-Original-Sender	linux-kernel-owner@vger.kernel.org
Xref	csiph.com linux.kernel:1242225

Show key headers only | View raw

 - Rewrite

       quota->memory + memory > U32_MAX

   as

       U32_MAX - quota->memory < memory

   There is no overflow issue in the original expression on 32-bit
   because the previous one (available - quota->memory < memory)
   guarantees that quota->memory + memory doesn't exceed `available'
   which is <= U32_MAX in that case. But lets replace it with less
   ambiguous variant.

 - Replace

       quota->fds + fds < quota->fds ||
       quota->fds + fds > KDBUS_CONN_MAX_FDS_PER_USER

   with

       quota->fds > KDBUS_CONN_MAX_FDS_PER_USER ||
       KDBUS_CONN_MAX_FDS_PER_USER - quota->fds < fds

   Reading the code, one can assume that the first original expression
   is there to ensure that quota->fds won't overflow after
   quota->fds += fds, but what it really does is testing for
   size_t overflow in `quota->fds + fds' to be safe in the second
   expression (as fds is size_t, quota->fds is converted to bigger
   type).

   Rewrite it in more obvious way. KDBUS_CONN_MAX_FDS_PER_USER is
   checked at compile time to fill in quota->fds type (there is
   BUILD_BUG_ON), so no further checks for quota->fds overflow are
   needed.

Signed-off-by: Sergei Zviagintsev <sergei@s15v.net>
---
 ipc/kdbus/connection.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/ipc/kdbus/connection.c b/ipc/kdbus/connection.c
index c57ff2c846ee..b32b4f981618 100644
--- a/ipc/kdbus/connection.c
+++ b/ipc/kdbus/connection.c
@@ -717,12 +717,12 @@ int kdbus_conn_quota_inc(struct kdbus_conn *c, struct kdbus_user *u,
 
 	if (available < quota->memory ||
 	    available - quota->memory < memory ||
-	    quota->memory + memory > U32_MAX)
+	    U32_MAX - quota->memory < memory)
 		return -ENOBUFS;
 	if (quota->msgs >= KDBUS_CONN_MAX_MSGS)
 		return -ENOBUFS;
-	if (quota->fds + fds < quota->fds ||
-	    quota->fds + fds > KDBUS_CONN_MAX_FDS_PER_USER)
+	if (quota->fds > KDBUS_CONN_MAX_FDS_PER_USER ||
+	    KDBUS_CONN_MAX_FDS_PER_USER - quota->fds < fds)
 		return -EMFILE;
 
 	quota->memory += memory;
-- 
1.8.3.1

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

Back to linux.kernel | Previous | Next | Find similar | Unroll thread

Thread

[PATCH 29/44] kdbus: Improve tests on incrementing quota Sergei Zviagintsev <sergei@s15v.net> - 2015-10-08 13:40 +0200

csiph-web