linux-kernel - [Patch 2/4] ipc/mqueue: correct mq_attr

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Date:	Tue,  1 May 2012 13:50:53 -0400
From:	Doug Ledford <dledford@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	akpm@...ux-foundation.org, sfr@...b.auug.org.au,
	Doug Ledford <dledford@...hat.com>
Subject: [Patch 2/4] ipc/mqueue: correct mq_attr_ok test

While working on the other parts of the mqueue stuff, I noticed that
the calculation for overflow in mq_attr_ok didn't actually match
reality (this is especially true since my last patch which changed
how we account memory slightly).

In particular, we used to test for overflow using:
  msgs * msgsize + msgs * sizeof(struct msg_msg *)

That was never really correct because each message we allocate via
load_msg() is actually a struct msg_msg followed by the data for
the message (and if struct msg_msg + data exceeds PAGE_SIZE we end
up allocating struct msg_msgseg structs too, but accounting for them
would get really tedious, so let's ignore those...they're only a
pointer in size anyway).  This patch updates the calculation to be
more accurate in regards to maximum possible memory consumption by the
mqueue.

Signed-off-by: Doug Ledford <dledford@...hat.com>
---
 ipc/mqueue.c |    9 +++++++--
 1 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/ipc/mqueue.c b/ipc/mqueue.c
index fd49cfc..4b2892e 100644
--- a/ipc/mqueue.c
+++ b/ipc/mqueue.c
@@ -670,6 +670,8 @@ static void remove_notification(struct mqueue_inode_info *info)
 
 static int mq_attr_ok(struct ipc_namespace *ipc_ns, struct mq_attr *attr)
 {
+	int mq_treesize;
+
 	if (attr->mq_maxmsg <= 0 || attr->mq_msgsize <= 0)
 		return 0;
 	if (capable(CAP_SYS_RESOURCE)) {
@@ -684,8 +686,11 @@ static int mq_attr_ok(struct ipc_namespace *ipc_ns, struct mq_attr *attr)
 	/* check for overflow */
 	if (attr->mq_msgsize > ULONG_MAX/attr->mq_maxmsg)
 		return 0;
-	if ((unsigned long)(attr->mq_maxmsg * (attr->mq_msgsize
-	    + sizeof (struct msg_msg *))) <
+	mq_treesize = attr->mq_maxmsg * sizeof(struct msg_msg) +
+		min_t(unsigned int, attr->mq_maxmsg, MQ_PRIO_MAX) *
+		sizeof(struct posix_msg_tree_node);
+	if ((unsigned long)(attr->mq_maxmsg * attr->mq_msgsize +
+			    mq_treesize) <
 	    (unsigned long)(attr->mq_maxmsg * attr->mq_msgsize))
 		return 0;
 	return 1;
-- 
1.7.7.6

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