Commit 2c12ea49 authored May 31, 2012 by Doug Ledford Committed by Linus Torvalds May 31, 2012

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.

[akpm@linux-foundation.org: add a local to simplify overflow-checking expression]
Signed-off-by: Doug Ledford <dledford@redhat.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Manfred Spraul <manfred@colorfullife.com>
Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent d6629859

ipc/mqueue.c

+8 −3

Original line number	Diff line number	Diff line
		@@ -676,6 +676,9 @@ 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;
		unsigned long total_size;

		if (attr->mq_maxmsg <= 0 \|\| attr->mq_msgsize <= 0)
		return 0;
		if (capable(CAP_SYS_RESOURCE)) {
		@@ -690,9 +693,11 @@ 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 *))) <
		(unsigned long)(attr->mq_maxmsg * attr->mq_msgsize))
		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);
		total_size = attr->mq_maxmsg * attr->mq_msgsize;
		if (total_size + mq_treesize < total_size)
		return 0;
		return 1;
		}

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