[Patch 2/4] ipc/mqueue: correct mq_attr_ok test

Doug Ledford
2012-05-01T19:08:31Z

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@redhat.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