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

Andrew Morton
2012-05-01T19:34:33Z

On Tue, 1 May 2012 13:50:53 -0400
Doug Ledford <dledford@redhat.com> wrote:

> 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).

Please cc Manfred on mqueue things? He still watches ;)

> 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.
>
> ...
>
> --- a/ipc/mqueue.c
> +++ b/ipc/mqueue.c
>
> ...
>
> @@ -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;

That's a bit of a mouthful. Does this look OK?

--- a/ipc/mqueue.c~ipc-mqueue-correct-mq_attr_ok-test-fix
+++ a/ipc/mqueue.c
@@ -672,7 +672,8 @@ static void remove_notification(struct m
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 +691,8 @@ static int mq_attr_ok(struct ipc_namespa
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))
+ total_size = attr->mq_maxmsg * attr->mq_msgsize;
+ if (total_size + mq_treesize < total_size)
return 0;
return 1;
}
_