RDS: Heap OOB write in rds_message_alloc_sgs()

When args->nr_local is 0, nr_pages gets also 0 due some size
calculation via rds_rm_size(), which is later used to allocate
pages for DMA, this bug produces a heap Out-Of-Bound write access
to a specific memory region.

Reported-by: [email protected]
Signed-off-by: Mohamed Ghannam <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

Orabug: 28972461

(cherry picked from commit c095508)
cherry-pick-repo=git/davem/net-next.git

Signed-off-by: Ka-Cheong Poon <[email protected]>
Reviewed-by: Håkon Bugge <[email protected]>
Acked-by: Santosh Shilimkar <[email protected]>

Orabug: 33590097

UEK6 => UEK7

(cherry picked from commit 890b069)
cherry-pick-repo=UEK/production/linux-uek.git

Signed-off-by: Gerd Rausch <[email protected]>
Reviewed-by: William Kucharski <[email protected]>

Author: 0x36

net/rds/rdma.c

@@ -514,6 +514,9 @@ static int rds_rdma_pages(struct rds_rdma_args *args)
 
 	local_vec = (struct rds_iovec __user *)(unsigned long) args->local_vec_addr;
 
+	if (args->nr_local == 0)
+		return -EINVAL;
+
 	/* figure out the number of pages in the vector */
 	for (i = 0; i < args->nr_local; i++) {
 		if (copy_from_user(&vec, &local_vec[i],