Code: int rds_rdma_extra_size(struct rds_rdma_args *args)
{
	struct rds_iovec vec;
	struct rds_iovec __user *local_vec;
	int tot_pages = 0;
	unsigned int nr_pages;
	unsigned int i;
 
 	local_vec = (struct rds_iovec __user *)(unsigned long) args->local_vec_addr;
 
 	/* 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],
				   sizeof(struct rds_iovec)))
			return -EFAULT;

		nr_pages = rds_pages_in_vec(&vec);
		if (nr_pages == 0)
			return -EINVAL;

		tot_pages += nr_pages;

		/*
		 * nr_pages for one entry is limited to (UINT_MAX>>PAGE_SHIFT)+1,
		 * so tot_pages cannot overflow without first going negative.
		 */
		if (tot_pages < 0)
			return -EINVAL;
	}

	return tot_pages * sizeof(struct scatterlist);
}

Vulnerability Type: 
CWE ID: CWE-787
Summary: In the Linux kernel through 4.14.13, the rds_message_alloc_sgs() function does not validate a value that is used during DMA page allocation, leading to a heap-based out-of-bounds write (related to the rds_rdma_extra_size function in net/rds/rdma.c).
Commit Message: 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.

Signed-off-by: Mohamed Ghannam <simo.ghannam@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>