RDMA/mlx5: Fix integer overflow while resizing CQ

The user can provide very large cqe_size which will cause to integer
overflow as it can be seen in the following UBSAN warning:

=======================================================================
UBSAN: Undefined behaviour in drivers/infiniband/hw/mlx5/cq.c:1192:53
signed integer overflow:
64870 * 65536 cannot be represented in type 'int'
CPU: 0 PID: 267 Comm: syzkaller605279 Not tainted 4.15.0+ #90 Hardware
name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
rel-1.7.5-0-ge51488c-20140602_164612-nilsson.home.kraxel.org 04/01/2014
Call Trace:
 dump_stack+0xde/0x164
 ? dma_virt_map_sg+0x22c/0x22c
 ubsan_epilogue+0xe/0x81
 handle_overflow+0x1f3/0x251
 ? __ubsan_handle_negate_overflow+0x19b/0x19b
 ? lock_acquire+0x440/0x440
 mlx5_ib_resize_cq+0x17e7/0x1e40
 ? cyc2ns_read_end+0x10/0x10
 ? native_read_msr_safe+0x6c/0x9b
 ? cyc2ns_read_end+0x10/0x10
 ? mlx5_ib_modify_cq+0x220/0x220
 ? sched_clock_cpu+0x18/0x200
 ? lookup_get_idr_uobject+0x200/0x200
 ? rdma_lookup_get_uobject+0x145/0x2f0
 ib_uverbs_resize_cq+0x207/0x3e0
 ? ib_uverbs_ex_create_cq+0x250/0x250
 ib_uverbs_write+0x7f9/0xef0
 ? cyc2ns_read_end+0x10/0x10
 ? print_irqtrace_events+0x280/0x280
 ? ib_uverbs_ex_create_cq+0x250/0x250
 ? uverbs_devnode+0x110/0x110
 ? sched_clock_cpu+0x18/0x200
 ? do_raw_spin_trylock+0x100/0x100
 ? __lru_cache_add+0x16e/0x290
 __vfs_write+0x10d/0x700
 ? uverbs_devnode+0x110/0x110
 ? kernel_read+0x170/0x170
 ? sched_clock_cpu+0x18/0x200
 ? security_file_permission+0x93/0x260
 vfs_write+0x1b0/0x550
 SyS_write+0xc7/0x1a0
 ? SyS_read+0x1a0/0x1a0
 ? trace_hardirqs_on_thunk+0x1a/0x1c
 entry_SYSCALL_64_fastpath+0x1e/0x8b
RIP: 0033:0x433549
RSP: 002b:00007ffe63bd1ea8 EFLAGS: 00000217
=======================================================================

Cc: syzkaller <syzkaller@googlegroups.com>
Cc: <stable@vger.kernel.org> # 3.13
Fixes: bde51583 ("IB/mlx5: Add support for resize CQ")
Reported-by: Noa Osherovich <noaos@mellanox.com>
Reviewed-by: Yishai Hadas <yishaih@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/hw/mlx5/cq.c

@@ -1178,7 +1178,12 @@ static int resize_user(struct mlx5_ib_dev *dev, struct mlx5_ib_cq *cq,
 	if (ucmd.reserved0 || ucmd.reserved1)
 		return -EINVAL;
 
-	umem = ib_umem_get(context, ucmd.buf_addr, entries * ucmd.cqe_size,
+	/* check multiplication overflow */
+	if (ucmd.cqe_size && SIZE_MAX / ucmd.cqe_size <= entries - 1)
+		return -EINVAL;
+
+	umem = ib_umem_get(context, ucmd.buf_addr,
+			   (size_t)ucmd.cqe_size * entries,
 			   IB_ACCESS_LOCAL_WRITE, 1);
 	if (IS_ERR(umem)) {
 		err = PTR_ERR(umem);