RDMA/uverbs: Sanitize user entered port numbers prior to access it

==================================================================
BUG: KASAN: use-after-free in copy_ah_attr_from_uverbs+0x6f2/0x8c0
Read of size 4 at addr ffff88006476a198 by task syzkaller697701/265

CPU: 0 PID: 265 Comm: syzkaller697701 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
 ? show_regs_print_info+0x17/0x17
 ? lock_contended+0x11a0/0x11a0
 print_address_description+0x83/0x3e0
 kasan_report+0x18c/0x4b0
 ? copy_ah_attr_from_uverbs+0x6f2/0x8c0
 ? copy_ah_attr_from_uverbs+0x6f2/0x8c0
 ? lookup_get_idr_uobject+0x120/0x200
 ? copy_ah_attr_from_uverbs+0x6f2/0x8c0
 copy_ah_attr_from_uverbs+0x6f2/0x8c0
 ? modify_qp+0xd0e/0x1350
 modify_qp+0xd0e/0x1350
 ib_uverbs_modify_qp+0xf9/0x170
 ? ib_uverbs_query_qp+0xa70/0xa70
 ib_uverbs_write+0x7f9/0xef0
 ? attach_entity_load_avg+0x8b0/0x8b0
 ? ib_uverbs_query_qp+0xa70/0xa70
 ? uverbs_devnode+0x110/0x110
 ? cyc2ns_read_end+0x10/0x10
 ? print_irqtrace_events+0x280/0x280
 ? sched_clock_cpu+0x18/0x200
 ? _raw_spin_unlock_irq+0x29/0x40
 ? _raw_spin_unlock_irq+0x29/0x40
 ? _raw_spin_unlock_irq+0x29/0x40
 ? time_hardirqs_on+0x27/0x670
 __vfs_write+0x10d/0x700
 ? uverbs_devnode+0x110/0x110
 ? kernel_read+0x170/0x170
 ? _raw_spin_unlock_irq+0x29/0x40
 ? finish_task_switch+0x1bd/0x7a0
 ? finish_task_switch+0x194/0x7a0
 ? prandom_u32_state+0xe/0x180
 ? rcu_read_unlock+0x80/0x80
 ? 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: 0033:0x433c29
RSP: 002b:00007ffcf2be82a8 EFLAGS: 00000217

Allocated by task 62:
 kasan_kmalloc+0xa0/0xd0
 kmem_cache_alloc+0x141/0x480
 dup_fd+0x101/0xcc0
 copy_process.part.62+0x166f/0x4390
 _do_fork+0x1cb/0xe90
 kernel_thread+0x34/0x40
 call_usermodehelper_exec_work+0x112/0x260
 process_one_work+0x929/0x1aa0
 worker_thread+0x5c6/0x12a0
 kthread+0x346/0x510
 ret_from_fork+0x3a/0x50

Freed by task 259:
 kasan_slab_free+0x71/0xc0
 kmem_cache_free+0xf3/0x4c0
 put_files_struct+0x225/0x2c0
 exit_files+0x88/0xc0
 do_exit+0x67c/0x1520
 do_group_exit+0xe8/0x380
 SyS_exit_group+0x1e/0x20
 entry_SYSCALL_64_fastpath+0x1e/0x8b

The buggy address belongs to the object at ffff88006476a000
 which belongs to the cache files_cache of size 832
The buggy address is located 408 bytes inside of
 832-byte region [ffff88006476a000, ffff88006476a340)
The buggy address belongs to the page:
page:ffffea000191da80 count:1 mapcount:0 mapping:          (null) index:0x0 compound_mapcount: 0
flags: 0x4000000000008100(slab|head)
raw: 4000000000008100 0000000000000000 0000000000000000 0000000100080008
raw: 0000000000000000 0000000100000001 ffff88006bcf7a80 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88006476a080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88006476a100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88006476a180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                            ^
 ffff88006476a200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88006476a280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Cc: syzkaller <syzkaller@googlegroups.com>
Cc: <stable@vger.kernel.org> # 4.11
Fixes: 44c58487 ("IB/core: Define 'ib' and 'roce' rdma_ah_attr types")
Reported-by: Noa Osherovich <noaos@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>