The command number is not bounds checked against the command mask before it
is shifted, resulting in an ubsan hit. This does not cause malfunction since
the command number is eventually bounds checked, but we can make this ubsan
clean by moving the bounds check to before the mask check.

================================================================================
UBSAN: Undefined behaviour in
drivers/infiniband/core/uverbs_main.c:647:21
shift exponent 207 is too large for 64-bit type 'long long unsigned int'
CPU: 0 PID: 446 Comm: syz-executor3 Not tainted 4.15.0-rc2+ #61
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
__ubsan_handle_shift_out_of_bounds+0x293/0x2f7
? debug_check_no_locks_freed+0x340/0x340
? __ubsan_handle_load_invalid_value+0x19b/0x19b
? lock_acquire+0x440/0x440
? lock_acquire+0x19d/0x440
? __might_fault+0xf4/0x240
? ib_uverbs_write+0x68d/0xe20
ib_uverbs_write+0x68d/0xe20
? __lock_acquire+0xcf7/0x3940
? uverbs_devnode+0x110/0x110
? cyc2ns_read_end+0x10/0x10
? sched_clock_cpu+0x18/0x200
? sched_clock_cpu+0x18/0x200
__vfs_write+0x10d/0x700
? uverbs_devnode+0x110/0x110
? kernel_read+0x170/0x170
? __fget+0x35b/0x5d0
? 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+0x18/0x85
RIP: 0033:0x448e29
RSP: 002b:00007f033f567c58 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f033f5686bc RCX: 0000000000448e29
RDX: 0000000000000060 RSI: 0000000020001000 RDI: 0000000000000012
RBP: 000000000070bea0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000000056a0 R14: 00000000006e8740 R15: 0000000000000000
================================================================================

Cc: syzkaller <syzkaller@googlegroups.com>
Cc: <stable@vger.kernel.org> # 4.5
Fixes: 2dbd5186 ("IB/core: IB/core: Allow legacy verbs through extended interfaces")
Reported-by: Noa Osherovich <noaos@mellanox.com>
Reviewed-by: Matan Barak <matanb@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>