Fix NULL pointer dereference in the error flow of ib_create_qp_user
when accessing to uninitialized list pointers - rdma_mrs and sig_mrs.
The following crash from syzkaller revealed it.

  kasan: GPF could be caused by NULL-ptr deref or user memory access
  general protection fault: 0000 [#1] SMP KASAN PTI
  CPU: 1 PID: 23167 Comm: syz-executor.1 Not tainted 5.5.0-rc5 #2
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
  rel-1.12.1-0-ga5cab58e9a3f-prebuilt.qemu.org 04/01/2014
  RIP: 0010:ib_mr_pool_destroy+0x81/0x1f0
  Code: 00 00 fc ff df 49 c1 ec 03 4d 01 fc e8 a8 ea 72 fe 41 80 3c 24 00
  0f 85 62 01 00 00 48 8b 13 48 89 d6 4c 8d 6a c8 48 c1 ee 03 <42> 80 3c
  3e 00 0f 85 34 01 00 00 48 8d 7a 08 4c 8b 02 48 89 fe 48
  RSP: 0018:ffffc9000951f8b0 EFLAGS: 00010046
  RAX: 0000000000040000 RBX: ffff88810f268038 RCX: ffffffff82c41628
  RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffc9000951f850
  RBP: ffff88810f268020 R08: 0000000000000004 R09: fffff520012a3f0a
  R10: 0000000000000001 R11: fffff520012a3f0a R12: ffffed1021e4d007
  R13: ffffffffffffffc8 R14: 0000000000000246 R15: dffffc0000000000
  FS:  00007f54bc788700(0000) GS:ffff88811b100000(0000)
  knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 0000000000000000 CR3: 0000000116920002 CR4: 0000000000360ee0
  DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
  DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
  Call Trace:
   rdma_rw_cleanup_mrs+0x15/0x30
   ib_destroy_qp_user+0x674/0x7d0
   ib_create_qp_user+0xb01/0x11c0
   create_qp+0x1517/0x2130
   ib_uverbs_create_qp+0x13e/0x190
   ib_uverbs_write+0xaa5/0xdf0
   __vfs_write+0x7c/0x100
   vfs_write+0x168/0x4a0
   ksys_write+0xc8/0x200
   do_syscall_64+0x9c/0x390
   entry_SYSCALL_64_after_hwframe+0x44/0xa9
  RIP: 0033:0x465b49
  Code: f7 d8 64 89 02 b8 ff ff ff ff c3 66 0f 1f 44 00 00 48 89 f8 48 89
  f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01
  f0 ff ff 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48
  RSP: 002b:00007f54bc787c58 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
  RAX: ffffffffffffffda RBX: 000000000073bf00 RCX: 0000000000465b49
  RDX: 0000000000000040 RSI: 0000000020000540 RDI: 0000000000000003
  RBP: 00007f54bc787c70 R08: 0000000000000000 R09: 0000000000000000
  R10: 0000000000000000 R11: 0000000000000246 R12: 00007f54bc7886bc
  R13: 00000000004ca2ec R14: 000000000070ded0 R15: 0000000000000005

Fixes: a060b562 ("IB/core: generic RDMA READ/WRITE API")
Link: https://lore.kernel.org/r/20200227112708.93023-1-leon@kernel.orgSigned-off-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>