RDMA/core: Fix use after free in ib_query_qp()

In the Linux kernel, the following vulnerability has been resolved:

RDMA/core: Fix use after free in ib_query_qp()

When querying a QP via the netlink flow the only synchronization
mechanism for the said QP is rdma_restrack_get(), meanwhile during the
QP destroy path rdma_restrack_del() is called at the end of the
ib_destroy_qp_user() function which is too late, since by then the
vendor specific resources for said QP would already be destroyed, and
till the rdma_restrack_del() is called this QP can still be accessed,
which could cause the use after free below.

Fix this by moving the rdma_restrack_begin_del() to the start of the
ib_destroy_qp_user(), which in turn waits for all usages of the QP to be
done then removes it from the database to prevent access to it while it
is being destroyed.

RIP: 0010:ib_query_qp+0x15/0x50 [ib_core]
Code: 48 83 05 5d 8e b9 ff 01 eb b5 66 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 c7 46 40 00 00 00 00 48 c7 46 78 00 00 00 00 <48> 8b 07 48 8b 80 88 01 00 00 48 85 c0 74 1a 48 83 05 54 91 b9 ff
RSP: 0018:ff11000108a8f2f0 EFLAGS: 00010202
RAX: 0000000000000000 RBX: ff11000108a8f370 RCX: ff11000108a8f370
RDX: 0000000000000000 RSI: ff11000108a8f3d8 RDI: 0000000000000000
RBP: ff1100010de5a000 R08: 0000000000000e80 R09: 0000000000000004
R10: ff110001057a604c R11: 0000000000000000 R12: ff11000108a8f370
R13: ff110001090e8000 R14: 0000000000000000 R15: ff110001057a602c
FS: 00007f2ffd8db6c0(0000) GS:ff110008dc90b000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 000000010b9a7004 CR4: 0000000000373eb0
Call Trace:
<TASK>
mlx5_ib_gsi_query_qp+0x21/0x50 [mlx5_ib]
mlx5_ib_query_qp+0x689/0x9d0 [mlx5_ib]
ib_query_qp+0x35/0x50 [ib_core]
fill_res_qp_entry_query.isra.0+0x47/0x280 [ib_core]
? __wake_up+0x40/0x50
? netlink_broadcast_filtered+0x15a/0x550
? kobject_uevent_env+0x562/0x710
? ep_poll_callback+0x242/0x270
? __nla_put+0xc/0x20
? nla_put+0x28/0x40
? nla_put_string+0x2e/0x40 [ib_core]
fill_res_qp_entry+0x138/0x190 [ib_core]
res_get_common_dumpit+0x4a5/0x800 [ib_core]
? fill_res_qp_entry_query.isra.0+0x280/0x280 [ib_core]
nldev_res_get_qp_dumpit+0x1e/0x30 [ib_core]
netlink_dump+0x16f/0x450
__netlink_dump_start+0x1ce/0x2e0
rdma_nl_rcv_msg+0x1d3/0x330 [ib_core]
? nldev_res_get_qp_raw_dumpit+0x30/0x30 [ib_core]
rdma_nl_rcv_skb.constprop.0.isra.0+0x108/0x180 [ib_core]
rdma_nl_rcv+0x12/0x20 [ib_core]
netlink_unicast+0x255/0x380
? __alloc_skb+0xfa/0x1e0
netlink_sendmsg+0x1f3/0x420
__sock_sendmsg+0x38/0x60
____sys_sendmsg+0x1e8/0x230
? copy_msghdr_from_user+0xea/0x170
___sys_sendmsg+0x7c/0xb0
? __futex_wait+0x95/0xf0
? __futex_wake_mark+0x40/0x40
? futex_wait+0x67/0x100
? futex_wake+0xac/0x1b0
__sys_sendmsg+0x5f/0xb0
do_syscall_64+0x55/0xb90
entry_SYSCALL_64_after_hwframe+0x4b/0x53