[PATCH] rpcrdma: don't decref EP if a ESTABLISHED did not happen

[Dan Aloni <dan.aloni@vastdata.com>]

We found a case where `RDMA_CM_EVENT_DEVICE_REMOVAL` causes a refcount
underflow.

The specific scenario that caused this to happen is IB device bonding,
when bringing down one of the ports, or all ports. The situation is not
just a print - it also causes a non-recoverable state it is not even
possible to complete the disconnect and shut it down the mount,
requiring a reboot, suggesting that tear-down is also incomplete in this
state.

The trivial fix seems to work as such - if we did not receive a
`RDMA_CM_EVENT_ESTABLISHED`, we should not decref the EP, otherwise
`rpcrdma_xprt_drain` kills the EP prematurely in from the context of
`rpcrdma_xprt_disconnect`.

Fixes: 2acc5cae2923 ('xprtrdma: Prevent dereferencing r_xprt->rx_ep after it is freed')

Example crash:

rpcrdma: removing device mlx5_3 for 172.21.208.2:20049
------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: CPU: 60 PID: 19700 at lib/refcount.c:28 refcount_warn_saturate+0xba/0x110
Modules linked in: mst_pciconf(OE) nfsv3(OE) nfs_acl(OE) rpcsec_gss_krb5(OE) auth_rpcgss(OE) nfsv4(OE) dns_resolver rpcrdma(OE) nfs(OE) lockd(OE) grace compat_nfs_ssc(OE) snd_seq_dummy snd_hrtimer snd_seq snd_timer snd_seq_device snd soundcore uio_pci_generic uio vfio_pci vfio_pci_core vfio_virqfd vfio_iommu_>
isst_if_mmio mei isst_if_common i2c_smbus intel_pch_thermal intel_vsec ipmi_msghandler acpi_power_meter xfs libcrc32c mlx5_ib(OE) ib_uverbs(OE) ib_core(OE) sd_mod t10_pi sg mgag200 i2c_algo_bit drm_shmem_helper drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops ahci libahci drm crct10dif_pclmul mlx>
CPU: 60 PID: 19700 Comm: kworker/u132:4 Kdump: loaded Tainted: G        W  OE    --------  ---  5.14.0-284.11.1.el9_2.x86_64 #1
Hardware name: Dell Inc. PowerEdge C6520/0TY3YW, BIOS 1.8.2 09/14/2022
Workqueue: xprtiod xprt_rdma_connect_worker [rpcrdma]
RIP: 0010:refcount_warn_saturate+0xba/0x110
Code: 01 01 e8 27 e1 56 00 0f 0b c3 cc cc cc cc 80 3d b8 29 9b 01 00 75 85 48 c7 c7 38 ec 04 93 c6 05 a8 29 9b 01 01 e8 04 e1 56 00 <0f> 0b c3 cc cc cc cc 80 3d 93 29 9b 01 00 0f 85 5e ff ff ff 48 c7
RSP: 0018:ff34fa4968cafe10 EFLAGS: 00010282
RAX: 0000000000000000 RBX: ff1210404a15e000 RCX: 0000000000000027
RDX: ff12103f803998a8 RSI: 0000000000000001 RDI: ff12103f803998a0
RBP: ff1210404a15e648 R08: 0000000000000000 R09: 00000000ffff7fff
R10: ff34fa4968cafcb0 R11: ffffffff939e9608 R12: 0000000000000000
R13: dead000000000122 R14: dead000000000100 R15: ff1210404a15e928
FS:  0000000000000000(0000) GS:ff12103f80380000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f170f8a5000 CR3: 00000001c3adc002 CR4: 0000000000771ee0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
PKRU: 55555554
Call Trace:
<TASK>
rpcrdma_ep_put+0x42/0x50 [rpcrdma]
rpcrdma_xprt_disconnect+0x303/0x3b0 [rpcrdma]
xprt_rdma_connect_worker+0xc8/0xd0 [rpcrdma]
process_one_work+0x1e5/0x3c0
? rescuer_thread+0x3a0/0x3a0
worker_thread+0x50/0x3b0
? rescuer_thread+0x3a0/0x3a0
kthread+0xd6/0x100
? kthread_complete_and_exit+0x20/0x20
ret_from_fork+0x1f/0x30
</TASK>

Signed-off-by: Dan Aloni <dan.aloni@vastdata.com>
---
 net/sunrpc/xprtrdma/verbs.c     | 5 ++++-
 net/sunrpc/xprtrdma/xprt_rdma.h | 1 +
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/net/sunrpc/xprtrdma/verbs.c b/net/sunrpc/xprtrdma/verbs.c
index 4f8d7efa469f..19996515da94 100644
--- a/net/sunrpc/xprtrdma/verbs.c
+++ b/net/sunrpc/xprtrdma/verbs.c
@@ -250,6 +250,7 @@ rpcrdma_cm_event_handler(struct rdma_cm_id *id, struct rdma_cm_event *event)
 		goto disconnected;
 	case RDMA_CM_EVENT_ESTABLISHED:
 		rpcrdma_ep_get(ep);
+               ep->re_connect_ref = true;
 		ep->re_connect_status = 1;
 		rpcrdma_update_cm_private(ep, &event->param.conn);
 		trace_xprtrdma_inline_thresh(ep);
@@ -272,7 +273,9 @@ rpcrdma_cm_event_handler(struct rdma_cm_id *id, struct rdma_cm_event *event)
 		ep->re_connect_status = -ECONNABORTED;
 disconnected:
 		rpcrdma_force_disconnect(ep);
-		return rpcrdma_ep_put(ep);
+		if (ep->re_connect_ref)
+			return rpcrdma_ep_put(ep);
+		return 0;
 	default:
 		break;
 	}
diff --git a/net/sunrpc/xprtrdma/xprt_rdma.h b/net/sunrpc/xprtrdma/xprt_rdma.h
index da409450dfc0..1553ef69a844 100644
--- a/net/sunrpc/xprtrdma/xprt_rdma.h
+++ b/net/sunrpc/xprtrdma/xprt_rdma.h
@@ -84,6 +84,7 @@ struct rpcrdma_ep {
 	unsigned int		re_max_inline_recv;
 	int			re_async_rc;
 	int			re_connect_status;
+	bool			re_connect_ref;
 	atomic_t		re_receiving;
 	atomic_t		re_force_disconnect;
 	struct ib_qp_init_attr	re_attr;
-- 
2.39.3