[PATCH] RDMA/rxe: fix possible NULL MR dereference

[Li Zhijian]

Daisuke mentioned that:
If responder get a zero-byte RDMA Read request, qp->resp.mr
is not set in check_rkey(). The mr is NULL in this case, and a NULL pointer
dereference occurs as shown below.

 BUG: kernel NULL pointer dereference, address: 0000000000000010
 #PF: supervisor write access in kernel mode
 #PF: error_code(0x0002) - not-present page
 PGD 0 P4D 0
 Oops: 0002 [#1] PREEMPT SMP PTI
 CPU: 2 PID: 3622 Comm: python3 Kdump: loaded Not tainted 6.1.0-rc3+ #34
 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014
 RIP: 0010:__rxe_put+0xc/0x60 [rdma_rxe]
 Code: cc cc cc 31 f6 e8 64 36 1b d3 41 b8 01 00 00 00 44 89 c0 c3 cc cc cc cc 41 89 c0 eb c1 90 0f 1f 44 00 00 41 54 b8 ff ff ff ff <f0> 0f c1 47 10 83 f8 01 74 11 45 31 e4 85 c0 7e 20 44 89 e0 41 5c
 RSP: 0018:ffffb27bc012ce78 EFLAGS: 00010246
 RAX: 00000000ffffffff RBX: ffff9790857b0580 RCX: 0000000000000000
 RDX: ffff979080fe145a RSI: 000055560e3e0000 RDI: 0000000000000000
 RBP: ffff97909c7dd800 R08: 0000000000000001 R09: e7ce43d97f7bed0f
 R10: ffff97908b29c300 R11: 0000000000000000 R12: 0000000000000000
 R13: 0000000000000000 R14: ffff97908b29c300 R15: 0000000000000000
 FS:  00007f276f7bd740(0000) GS:ffff9792b5c80000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 0000000000000010 CR3: 0000000114230002 CR4: 0000000000060ee0
 Call Trace:
  <IRQ>
  read_reply+0xda/0x310 [rdma_rxe]
  rxe_responder+0x82d/0xe50 [rdma_rxe]
  do_task+0x84/0x170 [rdma_rxe]
  tasklet_action_common.constprop.0+0xa7/0x120
  __do_softirq+0xcb/0x2ac
  do_softirq+0x63/0x90
  </IRQ>

Test mr before dereference it to avoid this problem.

Fixes: b5f9a01fae42 ("RDMA/rxe: Fix mr leak in RESPST_ERR_RNR")
Reported-by: Daisuke Matsuda <matsuda-daisuke@xxxxxxxxxxx>
Signed-off-by: Li Zhijian <lizhijian@xxxxxxxxxxx>
---
Hope we can catch up with 6.1
---
 drivers/infiniband/sw/rxe/rxe_resp.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/infiniband/sw/rxe/rxe_resp.c b/drivers/infiniband/sw/rxe/rxe_resp.c
index 693081e813ec..bbb9665c64ad 100644
--- a/drivers/infiniband/sw/rxe/rxe_resp.c
+++ b/drivers/infiniband/sw/rxe/rxe_resp.c
@@ -807,7 +807,8 @@ static enum resp_states read_reply(struct rxe_qp *qp,
 	skb = prepare_ack_packet(qp, &ack_pkt, opcode, payload,
 				 res->cur_psn, AETH_ACK_UNLIMITED);
 	if (!skb) {
-		rxe_put(mr);
+		if (mr)
+			rxe_put(mr);
 		return RESPST_ERR_RNR;
 	}
 
-- 
2.38.1