[PATCH v3] RDMA/core: fix refcount bug in iwpm_get_nlmsg_request()

[Jeffin Philip <jeffinphilip14@gmail.com>]

iwpm_get_nlmsg_request() initializes refcount _after_ list_add_tail()
making it accessible to global list where another CPU can kref_get()
on nlmsg_request causing a refcount "addition on 0" bug. Fix this
by initializing kref _before_ list_add_tail() so refcount for
nlmsg_request can be incremented/decremented normally. In addition,
also initialize every field before list_add_tail().

Reported-by: syzbot+bd317784d628820741b5@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=bd317784d628820741b5
Fixes: 30dc5e63d6a5 ("RDMA/core: Add support for iWARP Port Mapper user space service")
Cc: stable@vger.kernel.org
Signed-off-by: Jeffin Philip <jeffinphilip14@gmail.com>
---
Changelog:
   Changes in v3:
      Sent patch in a new thread and made sure to apply properly.
   Changes in v2:
      Add list_add_tail() last after initializing every field as per Leon Romanovsky's
   suggestion.
---
 drivers/infiniband/core/iwpm_util.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/infiniband/core/iwpm_util.c b/drivers/infiniband/core/iwpm_util.c
index 990cf928b32a..51af8c1c49f9 100644
--- a/drivers/infiniband/core/iwpm_util.c
+++ b/drivers/infiniband/core/iwpm_util.c
@@ -314,10 +314,6 @@ struct iwpm_nlmsg_request *iwpm_get_nlmsg_request(__u32 nlmsg_seq,
 	if (!nlmsg_request)
 		return NULL;
 
-	spin_lock_irqsave(&iwpm_nlmsg_req_lock, flags);
-	list_add_tail(&nlmsg_request->inprocess_list, &iwpm_nlmsg_req_list);
-	spin_unlock_irqrestore(&iwpm_nlmsg_req_lock, flags);
-
 	kref_init(&nlmsg_request->kref);
 	kref_get(&nlmsg_request->kref);
 	nlmsg_request->nlmsg_seq = nlmsg_seq;
@@ -326,6 +322,11 @@ struct iwpm_nlmsg_request *iwpm_get_nlmsg_request(__u32 nlmsg_seq,
 	nlmsg_request->err_code = 0;
 	sema_init(&nlmsg_request->sem, 1);
 	down(&nlmsg_request->sem);
+
+	spin_lock_irqsave(&iwpm_nlmsg_req_lock, flags);
+	list_add_tail(&nlmsg_request->inprocess_list, &iwpm_nlmsg_req_list);
+	spin_unlock_irqrestore(&iwpm_nlmsg_req_lock, flags);
+
 	return nlmsg_request;
 }
 
-- 
2.55.0