netdev - [PATCH ipsec] xfrm: fix rcu usage in xfrm_get_type

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Date:   Sun, 31 Dec 2017 16:18:56 +0100
From:   Sabrina Dubroca <sd@...asysnail.net>
To:     netdev@...r.kernel.org
Cc:     steffen.klassert@...unet.com, syzkaller-bugs@...glegroups.com,
        ilant@...lanox.com,
        syzbot+ca425f44816d749e8eb49755567a75ee48cf4a30@...kaller.appspotmail.com,
        Sabrina Dubroca <sd@...asysnail.net>
Subject: [PATCH ipsec] xfrm: fix rcu usage in xfrm_get_type_offload

request_module can sleep, thus we cannot hold rcu_read_lock() while
calling it. The function also jumps back and takes rcu_read_lock()
again (in xfrm_state_get_afinfo()), resulting in an imbalance.

This codepath is triggered whenever a new offloaded state is created.

Fixes: ffdb5211da1c ("xfrm: Auto-load xfrm offload modules")
Reported-by: syzbot+ca425f44816d749e8eb49755567a75ee48cf4a30@...kaller.appspotmail.com
Signed-off-by: Sabrina Dubroca <sd@...asysnail.net>
---
 net/xfrm/xfrm_state.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c
index 500b3391f474..7e6c297a3924 100644
--- a/net/xfrm/xfrm_state.c
+++ b/net/xfrm/xfrm_state.c
@@ -313,13 +313,14 @@ xfrm_get_type_offload(u8 proto, unsigned short family, bool try_load)
 	if ((type && !try_module_get(type->owner)))
 		type = NULL;
 
+	rcu_read_unlock();
+
 	if (!type && try_load) {
 		request_module("xfrm-offload-%d-%d", family, proto);
 		try_load = 0;
 		goto retry;
 	}
 
-	rcu_read_unlock();
 	return type;
 }
 
-- 
2.15.1