[PATCH ipsec] xfrm: fix rcu usage in xfrm_get_type_offload

[Sabrina Dubroca]

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+ca425f44816d749e8eb49755567a75ee48cf4...@syzkaller.appspotmail.com
Signed-off-by: Sabrina Dubroca <s...@queasysnail.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