linux-kernel - [PATCH 4.14 010/159] xfrm: fix rcu usage in xfrm_get_type

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Message-Id: <20180223170744.432128760@linuxfoundation.org>
Date:   Fri, 23 Feb 2018 19:25:18 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        syzbot+ca425f44816d749e8eb49755567a75ee48cf4a30@...kaller.appspotmail.com,
        Sabrina Dubroca <sd@...asysnail.net>,
        Steffen Klassert <steffen.klassert@...unet.com>
Subject: [PATCH 4.14 010/159] xfrm: fix rcu usage in xfrm_get_type_offload

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Sabrina Dubroca <sd@...asysnail.net>

commit 2f10a61cee8fdb9f8da90f5db687e1862b22cf06 upstream.

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>
Signed-off-by: Steffen Klassert <steffen.klassert@...unet.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 net/xfrm/xfrm_state.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/net/xfrm/xfrm_state.c
+++ b/net/xfrm/xfrm_state.c
@@ -313,13 +313,14 @@ retry:
 	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;
 }