linux-kernel - [PATCH] Fix suspicious RCU usage in nfs_idmap_get

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Date:   Tue,  4 Oct 2016 15:37:40 +0200
From:   Artem Savkov <asavkov@...hat.com>
To:     linux-nfs@...r.kernel.org
Cc:     dhowells@...hat.com, trond.myklebust@...marydata.com,
        anna.schumaker@...app.com, linux-kernel@...r.kernel.org,
        Artem Savkov <asavkov@...hat.com>
Subject: [PATCH] Fix suspicious RCU usage in nfs_idmap_get_key.

nfs_idmap_get_key doesn't hold rkey->sem when calling user_key_payload
resulting in a "suspicious RCU usage" lockdep splat. It does, however hold
rcu_read_lock, so it either needs to use unprotected rcu_dereference, or take
rkey->sem instead of rcu_read_lock.

Signed-off-by: Artem Savkov <asavkov@...hat.com>
---
 fs/nfs/nfs4idmap.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/nfs/nfs4idmap.c b/fs/nfs/nfs4idmap.c
index c444285..a67d1c0 100644
--- a/fs/nfs/nfs4idmap.c
+++ b/fs/nfs/nfs4idmap.c
@@ -309,7 +309,7 @@ static ssize_t nfs_idmap_get_key(const char *name, size_t namelen,
 		goto out;
 	}
 
-	rcu_read_lock();
+	down_read(&rkey->sem);
 	rkey->perm |= KEY_USR_VIEW;
 
 	ret = key_validate(rkey);
@@ -329,7 +329,7 @@ static ssize_t nfs_idmap_get_key(const char *name, size_t namelen,
 		ret = -EINVAL;
 
 out_up:
-	rcu_read_unlock();
+	up_read(&rkey->sem);
 	key_put(rkey);
 out:
 	return ret;
-- 
2.7.4