linux-kernel - [PATCH] KEYS: Don't need to use RCU in keyring

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Message-ID: <20100324091039.29436.17207.stgit@warthog.procyon.org.uk>
Date:	Wed, 24 Mar 2010 09:10:39 +0000
From:	David Howells <dhowells@...hat.com>
To:	torvalds@...l.org, akpm@...ux-foundation.org
Cc:	paulmck@...ux.vnet.ibm.com, linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org, David Howells <dhowells@...hat.com>
Subject: [PATCH] KEYS: Don't need to use RCU in keyring_read() as semaphore is
	held

keyring_read() doesn't need to use rcu_dereference() to access the keyring
payload as the caller holds the key semaphore to prevent modifications from
happening whilst the data is read out.

This should solve the following warning:

===================================================
[ INFO: suspicious rcu_dereference_check() usage. ]
---------------------------------------------------
security/keys/keyring.c:204 invoked rcu_dereference_check() without protection!

other info that might help us debug this:


rcu_scheduler_active = 1, debug_locks = 0
1 lock held by keyctl/2144:
 #0:  (&key->sem){+++++.}, at: [<ffffffff81177f7c>] keyctl_read_key+0x9c/0xcf

stack backtrace:
Pid: 2144, comm: keyctl Not tainted 2.6.34-rc2-cachefs #113
Call Trace:
 [<ffffffff8105121f>] lockdep_rcu_dereference+0xaa/0xb2
 [<ffffffff811762d5>] keyring_read+0x4d/0xe7
 [<ffffffff81177f8c>] keyctl_read_key+0xac/0xcf
 [<ffffffff811788d4>] sys_keyctl+0x75/0xb9
 [<ffffffff81001eeb>] system_call_fastpath+0x16/0x1b

Signed-off-by: David Howells <dhowells@...hat.com>
---

 security/keys/keyring.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/security/keys/keyring.c b/security/keys/keyring.c
index 840be66..8fa2df0 100644
--- a/security/keys/keyring.c
+++ b/security/keys/keyring.c
@@ -201,7 +201,7 @@ static long keyring_read(const struct key *keyring,
 	int loop, ret;
 
 	ret = 0;
-	klist = rcu_dereference(keyring->payload.subscriptions);
+	klist = keyring->payload.subscriptions;
 
 	if (klist) {
 		/* calculate how much data we could return */

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