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SubjectRe: [PATCH] KEYS: Fix an RCU warning in the reading of user keys
On Wed, Apr 21, 2010 at 05:36:35PM +0100, David Howells wrote:
> Fix an RCU warning in the reading of user keys:
>
> ===================================================
> [ INFO: suspicious rcu_dereference_check() usage. ]
> ---------------------------------------------------
> security/keys/user_defined.c:202 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/3637:
> #0: (&key->sem){+++++.}, at: [<ffffffff811a80ae>] keyctl_read_key+0x9c/0xcf
>
> stack backtrace:
> Pid: 3637, comm: keyctl Not tainted 2.6.34-rc5-cachefs #18
> Call Trace:
> [<ffffffff81051f6c>] lockdep_rcu_dereference+0xaa/0xb2
> [<ffffffff811aa55f>] user_read+0x47/0x91
> [<ffffffff811a80be>] keyctl_read_key+0xac/0xcf
> [<ffffffff811a8a06>] sys_keyctl+0x75/0xb7
> [<ffffffff81001eeb>] system_call_fastpath+0x16/0x1b

Queued for 2.6.34, thank you David!

Thanx, Paul

> Signed-off-by: David Howells <dhowells@redhat.com>
> ---
>
> security/keys/user_defined.c | 3 ++-
> 1 files changed, 2 insertions(+), 1 deletions(-)
>
> diff --git a/security/keys/user_defined.c b/security/keys/user_defined.c
> index 7c687d5..e9aa079 100644
> --- a/security/keys/user_defined.c
> +++ b/security/keys/user_defined.c
> @@ -199,7 +199,8 @@ long user_read(const struct key *key, char __user *buffer, size_t buflen)
> struct user_key_payload *upayload;
> long ret;
>
> - upayload = rcu_dereference(key->payload.data);
> + upayload = rcu_dereference_protected(
> + key->payload.data, rwsem_is_locked(&((struct key *)key)->sem));
> ret = upayload->datalen;
>
> /* we can return the data as is */
>


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