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    Subject[PATCH tip/core/urgent 1/3] KEYS: Fix an RCU warning
    Date
    From: David Howells <dhowells@redhat.com>

    Fix the following RCU warning:

    ===================================================
    [ INFO: suspicious rcu_dereference_check() usage. ]
    ---------------------------------------------------
    security/keys/request_key.c:116 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/5372:
    #0: (key_types_sem){.+.+.+}, at: [<ffffffff811a4e3d>] key_type_lookup+0x1c/0x70

    stack backtrace:
    Pid: 5372, comm: keyctl Not tainted 2.6.34-rc3-cachefs #150
    Call Trace:
    [<ffffffff810515f8>] lockdep_rcu_dereference+0xaa/0xb2
    [<ffffffff811a9220>] call_sbin_request_key+0x156/0x2b6
    [<ffffffff811a4c66>] ? __key_instantiate_and_link+0xb1/0xdc
    [<ffffffff811a4cd3>] ? key_instantiate_and_link+0x42/0x5f
    [<ffffffff811a96b8>] ? request_key_auth_new+0x17b/0x1f3
    [<ffffffff811a8e00>] ? request_key_and_link+0x271/0x400
    [<ffffffff810aba6f>] ? kmem_cache_alloc+0xe1/0x118
    [<ffffffff811a8f1a>] request_key_and_link+0x38b/0x400
    [<ffffffff811a7b72>] sys_request_key+0xf7/0x14a
    [<ffffffff81052227>] ? trace_hardirqs_on_caller+0x10c/0x130
    [<ffffffff81393f5c>] ? trace_hardirqs_on_thunk+0x3a/0x3f
    [<ffffffff81001eeb>] system_call_fastpath+0x16/0x1b

    This was caused by doing:

    [root@andromeda ~]# keyctl newring fred @s
    539196288
    [root@andromeda ~]# keyctl request2 user a a 539196288
    request_key: Required key not available

    Signed-off-by: David Howells <dhowells@redhat.com>
    Acked-by: Eric Dumazet <eric.dumazet@gmail.com>
    Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    ---
    security/keys/request_key.c | 13 ++++++++-----
    1 files changed, 8 insertions(+), 5 deletions(-)

    diff --git a/security/keys/request_key.c b/security/keys/request_key.c
    index 03fe63e..ea97c31 100644
    --- a/security/keys/request_key.c
    +++ b/security/keys/request_key.c
    @@ -68,7 +68,8 @@ static int call_sbin_request_key(struct key_construction *cons,
    {
    const struct cred *cred = current_cred();
    key_serial_t prkey, sskey;
    - struct key *key = cons->key, *authkey = cons->authkey, *keyring;
    + struct key *key = cons->key, *authkey = cons->authkey, *keyring,
    + *session;
    char *argv[9], *envp[3], uid_str[12], gid_str[12];
    char key_str[12], keyring_str[3][12];
    char desc[20];
    @@ -112,10 +113,12 @@ static int call_sbin_request_key(struct key_construction *cons,
    if (cred->tgcred->process_keyring)
    prkey = cred->tgcred->process_keyring->serial;

    - if (cred->tgcred->session_keyring)
    - sskey = rcu_dereference(cred->tgcred->session_keyring)->serial;
    - else
    - sskey = cred->user->session_keyring->serial;
    + rcu_read_lock();
    + session = rcu_dereference(cred->tgcred->session_keyring);
    + if (!session)
    + session = cred->user->session_keyring;
    + sskey = session->serial;
    + rcu_read_unlock();

    sprintf(keyring_str[2], "%d", sskey);

    --
    1.7.0


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