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    Subject[PATCH v27 20/25] LSM: Verify LSM display sanity in binder
    Date
    Verify that the tasks on the ends of a binder transaction
    use the same "interface_lsm" security module. This prevents
    confusion of security "contexts".

    Reviewed-by: Kees Cook <keescook@chromium.org>
    Reviewed-by: John Johansen <john.johansen@canonical.com>
    Acked-by: Stephen Smalley <sds@tycho.nsa.gov>
    Acked-by: Paul Moore <paul@paul-moore.com>
    Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
    ---
    security/security.c | 29 +++++++++++++++++++++++++++++
    1 file changed, 29 insertions(+)

    diff --git a/security/security.c b/security/security.c
    index a5150de2f3db..ae23b5a8fe87 100644
    --- a/security/security.c
    +++ b/security/security.c
    @@ -859,9 +859,38 @@ int security_binder_set_context_mgr(struct task_struct *mgr)
    return call_int_hook(binder_set_context_mgr, 0, mgr);
    }

    +/**
    + * security_binder_transaction - Binder driver transaction check
    + * @from: source of the transaction
    + * @to: destination of the transaction
    + *
    + * Verify that the tasks have the same LSM "display", then
    + * call the security module hooks.
    + *
    + * Returns -EINVAL if the displays don't match, or the
    + * result of the security module checks.
    + */
    int security_binder_transaction(struct task_struct *from,
    struct task_struct *to)
    {
    + int from_ilsm = lsm_task_ilsm(from);
    + int to_ilsm = lsm_task_ilsm(to);
    +
    + /*
    + * If the ilsm is LSMBLOB_INVALID the first module that has
    + * an entry is used. This will be in the 0 slot.
    + *
    + * This is currently only required if the server has requested
    + * peer contexts, but it would be unwieldly to have too much of
    + * the binder driver detail here.
    + */
    + if (from_ilsm == LSMBLOB_INVALID)
    + from_ilsm = 0;
    + if (to_ilsm == LSMBLOB_INVALID)
    + to_ilsm = 0;
    + if (from_ilsm != to_ilsm)
    + return -EINVAL;
    +
    return call_int_hook(binder_transaction, 0, from, to);
    }

    --
    2.29.2
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