Re: [PATCH v19 19/23] LSM: Verify LSM display sanity in binder

Verify that the tasks on the ends of a binder transaction use the same "display" security module. This prevents confusion of security "contexts".

Reviewed-by: Kees Cook <keescook(a)chromium.org&gt; Acked-by: Stephen Smalley <sds(a)tycho.nsa.gov&gt; Signed-off-by: Casey Schaufler <casey(a)schaufler-ca.com&gt; --- security/security.c | 29 +++++++++++++++++++++++++++++ 1 file changed, 29 insertions(+) diff --git a/security/security.c b/security/security.c index ddbaf2073b02..95b48721fb17 100644 --- a/security/security.c +++ b/security/security.c @@ -788,9 +788,38 @@ 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_display = lsm_task_display(from); + int to_display = lsm_task_display(to); + + /* + * If the display 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_display == LSMBLOB_INVALID) + from_display = 0; + if (to_display == LSMBLOB_INVALID) + to_display = 0; + if (from_display != to_display) + return -EINVAL; + return call_int_hook(binder_transaction, 0, from, to); }