Commit 29bc22ac authored by Todd Kjos's avatar Todd Kjos Committed by Paul Moore
Browse files

binder: use euid from cred instead of using task 



Save the 'struct cred' associated with a binder process
at initial open to avoid potential race conditions
when converting to an euid.

Set a transaction's sender_euid from the 'struct cred'
saved at binder_open() instead of looking up the euid
from the binder proc's 'struct task'. This ensures
the euid is associated with the security context that
of the task that opened binder.

Cc: stable@vger.kernel.org # 4.4+
Fixes: 457b9a6f ("Staging: android: add binder driver")
Signed-off-by: default avatarTodd Kjos <tkjos@google.com>
Suggested-by: default avatarStephen Smalley <stephen.smalley.work@gmail.com>
Suggested-by: default avatarJann Horn <jannh@google.com>
Acked-by: default avatarCasey Schaufler <casey@schaufler-ca.com>
Signed-off-by: default avatarPaul Moore <paul@paul-moore.com>
parent 86dd9fd5

drivers/android/binder.c

+3 −1
Original line number Diff line number Diff line
@@ -2702,7 +2702,7 @@ static void binder_transaction(struct binder_proc *proc, 
		t->from = thread;

	else

		t->from = NULL;

	t->sender_euid = task_euid(proc->tsk);

	t->sender_euid = proc->cred->euid;

	t->to_proc = target_proc;

	t->to_thread = target_thread;

	t->code = tr->code;
@@ -4343,6 +4343,7 @@ static void binder_free_proc(struct binder_proc *proc) 
	}

	binder_alloc_deferred_release(&proc->alloc);

	put_task_struct(proc->tsk);

	put_cred(proc->cred);

	binder_stats_deleted(BINDER_STAT_PROC);

	kfree(proc);

}
@@ -5021,6 +5022,7 @@ static int binder_open(struct inode *nodp, struct file *filp) 
	spin_lock_init(&proc->outer_lock);

	get_task_struct(current->group_leader);

	proc->tsk = current->group_leader;

	proc->cred = get_cred(filp->f_cred);

	INIT_LIST_HEAD(&proc->todo);

	init_waitqueue_head(&proc->freeze_wait);

	proc->default_priority = task_nice(current);

drivers/android/binder_internal.h

+4 −0
Original line number Diff line number Diff line
@@ -364,6 +364,9 @@ struct binder_ref { 
 *                        (invariant after initialized)

 * @tsk                   task_struct for group_leader of process

 *                        (invariant after initialized)

 * @cred                  struct cred associated with the `struct file`

 *                        in binder_open()

 *                        (invariant after initialized)

 * @deferred_work_node:   element for binder_deferred_list

 *                        (protected by binder_deferred_lock)

 * @deferred_work:        bitmap of deferred work to perform
@@ -424,6 +427,7 @@ struct binder_proc { 
	struct list_head waiting_threads;

	int pid;

	struct task_struct *tsk;

	const struct cred *cred;

	struct hlist_node deferred_work_node;

	int deferred_work;

	int outstanding_txns;