From: Todd Kjos tkjos@google.com
commit 29bc22ac5e5bc63275e850f0c8fc549e3d0e306b upstream.
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: 457b9a6f09f0 ("Staging: android: add binder driver") Signed-off-by: Todd Kjos tkjos@google.com Suggested-by: Stephen Smalley stephen.smalley.work@gmail.com Suggested-by: Jann Horn jannh@google.com Acked-by: Casey Schaufler casey@schaufler-ca.com Signed-off-by: Paul Moore paul@paul-moore.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/android/binder.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)
--- a/drivers/android/binder.c +++ b/drivers/android/binder.c @@ -424,6 +424,9 @@ enum binder_deferred_state { * (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 @@ -469,6 +472,7 @@ 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; bool is_dead; @@ -3091,7 +3095,7 @@ static void binder_transaction(struct bi 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; @@ -4707,6 +4711,7 @@ static void binder_free_proc(struct bind } binder_alloc_deferred_release(&proc->alloc); put_task_struct(proc->tsk); + put_cred(proc->cred); binder_stats_deleted(BINDER_STAT_PROC); kfree(proc); } @@ -5234,6 +5239,7 @@ static int binder_open(struct inode *nod 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); proc->default_priority = task_nice(current); /* binderfs stashes devices in i_private */