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 | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
--- a/drivers/android/binder.c +++ b/drivers/android/binder.c @@ -303,6 +303,7 @@ struct binder_proc { struct task_struct *tsk; struct files_struct *files; struct mutex files_lock; + const struct cred *cred; struct hlist_node deferred_work_node; int deferred_work; void *buffer; @@ -1505,7 +1506,7 @@ 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; @@ -3036,6 +3037,7 @@ static int binder_open(struct inode *nod get_task_struct(current->group_leader); proc->tsk = current->group_leader; mutex_init(&proc->files_lock); + proc->cred = get_cred(filp->f_cred); INIT_LIST_HEAD(&proc->todo); init_waitqueue_head(&proc->wait); proc->default_priority = task_nice(current); @@ -3241,6 +3243,7 @@ static void binder_deferred_release(stru }
put_task_struct(proc->tsk); + put_cred(proc->cred);
binder_debug(BINDER_DEBUG_OPEN_CLOSE, "%s: %d threads %d, nodes %d (ref %d), refs %d, active transactions %d, buffers %d, pages %d\n",