UPSTREAM: binder: fix proc->files use-after-free
proc->files cleanup is initiated by binder_vma_close. Therefore
a reference on the binder_proc is not enough to prevent the
files_struct from being released while the binder_proc still has
a reference. This can lead to an attempt to dereference the
stale pointer obtained from proc->files prior to proc->files
cleanup. This has been seen once in task_get_unused_fd_flags()
when __alloc_fd() is called with a stale "files".
The fix is to protect proc->files with a mutex to prevent cleanup
while in use.
Signed-off-by: Todd Kjos <tkjos@google.com>
Cc: stable <stable@vger.kernel.org> # 4.14
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 7f3dc0088b98533f17128058fac73cd8b2752ef1)
Change-Id: I40982bb0b4615bda5459538c20eb2a913964042c
diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index b04051f..1da0d31 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -506,7 +506,8 @@
* @tsk task_struct for group_leader of process
* (invariant after initialized)
* @files files_struct for process
- * (invariant after initialized)
+ * (protected by @files_lock)
+ * @files_lock mutex to protect @files
* @deferred_work_node: element for binder_deferred_list
* (protected by binder_deferred_lock)
* @deferred_work: bitmap of deferred work to perform
@@ -554,6 +555,7 @@
int pid;
struct task_struct *tsk;
struct files_struct *files;
+ struct mutex files_lock;
struct hlist_node deferred_work_node;
int deferred_work;
bool is_dead;
@@ -904,20 +906,26 @@
static int task_get_unused_fd_flags(struct binder_proc *proc, int flags)
{
- struct files_struct *files = proc->files;
unsigned long rlim_cur;
unsigned long irqs;
+ int ret;
- if (files == NULL)
- return -ESRCH;
-
- if (!lock_task_sighand(proc->tsk, &irqs))
- return -EMFILE;
-
+ mutex_lock(&proc->files_lock);
+ if (proc->files == NULL) {
+ ret = -ESRCH;
+ goto err;
+ }
+ if (!lock_task_sighand(proc->tsk, &irqs)) {
+ ret = -EMFILE;
+ goto err;
+ }
rlim_cur = task_rlimit(proc->tsk, RLIMIT_NOFILE);
unlock_task_sighand(proc->tsk, &irqs);
- return __alloc_fd(files, 0, rlim_cur, flags);
+ ret = __alloc_fd(proc->files, 0, rlim_cur, flags);
+err:
+ mutex_unlock(&proc->files_lock);
+ return ret;
}
/*
@@ -926,8 +934,10 @@
static void task_fd_install(
struct binder_proc *proc, unsigned int fd, struct file *file)
{
+ mutex_lock(&proc->files_lock);
if (proc->files)
__fd_install(proc->files, fd, file);
+ mutex_unlock(&proc->files_lock);
}
/*
@@ -937,9 +947,11 @@
{
int retval;
- if (proc->files == NULL)
- return -ESRCH;
-
+ mutex_lock(&proc->files_lock);
+ if (proc->files == NULL) {
+ retval = -ESRCH;
+ goto err;
+ }
retval = __close_fd(proc->files, fd);
/* can't restart close syscall because file table entry was cleared */
if (unlikely(retval == -ERESTARTSYS ||
@@ -947,7 +959,8 @@
retval == -ERESTARTNOHAND ||
retval == -ERESTART_RESTARTBLOCK))
retval = -EINTR;
-
+err:
+ mutex_unlock(&proc->files_lock);
return retval;
}
@@ -4737,7 +4750,9 @@
ret = binder_alloc_mmap_handler(&proc->alloc, vma);
if (ret)
return ret;
+ mutex_lock(&proc->files_lock);
proc->files = get_files_struct(current);
+ mutex_unlock(&proc->files_lock);
return 0;
err_bad_arg:
@@ -4761,6 +4776,7 @@
spin_lock_init(&proc->outer_lock);
get_task_struct(current->group_leader);
proc->tsk = current->group_leader;
+ mutex_init(&proc->files_lock);
INIT_LIST_HEAD(&proc->todo);
if (binder_supported_policy(current->policy)) {
proc->default_priority.sched_policy = current->policy;
@@ -5020,9 +5036,11 @@
files = NULL;
if (defer & BINDER_DEFERRED_PUT_FILES) {
+ mutex_lock(&proc->files_lock);
files = proc->files;
if (files)
proc->files = NULL;
+ mutex_unlock(&proc->files_lock);
}
if (defer & BINDER_DEFERRED_FLUSH)
