Staging: android: task_get_unused_fd_flags: fix the wrong usage of tsk->signal

Compile tested.

task_struct->signal is not protected by RCU, the code is bogus.
Change the code to take ->siglock to pin ->signal.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Arve Hjønnevåg <arve@android.com>
Cc: Brian Swetland <swetland@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 5 insertions, 5 deletions

diff --git a/drivers/staging/android/binder.c b/drivers/staging/android/binder.c
index ab014bc9683..758131cad08 100644
--- a/drivers/staging/android/binder.c
+++ b/drivers/staging/android/binder.c
@@ -319,6 +319,7 @@ int task_get_unused_fd_flags(struct task_struct *tsk, int flags)
         int fd, error;
         struct fdtable *fdt;
         unsigned long rlim_cur;
+        unsigned long irqs;
 
         if (files == NULL)
                 return -ESRCH;
@@ -335,12 +336,11 @@ repeat:
          * N.B. For clone tasks sharing a files structure, this test
          * will limit the total number of files that can be opened.
          */
-        rcu_read_lock();
-        if (tsk->signal)
+        rlim_cur = 0;
+        if (lock_task_sighand(tsk, &irqs)) {
                 rlim_cur = tsk->signal->rlim[RLIMIT_NOFILE].rlim_cur;
-        else
-                rlim_cur = 0;
-        rcu_read_unlock();
+                unlock_task_sighand(tsk, &irqs);
+        }
         if (fd >= rlim_cur)
                 goto out;