android: drivers: Avoid debugfs race in binder

If a /d/binder/proc/[pid] entry is kept open after linux has
torn down the associated process, binder_proc_show can deference
an invalid binder_proc that has been stashed in the debugfs
inode.  Validate that the binder_proc ptr passed into binder_proc_show
has not been freed by looking for it within the global process list
whilst the global lock is held. If the ptr is not valid, print nothing.

Cc: Colin Cross <ccross@android.com>
Cc: Arve Hjønnevåg <arve@android.com>
Cc: Dmitry Shmidt <dimitrysh@google.com>
Cc: Rom Lemarchand <romlem@google.com>
Cc: Serban Constantinescu <serban.constantinescu@arm.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Android Kernel Team <kernel-team@android.com>
Signed-off-by: Dmitry Shmidt <dimitrysh@google.com>
[jstultz: Minor commit message tweaks]
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index 1db3761..f0ce995 100644 (file)
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -3600,13 +3600,24 @@ static int binder_transactions_show(struct seq_file *m, void *unused)
 
 static int binder_proc_show(struct seq_file *m, void *unused)
 {
+       struct binder_proc *itr;
        struct binder_proc *proc = m->private;
        int do_lock = !binder_debug_no_lock;
+       bool valid_proc = false;
 
        if (do_lock)
                binder_lock(__func__);
-       seq_puts(m, "binder proc state:\n");
-       print_binder_proc(m, proc, 1);
+
+       hlist_for_each_entry(itr, &binder_procs, proc_node) {
+               if (itr == proc) {
+                       valid_proc = true;
+                       break;
+               }
+       }
+       if (valid_proc) {
+               seq_puts(m, "binder proc state:\n");
+               print_binder_proc(m, proc, 1);
+       }
        if (do_lock)
                binder_unlock(__func__);
        return 0;