blob: 5ec5e218a0b676cd8dff81d53907269d39ac0f09 [file] [log] [blame]
From 750850d7a8ef65d7b088c6b8e8700d36b37bf6ab Mon Sep 17 00:00:00 2001
From: Christian Brauner <>
Date: Wed, 11 Mar 2020 11:53:09 +0100
Subject: [PATCH] binderfs: use refcount for binder control devices too
commit 211b64e4b5b6bd5fdc19cd525c2cc9a90e6b0ec9 upstream.
Binderfs binder-control devices are cleaned up via binderfs_evict_inode
too() which will use refcount_dec_and_test(). However, we missed to set
the refcount for binderfs binder-control devices and so we underflowed
when the binderfs instance got unmounted. Pretty obvious oversight and
should have been part of the more general UAF fix. The good news is that
having test cases (suprisingly) helps.
Technically, we could detect that we're about to cleanup the
binder-control dentry in binderfs_evict_inode() and then simply clean it
up. But that makes the assumption that the binder driver itself will
never make use of a binderfs binder-control device after the binderfs
instance it belongs to has been unmounted and the superblock for it been
destroyed. While it is unlikely to ever come to this let's be on the
safe side. Performance-wise this also really doesn't matter since the
binder-control device is only every really when creating the binderfs
filesystem or creating additional binder devices. Both operations are
pretty rare.
Fixes: f0fe2c0f050d ("binder: prevent UAF for binderfs devices II")
Reported-by: Naresh Kamboju <>
Signed-off-by: Christian Brauner <>
Acked-by: Todd Kjos <>
Signed-off-by: Greg Kroah-Hartman <>
Signed-off-by: Paul Gortmaker <>
diff --git a/drivers/android/binderfs.c b/drivers/android/binderfs.c
index 86b8dc3acbd6..67982cabe068 100644
--- a/drivers/android/binderfs.c
+++ b/drivers/android/binderfs.c
@@ -439,6 +439,7 @@ static int binderfs_binder_ctl_create(struct super_block *sb)
inode->i_uid = info->root_uid;
inode->i_gid = info->root_gid;
+ refcount_set(&device->ref, 1);
device->binderfs_inode = inode;
device->miscdev.minor = minor;