android_kernel_samsung_msm8976/fs/configfs
Junxiao Bi 7a4ca2033f configfs: fix race between dentry put and lookup
commit 76ae281f6307331aa063288edb6422ae99f435f0 upstream.

A race window in configfs, it starts from one dentry is UNHASHED and end
before configfs_d_iput is called.  In this window, if a lookup happen,
since the original dentry was UNHASHED, so a new dentry will be
allocated, and then in configfs_attach_attr(), sd->s_dentry will be
updated to the new dentry.  Then in configfs_d_iput(),
BUG_ON(sd->s_dentry != dentry) will be triggered and system panic.

sys_open:                     sys_close:
 ...                           fput
                                dput
                                 dentry_kill
                                  __d_drop <--- dentry unhashed here,
                                           but sd->dentry still point
                                           to this dentry.

 lookup_real
  configfs_lookup
   configfs_attach_attr---> update sd->s_dentry
                            to new allocated dentry here.

                                   d_kill
                                     configfs_d_iput <--- BUG_ON(sd->s_dentry != dentry)
                                                     triggered here.

To fix it, change configfs_d_iput to not update sd->s_dentry if
sd->s_count > 2, that means there are another dentry is using the sd
beside the one that is going to be put.  Use configfs_dirent_lock in
configfs_attach_attr to sync with configfs_d_iput.

With the following steps, you can reproduce the bug.

1. enable ocfs2, this will mount configfs at /sys/kernel/config and
   fill configure in it.

2. run the following script.
	while [ 1 ]; do cat /sys/kernel/config/cluster/$your_cluster_name/idle_timeout_ms > /dev/null; done &
	while [ 1 ]; do cat /sys/kernel/config/cluster/$your_cluster_name/idle_timeout_ms > /dev/null; done &

Signed-off-by: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2013-11-29 11:11:53 -08:00
..
configfs_internal.h make configfs_pin_fs() return root dentry on success 2012-03-20 21:29:48 -04:00
dir.c configfs: fix race between dentry put and lookup 2013-11-29 11:11:53 -08:00
file.c
inode.c userns: Convert configfs to use kuid and kgid where appropriate 2012-09-18 01:01:37 -07:00
item.c doc: fix broken references 2011-09-27 18:08:04 +02:00
Kconfig configfs: change depends -> select SYSFS 2011-01-16 21:22:29 +00:00
Makefile
mount.c fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
symlink.c configfs: kill configfs_sb 2012-03-20 21:29:47 -04:00