[PATCH 3.13.y-ckt 087/103] fix deadlock in cifs_ioctl_clone()

Kamal Mostafa
2015-02-19T00:41:11Z

From: Al Viro <viro@zeniv.linux.org.uk>

commit 378ff1a53b5724f3ac97b0aba3c9ecac072f6fcd upstream.

It really needs to check that src is non-directory *and* use
{un,}lock_two_nodirectories(). As it is, it's trivial to cause
double-lock (ioctl(fd, CIFS_IOC_COPYCHUNK_FILE, fd)) and if the
last argument is an fd of directory, we are asking for trouble
by violating the locking order - all directories go before all
non-directories. If the last argument is an fd of parent
directory, it has 50% odds of locking child before parent,
which will cause AB-BA deadlock if we race with unlink().

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
fs/cifs/ioctl.c | 21 +++++----------------
1 file changed, 5 insertions(+), 16 deletions(-)

diff --git a/fs/cifs/ioctl.c b/fs/cifs/ioctl.c
index 7749230..dfc9564 100644
--- a/fs/cifs/ioctl.c
+++ b/fs/cifs/ioctl.c
@@ -86,21 +86,16 @@ static long cifs_ioctl_clone(unsigned int xid, struct file *dst_file,
}

src_inode = src_file.file->f_dentry->d_inode;
+ rc = -EINVAL;
+ if (S_ISDIR(src_inode->i_mode))
+ goto out_fput;

/*
* Note: cifs case is easier than btrfs since server responsible for
* checks for proper open modes and file type and if it wants
* server could even support copy of range where source = target
*/
-
- /* so we do not deadlock racing two ioctls on same files */
- if (target_inode < src_inode) {
- mutex_lock_nested(&target_inode->i_mutex, I_MUTEX_PARENT);
- mutex_lock_nested(&src_inode->i_mutex, I_MUTEX_CHILD);
- } else {
- mutex_lock_nested(&src_inode->i_mutex, I_MUTEX_PARENT);
- mutex_lock_nested(&target_inode->i_mutex, I_MUTEX_CHILD);
- }
+ lock_two_nondirectories(target_inode, src_inode);

/* determine range to clone */
rc = -EINVAL;
@@ -124,13 +119,7 @@ static long cifs_ioctl_clone(unsigned int xid, struct file *dst_file,
out_unlock:
/* although unlocking in the reverse order from locking is not
strictly necessary here it is a little cleaner to be consistent */
- if (target_inode < src_inode) {
- mutex_unlock(&src_inode->i_mutex);
- mutex_unlock(&target_inode->i_mutex);
- } else {
- mutex_unlock(&target_inode->i_mutex);
- mutex_unlock(&src_inode->i_mutex);
- }
+ unlock_two_nondirectories(src_inode, target_inode);
out_fput:
fdput(src_file);
out_drop_write:
--
1.9.1