Commit 378ff1a5 authored by Al Viro's avatar Al Viro
Browse files

fix deadlock in cifs_ioctl_clone() 



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().

Cc: stable@vger.kernel.org @ 3.13+
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent ec6f34e5

fs/cifs/ioctl.c

+5 −16
Original line number Diff line number Diff line
@@ -86,21 +86,16 @@ static long cifs_ioctl_clone(unsigned int xid, struct file *dst_file, 
	}



	src_inode = file_inode(src_file.file);

	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:

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