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fix deadlock in cifs_ioctl_clone()

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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: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2015-01-18 23:37:32 -05:00
parent ec6f34e5b5
commit 378ff1a53b
1 changed files with 5 additions and 16 deletions
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21
fs/cifs/ioctl.c
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@ -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: