[CIFS] Byte range unlock request to non-Unix server can unlock too much

On a mount without posix extensions enabled, when an unlock request is
made, the client can release more than is intended. To reproduce, on a
CIFS mount without posix extensions enabled:

1) open file
2) do fcntl lock: start=0 len=1
3) do fcntl lock: start=2 len=1
4) do fcntl unlock: start=0 len=1

...on the unlock call the client sends an unlock request to the server
for both locks. The problem is a bad test in cifs_lock.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index 894b1f7b299d..f9bd8b83f40e 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -767,7 +767,8 @@ int cifs_lock(struct file *file, int cmd, struct file_lock *pfLock)
                         mutex_lock(&fid->lock_mutex);
                         list_for_each_entry_safe(li, tmp, &fid->llist, llist) {
                                 if (pfLock->fl_start <= li->offset &&
-                                                length >= li->length) {
+                                                (pflock->fl_start + length) >=
+                                                (li->offset + li->length)) {
                                         stored_rc = CIFSSMBLock(xid, pTcon,
                                                         netfid,
                                                         li->length, li->offset,