ksmbd: add permission checks for FSCTL_DUPLICATE_EXTENTS_TO_FILE

commit 388e413 upstream.

The FSCTL_DUPLICATE_EXTENTS_TO_FILE arm of smb2_ioctl() overwrites the
destination file's data via vfs_clone_file_range() with neither the
share-level KSMBD_TREE_CONN_FLAG_WRITABLE check nor a per-handle
fp->daccess check that the other write-bearing arms carry. A client can
overwrite destination data on a read-only share, or from a handle opened
with only FILE_WRITE_ATTRIBUTES (which still yields an FMODE_WRITE filp).
FILE_WRITE_ATTRIBUTES-only destination handle overwrote the file's data via
the clone. Add both checks, matching the FSCTL_SET_SPARSE permission fix;
require FILE_WRITE_DATA since this writes data.

Cc: stable@vger.kernel.org
Signed-off-by: Gil Portnoy <dddhkts1@gmail.com>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: dhkts1

fs/smb/server/smb2pdu.c

@@ -8482,6 +8482,17 @@ int smb2_ioctl(struct ksmbd_work *work)
 			goto dup_ext_out;
 		}
 
+		if (!test_tree_conn_flag(work->tcon,
+					 KSMBD_TREE_CONN_FLAG_WRITABLE)) {
+			ret = -EACCES;
+			goto dup_ext_out;
+		}
+
+		if (!(fp_out->daccess & FILE_WRITE_DATA_LE)) {
+			ret = -EACCES;
+			goto dup_ext_out;
+		}
+
 		src_off = le64_to_cpu(dup_ext->SourceFileOffset);
 		dst_off = le64_to_cpu(dup_ext->TargetFileOffset);
 		length = le64_to_cpu(dup_ext->ByteCount);