ksmbd: zero the FS_OBJECT_ID_INFORMATION buffer before filling it in

smb2_get_info_filesystem() reports 64 bytes for FS_OBJECT_ID_INFORMATION,
that is the whole of struct object_id_info, but writes only 46 of them:

 - objid[] is 16 bytes, and when the volume UUID is not available only
   sizeof(stfs.f_fsid) (8) bytes are copied into it;
 - extended_info.version_string[] is STRING_LENGTH (28) bytes, and only
   strlen("1.1.0") (5) bytes are copied into it.

The response buffer is zeroed on allocation (kvzalloc() in
smb2_allocate_rsp_buf()), so for a standalone request the remaining 31
bytes are zero.  In a compound request they need not be.  The offset of
the next response is advanced by the length pinned for the previous one,
so if a preceding command wrote its reply into the buffer and then
failed, smb2_set_err_rsp() pins only the short error response and the
next reply lands inside the area that has already been written.  Only
the header is cleared there:

	memset((char *)rsp_hdr, 0, sizeof(struct smb2_hdr) + 2);

The client then receives up to 31 bytes of a response it was not meant
to see, including one that failed with an access denied error.

Clear the structure before filling it in.  As a side effect
version_string is now NUL terminated.

Fixes: e2f34481b2 ("cifsd: add server-side procedures for SMB3")
Suggested-by: ChenXiaoSong <chenxiaosong@chenxiaosong.com>
Cc: stable@vger.kernel.org
Signed-off-by: Aleksandr Khromov <haa@amicon.ru>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>

fs/smb/server/smb2pdu.c

@@ -7444,6 +7444,7 @@ static int smb2_get_info_filesystem(struct ksmbd_work *work,
 		struct object_id_info *info;
 
 		info = (struct object_id_info *)(rsp->Buffer);
+		memset(info, 0, sizeof(*info));
 
 		if (path.mnt->mnt_sb->s_uuid_len == 16)
 			memcpy(info->objid, path.mnt->mnt_sb->s_uuid.b,