From nobody Wed Apr 8 10:01:27 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id F341DC32792 for ; Sat, 20 Aug 2022 11:41:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345552AbiHTLlu (ORCPT ); Sat, 20 Aug 2022 07:41:50 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59018 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241192AbiHTLls (ORCPT ); Sat, 20 Aug 2022 07:41:48 -0400 Received: from sender-of-o50.zoho.in (sender-of-o50.zoho.in [103.117.158.50]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DC8909BB77; Sat, 20 Aug 2022 04:41:46 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1660995689; cv=none; d=zohomail.in; s=zohoarc; b=bzuIDQA+sR7ZiWE9DXMgKg0fHNUajlNkGygoTkXW2MW91KjrK5GL9eOKirNwxsPs/bJnNxQhnrknPFPij2k245WT0qW3D9ehEf52EbnOgIYV5FcRmt0UP5siCMl70q70faYcZAIhWPVIxmBHPr5TFhT/a2VU0hP4X9HwO8DZyjU= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zohomail.in; s=zohoarc; t=1660995689; h=Content-Type:Content-Transfer-Encoding:Cc:Date:From:MIME-Version:Message-ID:Subject:To; bh=OwlirewM9MHK3jNUDVvfjUe6e2E0DI0dbUmH8k2UzYQ=; b=GenioD5MecWkzSLRl/rhBypTtzqh1kkoLFw6k0FFqzkxpS8oGBx2LQASZNBlwQiz/k/4V4pgo3lArz+X2njw4pConEvuJE/v7KG8BpzgJNyeYx7OKReBvZjRVN85YedcxivMXxYTRPt4qmBYAqWdgMypT1LoMkK5opXE1HDkF0s= ARC-Authentication-Results: i=1; mx.zohomail.in; dkim=pass header.i=siddh.me; spf=pass smtp.mailfrom=code@siddh.me; dmarc=pass header.from= DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; t=1660995689; s=zmail; d=siddh.me; i=code@siddh.me; h=From:From:To:To:Cc:Cc:Message-ID:Subject:Subject:Date:Date:MIME-Version:Content-Transfer-Encoding:Content-Type:Message-Id:Reply-To; bh=OwlirewM9MHK3jNUDVvfjUe6e2E0DI0dbUmH8k2UzYQ=; b=fbzEaX1s4LxtB1mccW6+EkXK8lpWzjKTQ6YE28zZS4Z1v0I+Fjkwh9aFFNlfRXMo oLl/vzp3vCh/x/gPreCbabPT6O+WmH2NSifKmHL3//s7PlDfHdeTVUoHkhGW4duTx4w 3wcFsrXaZborYmXeobgoRkGXwvLhjr5Xo4i6GcaE= Received: from localhost.localdomain (43.250.157.244 [43.250.157.244]) by mx.zoho.in with SMTPS id 1660995687489847.0225686061804; Sat, 20 Aug 2022 17:11:27 +0530 (IST) From: Siddh Raman Pant To: Jens Axboe , Carlos Llamas Cc: linux-block , linux-kernel , linux-kernel-mentees , syzbot+a8e049cd3abd342936b6@syzkaller.appspotmail.com, stable@vger.kernel.org Message-ID: <20220820114105.8792-1-code@siddh.me> Subject: [PATCH] loop: Correct UAPI definitions to match with driver Date: Sat, 20 Aug 2022 17:11:05 +0530 X-Mailer: git-send-email 2.35.1 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-ZohoMailClient: External Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Syzkaller has reported a warning in iomap_iter(), which got triggered due to a call to iomap_iter_done() which has: WARN_ON_ONCE(iter->iomap.offset > iter->pos); The warning was triggered because `pos` was being negative. I was having offset =3D 0, pos =3D -2950420705881096192. This ridiculously negative value smells of an overflow, and sure it is. The userspace can configure a loop using an ioctl call, wherein a configuration of type loop_config is passed (see lo_ioctl()'s case on line 1550 of drivers/block/loop.c). This proceeds to call loop_configure() which in turn calls loop_set_status_from_info() (see line 1050 of loop.c), passing &config->info which is of type loop_info64*. This function then sets the appropriate values, like the offset. The problem here is loop_device has lo_offset of type loff_t (see line 52 of loop.c), which is typdef-chained to long long, whereas loop_info64 has lo_offset of type __u64 (see line 56 of include/uapi/linux/loop.h). The function directly copies offset from info to the device as follows (See line 980 of loop.c): lo->lo_offset =3D info->lo_offset; This results in the encountered overflow (in my case, the RHS was 15496323367828455424). Thus, convert the type definitions in loop_info64 to their signed counterparts in order to match definitions in loop_device, and check for negative value during loop_set_status_from_info(). Bug report: https://syzkaller.appspot.com/bug?id=3Dc620fe14aac810396d3c3edc= 9ad73848bf69a29e Reported-and-tested-by: syzbot+a8e049cd3abd342936b6@syzkaller.appspotmail.c= om Cc: stable@vger.kernel.org Signed-off-by: Siddh Raman Pant --- Unless I am missing any other uses or quirks of UAPI loop_info64, I think this won't introduce regression, since if something is working, it will continue to work. If something does break, then it was relying on overflows, which is anyways an incorrect way to go about. Also, it seems even the 32-bit compatibility structure uses the signed types (compat_loop_info uses compat_int_t which is s32), so this patch should be fine. drivers/block/loop.c | 3 +++ include/uapi/linux/loop.h | 12 ++++++------ 2 files changed, 9 insertions(+), 6 deletions(-) diff --git a/drivers/block/loop.c b/drivers/block/loop.c index e3c0ba93c1a3..4ca20ce3158d 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -977,6 +977,9 @@ loop_set_status_from_info(struct loop_device *lo, return -EINVAL; } =20 + if (info->lo_offset < 0 || info->lo_sizelimit < 0) + return -EINVAL; + lo->lo_offset =3D info->lo_offset; lo->lo_sizelimit =3D info->lo_sizelimit; memcpy(lo->lo_file_name, info->lo_file_name, LO_NAME_SIZE); diff --git a/include/uapi/linux/loop.h b/include/uapi/linux/loop.h index 6f63527dd2ed..973565f38f9d 100644 --- a/include/uapi/linux/loop.h +++ b/include/uapi/linux/loop.h @@ -53,12 +53,12 @@ struct loop_info64 { __u64 lo_device; /* ioctl r/o */ __u64 lo_inode; /* ioctl r/o */ __u64 lo_rdevice; /* ioctl r/o */ - __u64 lo_offset; - __u64 lo_sizelimit;/* bytes, 0 =3D=3D max available */ - __u32 lo_number; /* ioctl r/o */ - __u32 lo_encrypt_type; /* obsolete, ignored */ - __u32 lo_encrypt_key_size; /* ioctl w/o */ - __u32 lo_flags; + __s64 lo_offset; + __s64 lo_sizelimit;/* bytes, 0 =3D=3D max available */ + __s32 lo_number; /* ioctl r/o */ + __s32 lo_encrypt_type; /* obsolete, ignored */ + __s32 lo_encrypt_key_size; /* ioctl w/o */ + __s32 lo_flags; __u8 lo_file_name[LO_NAME_SIZE]; __u8 lo_crypt_name[LO_NAME_SIZE]; __u8 lo_encrypt_key[LO_KEY_SIZE]; /* ioctl w/o */ --=20 2.35.1