From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id F0743C433E6 for ; Tue, 23 Feb 2021 17:03:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B780264E7C for ; Tue, 23 Feb 2021 17:03:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233731AbhBWRCs (ORCPT ); Tue, 23 Feb 2021 12:02:48 -0500 Received: from mx2.suse.de ([195.135.220.15]:56686 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233690AbhBWRCA (ORCPT ); Tue, 23 Feb 2021 12:02:00 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id B63E3ACBF; Tue, 23 Feb 2021 17:01:18 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 651021E14EF; Tue, 23 Feb 2021 18:01:18 +0100 (CET) Date: Tue, 23 Feb 2021 18:01:18 +0100 From: Jan Kara To: Sabyrzhan Tasbolatov Cc: tytso@mit.edu, adilger.kernel@dilger.ca, linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, syzbot+a8b4b0c60155e87e9484@syzkaller.appspotmail.com Subject: Re: [PATCH] fs/ext4: fix integer overflow in s_log_groups_per_flex Message-ID: <20210223170118.GD30433@quack2.suse.cz> References: <20210203134351.1697508-1-snovitoll@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210203134351.1697508-1-snovitoll@gmail.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 03-02-21 19:43:51, Sabyrzhan Tasbolatov wrote: > syzbot found UBSAN: shift-out-of-bounds in ext4_mb_init [1], when > 1 << sbi->s_es->s_log_groups_per_flex is bigger than UINT_MAX, > where sbi->s_mb_prefetch is unsigned integer type. > > 32 is the maximum allowed power of s_log_groups_per_flex. Following if > check will also trigger UBSAN shift-out-of-bound: > > if (1 << sbi->s_es->s_log_groups_per_flex > UINT_MAX) { > > So I'm checking it against the raw number, perhaps there is another way > to calculate UINT_MAX max power. Also use min_t as to make sure it's > uint type. > > [1] UBSAN: shift-out-of-bounds in fs/ext4/mballoc.c:2713:24 > shift exponent 60 is too large for 32-bit type 'int' > Call Trace: > __dump_stack lib/dump_stack.c:79 [inline] > dump_stack+0x137/0x1be lib/dump_stack.c:120 > ubsan_epilogue lib/ubsan.c:148 [inline] > __ubsan_handle_shift_out_of_bounds+0x432/0x4d0 lib/ubsan.c:395 > ext4_mb_init_backend fs/ext4/mballoc.c:2713 [inline] > ext4_mb_init+0x19bc/0x19f0 fs/ext4/mballoc.c:2898 > ext4_fill_super+0xc2ec/0xfbe0 fs/ext4/super.c:4983 > > Reported-by: syzbot+a8b4b0c60155e87e9484@syzkaller.appspotmail.com > Signed-off-by: Sabyrzhan Tasbolatov > --- > fs/ext4/mballoc.c | 11 +++++++++-- > 1 file changed, 9 insertions(+), 2 deletions(-) > > diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c > index 99bf091fee10..e1e7ffbba1a6 100644 > --- a/fs/ext4/mballoc.c > +++ b/fs/ext4/mballoc.c > @@ -2709,8 +2709,15 @@ static int ext4_mb_init_backend(struct super_block *sb) > } > > if (ext4_has_feature_flex_bg(sb)) { > - /* a single flex group is supposed to be read by a single IO */ > - sbi->s_mb_prefetch = min(1 << sbi->s_es->s_log_groups_per_flex, > + /* a single flex group is supposed to be read by a single IO. > + * 2 ^ s_log_groups_per_flex != UINT_MAX as s_mb_prefetch is > + * unsigned integer, so the maximum shift is 32. > + */ > + if (sbi->s_es->s_log_groups_per_flex > 32) { ^^ >= 32? Otherwise the patch looks good. Honza > + ext4_msg(sb, KERN_ERR, "too many log groups per flexible block group"); > + goto err_freesgi; > + } > + sbi->s_mb_prefetch = min_t(uint, 1 << sbi->s_es->s_log_groups_per_flex, > BLK_MAX_SEGMENT_SIZE >> (sb->s_blocksize_bits - 9)); > sbi->s_mb_prefetch *= 8; /* 8 prefetch IOs in flight at most */ > } else { > -- > 2.25.1 > -- Jan Kara SUSE Labs, CR