Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <000000000000dbce4e05f170f289@google.com> <5f45bb9a-5e00-48dd-82b0-46b19b1b98a3@app.fastmail.com>
 <CAHk-=wi8XyAUF9_z6-oa4Ava6PVZeE-=TVNcFK1puQHpOtqLLw@mail.gmail.com>
 <ab7a9477-ddc7-430f-b4ee-c67251e879b0@app.fastmail.com> <1bd49fc0-d64f-4eb8-841a-4b09e178b5fd@gmail.com>
In-Reply-To: <1bd49fc0-d64f-4eb8-841a-4b09e178b5fd@gmail.com>
From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Thu, 5 Jan 2023 13:53:59 -0800
Message-ID: <CAHk-=wg3U3Y6eaura=xQzTsktpEOMETYYnue+_KSbQmpg7vZ0Q@mail.gmail.com>
Subject: Re: [syzbot] [hfs?] WARNING in hfs_write_inode
To:     Michael Schmitz <schmitzmic@gmail.com>
Cc:     Arnd Bergmann <arnd@arndb.de>,
        syzbot <syzbot+7bb7cd3595533513a9e7@syzkaller.appspotmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        christian.brauner@ubuntu.com,
        Damien Le Moal <damien.lemoal@opensource.wdc.com>,
        jlayton@kernel.org, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com,
        Matthew Wilcox <willy@infradead.org>,
        ZhangPeng <zhangpeng362@huawei.com>,
        Viacheslav Dubeyko <slava@dubeyko.com>,
        linux-m68k@lists.linux-m68k.org, flar@allandria.com
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Thu, Jan 5, 2023 at 1:35 PM Michael Schmitz <schmitzmic@gmail.com> wrote:
>
> Looking at Linus' patch, I wonder whether the missing fd.entrylength
> size test in the HFS_IS_RSRC(inode) case was due to the fact that a
> file's resource fork may be empty?

But if that is the case, then the subsequent hfs_bnode_read would
return garbage, no? And then writing it back after the update would be
even worse.

So adding that

+               if (fd.entrylength < sizeof(struct hfs_cat_file))
+                       goto out;

would seem to be the right thing anyway. No?

But I really don't know the code, so this is all from just looking at
it and going "that makes no sense". Maybe it _does_ make sense to
people who have more background on it.

             Linus