linux-kernel - Re: [v2] ubifs: Fix read out-of-bounds in ubifs_jnl_write

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Date:   Thu, 4 Mar 2021 09:50:29 +0800
From:   Chengsong Ke <kechengsong@...wei.com>
To:     <richard@....at>
CC:     <linux-mtd@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
        <chengzhihao1@...wei.com>
Subject: Re: [v2] ubifs: Fix read out-of-bounds in ubifs_jnl_write_inode()

ping

>> Reproducer:
>> 0. config KASAN && apply print.patch
>> 1. mount ubifs on /root/temp
>> 2. run test.sh
> 
> What does test.sh do?
Go to Link: https://bugzilla.kernel.org/show_bug.cgi?id=210865.
test.sh creates a very long path file test_file, and then create a 
symbol link link_file for test_file, so ubifs inode for link_file will 
be assigned a big value for ui->data_len.
When we change atime for link_file, ubifs_jnl_write_inode will be 
executed by wb_writeback. By this way, write_len could be not aligned 
with 8 bytes.
> 
>> 3. cd /root/temp && ls // change atime for link_file
>> 4. wait 1~2 minutes
>>
>> In order to solve the read oob problem in ubifs_wbuf_write_nolock, just align
>> the write_len to
>> 8 bytes when alloc the memory. So that this patch will not affect the use of
>> write_len in other
>> functions, such as ubifs_jnl_write_inode->make_reservation and
>> ubifs_jnl_write_inode->ubifs_node_calc_hash.
> 
> I gave this a second thought and I'm not so sure anymore what exactly is going on.
> The problem is real, I fully agree with you but I need to dig deeper into
> the journal and wbuf code to double check that we really fix the right thing
> and not just paper other something.
> 
> Thanks,
> //richard
> .
>