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From:   Sven Schnelle <svens@linux.ibm.com>
To:     Kees Cook <keescook@chromium.org>
Cc:     Krzysztof Kozlowski <krzk@kernel.org>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Christoph Hellwig <hch@infradead.org>,
        linux-kernel@vger.kernel.org,
        Linux-Next Mailing List <linux-next@vger.kernel.org>,
        "viro@zeniv.linux.org.uk" <viro@zeniv.linux.org.uk>
Subject: Re: autofs crash with latest linux-next
References: <yt9d1ri3nakg.fsf@linux.ibm.com>
        <8a4c7324-4637-7f25-82b6-2fd30aacb73e@de.ibm.com>
        <20201014071547.GA2459@kozik-lap> <202010151226.7382E03@keescook>
Date:   Fri, 16 Oct 2020 07:44:14 +0200
In-Reply-To: <202010151226.7382E03@keescook> (Kees Cook's message of "Thu, 15
        Oct 2020 12:28:14 -0700")
Message-ID: <yt9dblh2sp1t.fsf@linux.ibm.com>
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Kees Cook <keescook@chromium.org> writes:

> On Wed, Oct 14, 2020 at 09:15:47AM +0200, Krzysztof Kozlowski wrote:
>> I hit this since few days as well. Although the bisect points to the
>> merge, the issue looks like a result of mentioned commit 4d03e3cc5982
>> ("fs: don't allow kernel reads and writes without iter ops").
>> 
>> The __kernel_read() last argument 'pos' can be NULL and it is
>> dereferenced here (added by the commit):
>> 
>>  525 ssize_t __kernel_write(struct file *file, const void *buf, size_t count, loff_t *pos)
>> ...
>>  547         kiocb.ki_pos = *pos;
>>  548         iov_iter_kvec(&iter, WRITE, &iov, 1, iov.iov_len);
>> 
>> 
>> The __kernel_read() is called with NULL in fs/autofs/waitq.c:
>> 
>>  45 static int autofs_write(struct autofs_sb_info *sbi,
>>  46                         struct file *file, const void *addr, int bytes)
>> 
>> ...
>>  54         mutex_lock(&sbi->pipe_mutex);
>>  55         while (bytes) {
>>  56                 wr = __kernel_write(file, data, bytes, NULL);
>
> I think the thread here is the same thing, but you've found it in
> autofs...
> https://lore.kernel.org/lkml/CAHk-=wgj=mKeN-EfV5tKwJNeHPLG0dybq+R5ZyGuc4WeUnqcmA@mail.gmail.com/

Indeed. Thanks, missed that.

Sven