linux-kernel - Re: autofs crash with latest linux-next

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Date:   Thu, 15 Oct 2020 12:28:14 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Krzysztof Kozlowski <krzk@...nel.org>
Cc:     Christian Borntraeger <borntraeger@...ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Christoph Hellwig <hch@...radead.org>,
        linux-kernel@...r.kernel.org,
        Linux-Next Mailing List <linux-next@...r.kernel.org>,
        "viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>
Subject: Re: autofs crash with latest linux-next

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/

-- 
Kees Cook