linux-kernel - Re: [PATCH] ext2/super: Fix a possible sleep-in-atomic bug in parse

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Message-ID: <a38d3308-2d7c-4ee2-c2b6-759f411bfd45@163.com>
Date:   Sat, 7 Oct 2017 09:55:02 +0800
From:   Jia-Ju Bai <baijiaju1990@....com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Al Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.com>,
        Sagi Grimberg <sagi@...mberg.me>, james.smart@...adcom.com,
        "linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ext2/super: Fix a possible sleep-in-atomic bug in
 parse_options

Thanks for your reply.
I agree that extra allocation in match_number() and match_u64int() may 
be unnecessary.

Thanks,
Jia-Ju Bai


On 2017/10/7 9:37, Linus Torvalds wrote:
> On Fri, Oct 6, 2017 at 6:20 PM, Jia-Ju Bai <baijiaju1990@....com> wrote:
>> To fix it, GFP_KERNEL is replaced with GFP_ATOMIC.
>> This bug is found by my static analysis tool and my code review.
> I'm not saying your patch is wrong, but it's a shame that we do that
> extra allocation in match_number() and match_u64int(), and that we
> don't have anything that is just size-limited.
>
> And there really isn't anything saying that we shouldn't do the same
> silly thing to match_u64int(). Maybe we don't have any actual users
> that need it for now, but still..
>
> Oh well.
>
> I do wonder if we shouldn't just use something like
>
>   "skip leading zeroes, copy to size-limited stack location instead"
>
> because the input length really *is* limited once you skip leading
> zeroes (and whatever base marker we have). We might have at most a
> 64-bit value in octal, so 22 bytes max.
>
> But I guess just changing the two GFP_KERNEL's to GFP_ATOMIC is much simpler.
>
>                 Linus