Subject: Re: [PATCH] drbd: Fix kernel_sendmsg() usage
To: Christoph Hellwig <hch@infradead.org>
References: <1478601789-15060-1-git-send-email-richard@nod.at>
 <20161108154924.GA19063@infradead.org>
Cc: drbd-dev@lists.linbit.com, linux-kernel@vger.kernel.org,
        lars.ellenberg@linbit.com, philipp.reisner@linbit.com,
        stable@vger.kernel.org, viro@zeniv.linux.org.uk,
        christoph.lechleitner@iteg.at, wolfgang.glas@iteg.at
From: Richard Weinberger <richard@nod.at>
Message-ID: <748300d8-2a47-b273-5458-014dd3e3d6fc@nod.at>
Date: Tue, 8 Nov 2016 17:02:57 +0100
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Christoph,

On 08.11.2016 16:49, Christoph Hellwig wrote:
> On Tue, Nov 08, 2016 at 11:43:09AM +0100, Richard Weinberger wrote:
>> Don't pass a size larger than iov_len to kernel_sendmsg().
>> Otherwise it will cause a NULL pointer deref when kernel_sendmsg()
>> returns with rv < size.
>>
>> Although the issue exists since day 0, only on non-ancient kernels
>> that contain change 57be5bdad759 ("ip: convert tcp_sendmsg() to iov_iter
>> primitives") it seems to trigger [0][1][2][3][4].
> 
> The real fix here is to convert it to the right primitive, e.g. take
> Al's patch from here:
> 
> https://git.kernel.org/cgit/linux/kernel/git/viro/vfs.git/commit/?h=work.sendmsg&id=7a4992299554a9e1ed3c4540bcfa9e40aa9a6376

Yes, I talked already with Al about this. He suggested to fix the size parameter
first such that back-porting to -stable is easy.

Thanks,
//richard