linux-kernel - Re: [PATCH] autofs4: fix 32-bit userspace vs 64-bit kernel communications

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Date:	Wed, 11 Jun 2008 20:32:59 +0800
From:	Ian Kent <raven@...maw.net>
To:	Pavel Emelyanov <xemul@...nvz.org>
Cc:	autofs mailing list <autofs@...ux.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Konstantin Khlebnikov <khlebnikov@...nvz.org>
Subject: Re: [PATCH] autofs4: fix 32-bit userspace vs 64-bit kernel
	communications


On Wed, 2008-06-11 at 13:54 +0400, Pavel Emelyanov wrote:
> From: Konstantin Khlebnikov <khlebnikov@...nvz.org>
> 
> The struct autofs_v5_packet has only one difference between
> 32-bit and 64-bit versions - on 64-bit gcc aligns its size and
> it is 4 bytes larger that it is on 32-bit kernel. This confuses
> 32-bit user-space daemon, when talking to 64-bit kernel.

No, I don't think that's quite right.

As far as I know this issue arises when a user space program, compiled
as a 32-bit application is executed within 64-bit user space.

> 
> This is very critical for containerized setups, when containers
> with <different>-bit tolls are used.

Have you tested different situations with this change?
Will this affect the existing check and adjustment the version 5
automount daemon does now?

> 
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@...nvz.org>
> Acked-by: Pavel Emelyanov <xemul@...nvz.org>
> 
> ---
> 
> diff --git a/fs/autofs4/waitq.c b/fs/autofs4/waitq.c
> index 1e4a539..9855b6e 100644
> --- a/fs/autofs4/waitq.c
> +++ b/fs/autofs4/waitq.c
> @@ -132,6 +132,14 @@ static void autofs4_notify_daemon(struct autofs_sb_info *sbi,
>  		struct autofs_v5_packet *packet = &pkt.v5_pkt.v5_packet;
>  
>  		pktsz = sizeof(*packet);
> +#if defined(CONFIG_X86_64) && defined(CONFIG_IA32_EMULATION)
> +		/*
> +		 * On x86_64 autofs_v5_packet struct is padded with 4 bytes
> +		 * which breaks 32-bit autofs daemon.
> +		 */
> +		if (test_thread_flag(TIF_IA32))
> +			pktsz -= 4;
> +#endif
>  
>  		packet->wait_queue_token = wq->wait_queue_token;
>  		packet->len = wq->len;
> 

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