[Devel] [PATCH] autofs: fix autofs_v5_packet structure for compat mode

[Dmitry V. Levin]

On Thu, Aug 31, 2017 at 02:11:34PM +0400, Stanislav Kinsburskiy wrote:
> Due to integer variables alignment size of struct autofs_v5_packet in 300
> bytes in 32-bit architectures (instead of 304 bytes in 64-bits architectures).
> 
> This may lead to memory corruption (64 bits kernel always send 304 bytes,
> while 32-bit userspace application expects for 300).
> 
> https://jira.sw.ru/browse/PSBM-71078
> 
> Signed-off-by: Stanislav Kinsburskiy <skinsbursky at virtuozzo.com>
> ---
>  include/uapi/linux/auto_fs4.h |    2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/include/uapi/linux/auto_fs4.h b/include/uapi/linux/auto_fs4.h
> index e02982f..8729a47 100644
> --- a/include/uapi/linux/auto_fs4.h
> +++ b/include/uapi/linux/auto_fs4.h
> @@ -137,6 +137,8 @@ struct autofs_v5_packet {
>  	__u32 pid;
>  	__u32 tgid;
>  	__u32 len;
> +	__u32 blob;		/* This is needed to align structure up to 8
> +				   bytes for ALL archs including 32-bit */
>  	char name[NAME_MAX+1];
>  };

This change breaks ABI because it changes offsetof(struct autofs_v5_packet, name).
If you need to fix the alignment, use  __attribute__((aligned(8))).

An alignment change would also be an ABI breakage on 32-bit architectures,
though.


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