linux-kernel - Re: binfmt

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Date:	Tue, 11 Jun 2013 10:17:16 +0800
From:	Jeff Chua <jeff.chua.linux@...il.com>
To:	Al Viro <viro@...iv.linux.org.uk>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: Re: binfmt_misc broken

On Tue, Jun 11, 2013 at 9:51 AM, Al Viro <viro@...iv.linux.org.uk> wrote:


> Patch is complete BS and I really wonder what kernel have you observed that bug on -
> with mainline on amd64 your example yields
> root@...-amd64:~# cat /proc/sys/fs/binfmt_misc/arm
> enabled
> interpreter /usr/bin/qemu-arm-static
> flags:
> offset 0
> magic 7f454c4601010100000000000000000002002800
> mask ffffffffffffff00fffffffffffffffffeffffff
>
> A reproducer, please...  As for the memcmp() Linus has suggested - it's !Magic case, i.e.
> what we are comparing there is not the file contents, it's the extension.  IOW, strcmp()
> is the right thing to use there - pathnames do not contain NULs in the middle...

BS ... yes, after testing it again, you may be right. Not intented, sorry.

I did another test with bash.

# bash -version
GNU bash, version 4.2.45(2)-release (x86_64-unknown-linux-gnu)

# echo ':arm:M::\x7fELF\x01\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x28\x00:\xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff\xff:/usr/bin/qemu-arm-static:'
:arm:M::ELF(:ÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿþÿÿÿ:/usr/bin/qemu-arm-static:

# echo ':arm:M::\\x7fELF\\x01\\x01\\x01\\x00\\x00\\x00\\x00\\x00\\x00\\x00\\x00\\x00\\x02\\x00\\x28\\x00:\\xff\\xff\\xff\\xff\\xff\\xff\\xff\\x00\\xff\\xff\\xff\\xff\\xff\\xff\\xff\\xff\\xfe\\xff\\xff\\xff:/usr/bin/qemu-arm-static:'
:arm:M::\x7fELF\x01\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x28\x00:\xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff\xff:/usr/bin/qemu-arm-static:

I supposed it's my bash configured with opt_xpg_echo=yes that's
sending in different data to the kernel.

Sending in the double-escape solved the problem. BS totally! My fault.

Thanks,
Jeff
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