linux-kernel - Re: buffer overflow in /proc/sys/sunrpc/transports

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Date:	Sat, 30 Aug 2008 22:13:23 +0200
From:	"Vegard Nossum" <vegard.nossum@...il.com>
To:	"Cyrill Gorcunov" <gorcunov@...il.com>
Cc:	"Tom Tucker" <tom@...ngridcomputing.com>,
	"Neil Brown" <neilb@...e.de>,
	"Chuck Lever" <chuck.lever@...cle.com>, "Greg Banks" <gnb@....com>,
	"J. Bruce Fields" <bfields@...i.umich.edu>,
	linux-kernel@...r.kernel.org
Subject: Re: buffer overflow in /proc/sys/sunrpc/transports

On Sat, Aug 30, 2008 at 10:04 PM, Cyrill Gorcunov <gorcunov@...il.com> wrote:
> [Vegard Nossum - Sat, Aug 30, 2008 at 09:59:38PM +0200]
> | On Sat, Aug 30, 2008 at 9:56 PM, Cyrill Gorcunov <gorcunov@...il.com> wrote:
> | > | BTW, look at this:
> | > |
> | > |     $ od -A x -t x1z /proc/sys/sunrpc/transports
> | > |     000000 74 63 70 20 31 30 34 38 35 37 36 0a 75 64 70 20  >tcp 1048576.udp <
> | > |     000010 33 32 37 36 38 0a 00 00 00 00 00 00 00 00 00 00  >32768...........<
> | > |     000020 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  >................<
> | > |     *
> | > |     0003e0 00 00 00 00 00 00 00 00 00 00                    >..........<
> | > |     0003ea
> | > |
> | > | ...and:
> | > |
> | > |     $ strace -e trace=read cat /proc/sys/sunrpc/transports > /dev/null
> | > |     read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0@G\316E4\0\0\0"...,
> | > | 512) = 512
> | > |     read(3, "tcp 1048576\nudp 32768\n\0\0\0\0\0\0\0\0\0\0"..., 4096) = 4074
> | > |     read(3, "", 4096)                       = 0
> | > |
> | > | ...why does it have a huge return value? The output is only about 40
> | > | bytes... why add all the \0? Would your patch also fix this?
> | >
> | > I think it's from strace side - it pass 4096 zero'ed buffer.
> |
> | "cat" passed buffer of size 4096, yes. But read() still returned 4074.
> | It should have returned 38 or so.
> |
> | > At least I don't see additional issues from kernel side in buffer
> | > filling - except from svc_print_xprts() which walk over list.
> | > But I think sunpc guys should know details :)
> | > Will send short-fix patch soon :)
> |
> | It looks like it's returning (sizeof(buffer) - x) where it really
> | should be returning x. Maybe it's this one that should be different?
> |
> |         *lenp -= len;
> |
>
> yes, but this is just a side effect, if we fix main error - it should
> resolve this problem too. Did you try the fix I sent a few msgs ago?
> (I don't have sunrpc on my machine)

Sorry, I did it now :-)

    $ uname -a
    Linux grianne 2.6.27-rc5-00006-gbef69ea-dirty #4 SMP PREEMPT Sat
Aug 30 22:07:18 CEST 2008 i686 i686 i386 GNU/Linux

    $ strace -e trace=read cat /proc/sys/sunrpc/transports > /dev/null
    read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0\320
\265\0004\0\0\0"..., 512) = 512
    read(3, "tcp 1048576\nudp 32768\n\0\0\0\0\0\0\0\0\0\0"..., 4096) = 4074
    read(3, "", 4096)                       = 0

So that problem seems to remain.


Vegard

-- 
"The animistic metaphor of the bug that maliciously sneaked in while
the programmer was not looking is intellectually dishonest as it
disguises that the error is the programmer's own creation."
	-- E. W. Dijkstra, EWD1036
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