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

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Date:	Sun, 31 Aug 2008 00:04:23 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Vegard Nossum <vegard.nossum@...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

[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;
| 
| 
| Vegard

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)

| 
| -- 
| "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
| 
		- Cyrill -
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