Messages in this thread | | | Date | Sat, 30 Aug 2008 21:42:30 +0200 | From | "Vegard Nossum" <> | Subject | Re: buffer overflow in /proc/sys/sunrpc/transports |
| |
On Sat, Aug 30, 2008 at 9:06 PM, Cyrill Gorcunov <gorcunov@gmail.com> wrote: > [Vegard Nossum - Sat, Aug 30, 2008 at 08:44:22PM +0200] > | Hi, > | > | I noticed that something weird is going on with /proc/sys/sunrpc/transports. > | This file is generated in net/sunrpc/sysctl.c, function proc_do_xprt(). When > | I "cat" this file, I get the expected output: > | > | $ cat /proc/sys/sunrpc/transports > | tcp 1048576 > | udp 32768 > | > | But I think that it does not check the length of the buffer supplied by > | userspace to read(). With my original program, I found that the stack was > | being overwritten by the characters above, even when the length given to > | read() was just 1. So I have created a test program, see it at the bottom of > | this e-mail. Here is its output: > | > ... > > Indeed, maybe just add checking for user buffer length? > As proc_dodebug() in this file are doing. I don't think > the user would be happy with his stack burned :) > > Something like: > --- > > Index: linux-2.6.git/net/sunrpc/sysctl.c > =================================================================== > --- linux-2.6.git.orig/net/sunrpc/sysctl.c 2008-07-20 11:40:14.000000000 +0400 > +++ linux-2.6.git/net/sunrpc/sysctl.c 2008-08-30 23:05:30.000000000 +0400 > @@ -69,6 +69,8 @@ static int proc_do_xprt(ctl_table *table > return -EINVAL; > else { > len = svc_print_xprts(tmpbuf, sizeof(tmpbuf)); > + if (*lenp < len) > + return -EFAULT; > if (!access_ok(VERIFY_WRITE, buffer, len)) > return -EFAULT; > >
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?
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
| |