Messages in this thread | | | Date | Sat, 30 Aug 2008 23:23:24 +0400 | From | Cyrill Gorcunov <> | Subject | Re: buffer overflow in /proc/sys/sunrpc/transports |
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[Cyrill Gorcunov - Sat, Aug 30, 2008 at 11:21:12PM +0400] | [Vegard Nossum - Sat, Aug 30, 2008 at 09:15:16PM +0200] | | 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; | | > | | | | Hm. I think this is wrong. Shouldn't we copy as many bytes as the user | | indicated? | | Well, hard to say what user-space programmer is expecting from us. | I mean - maybe he (reader) wants only part of results not the whole | contents BUT by this way he never know what the whole conetnts would be | until trying to read more (ie to check if there no more data from | kernel side). What is preferred behaviour - i don't know :) | | | | | | | 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 | | | | - Cyrill -
Btw, I didn't try to get size of sysfs file - will such an action return size of data from kernel side?
- Cyrill -
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