Messages in this thread | | | Date | Sat, 30 Aug 2008 23:45:55 +0400 | From | Cyrill Gorcunov <> | Subject | Re: buffer overflow in /proc/sys/sunrpc/transports |
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[Vegard Nossum - Sat, Aug 30, 2008 at 09:42:30PM +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; | > | > | | 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
Get me some time to check
| | -- | "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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