sunrpc: fix possible overrun on read of /proc/sys/sunrpc/transports

Vegard Nossum reported
----------------------
> 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.

David Wagner added (among other things) that copy_to_user could be
probably used here.

Ingo Oeser suggested to use simple_read_from_buffer() here.

The conclusion is that proc_do_xprt doesn't check for userside buffer
size indeed so fix this by using Ingo's suggestion.

Reported-by: Vegard Nossum <vegard.nossum@gmail.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
CC: Ingo Oeser <ioe-lkml@rameria.de>
Cc: Neil Brown <neilb@suse.de>
Cc: Chuck Lever <chuck.lever@oracle.com>
Cc: Greg Banks <gnb@sgi.com>
Cc: Tom Tucker <tom@opengridcomputing.com>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>

diff --git a/net/sunrpc/sysctl.c b/net/sunrpc/sysctl.c
index 0f8c439b848a1eab04f0f21f2ea763863e424b2f..5231f7aaac0e483ebb8b457c3c6e2218464da409 100644 (file)
--- a/net/sunrpc/sysctl.c
+++ b/net/sunrpc/sysctl.c
@@ -60,24 +60,14 @@ static int proc_do_xprt(ctl_table *table, int write, struct file *file,
                        void __user *buffer, size_t *lenp, loff_t *ppos)
 {
        char tmpbuf[256];
-       int len;
+       size_t len;
+
        if ((*ppos && !write) || !*lenp) {
                *lenp = 0;
                return 0;
        }
-       if (write)
-               return -EINVAL;
-       else {
-               len = svc_print_xprts(tmpbuf, sizeof(tmpbuf));
-               if (!access_ok(VERIFY_WRITE, buffer, len))
-                       return -EFAULT;
-
-               if (__copy_to_user(buffer, tmpbuf, len))
-                       return -EFAULT;
-       }
-       *lenp -= len;
-       *ppos += len;
-       return 0;
+       len = svc_print_xprts(tmpbuf, sizeof(tmpbuf));
+       return simple_read_from_buffer(buffer, *lenp, ppos, tmpbuf, len);
 }
 
 static int