Vegard Nossum reported

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>
---

Index: linux-2.6.git/net/sunrpc/sysctl.c
===================================================================
--- linux-2.6.git.orig/net/sunrpc/sysctl.c	2008-08-31 18:58:50.000000000 +0400
+++ linux-2.6.git/net/sunrpc/sysctl.c	2008-08-31 19:15:57.000000000 +0400
@@ -60,23 +60,27 @@ static int proc_do_xprt(ctl_table *table
 			void __user *buffer, size_t *lenp, loff_t *ppos)
 {
 	char tmpbuf[256];
-	int len;
+	size_t len;
+	ssize_t ret;
+
 	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;
+		ret = simple_read_from_buffer(buffer, *lenp, ppos,
+						tmpbuf, len);
+		if (ret >= 0) {
+			*lenp = ret;
+			ret = 0;
+		}
+		return ret;
 	}
-	*lenp -= len;
-	*ppos += len;
+
 	return 0;
 }
 
--

[ message continues ]

Thanks for fixing this!  And apologies for not looking closer when this
first went in....


The only caller of .proc_handler appears to be
fs/proc/proc_sysctl.c:proc_sys_call_handler(), which checks permissions
before calling us, so we'll never hit this case (since "transports" is


And it looks to me like the proc_sys_call_handler doesn't use *lenp when

That gives the following:

--b.


commit 20d0daba667a355e7c76362633423ab569d2193d
Author: Cyrill Gorcunov <gorcunov@gmail.com>
Date:   Sun Aug 31 19:25:49 2008 +0400

    sunrpc - fixup userspace buffer possible overrun v3
    
    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>
    Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>

diff --git a/net/sunrpc/sysctl.c b/net/sunrpc/sysctl.c
index 0f8c439..5231f7a 100644
--- 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, ...
[ message continues ]

[J. Bruce Fields - Sun, Aug 31, 2008 at 09:17:09PM -0400]
...
| 
| That gives the following:
| 
| --b.
| 
...

Thanks Bruce

		- Cyrill -
--

[ message continues ]