linux-kernel - Re: bug reading /proc/sys/kernel/*: only first byte read.

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Message-ID: <20070130140015.GA123@tv-sign.ru>
Date:	Tue, 30 Jan 2007 17:00:15 +0300
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Andrew Morton <akpm@...l.org>
Cc:	Michael Tokarev <mjt@....msk.ru>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: bug reading /proc/sys/kernel/*: only first byte read.

On 01/30, Oleg Nesterov wrote:
>
> On 01/30, Andrew Morton wrote:
> >
> > +			if (len + pos < maxlen) {
>                         ^^^^^^^^^^^^^^^^^^^^^^^
> Shouldn't this be
> 			if (len < *lenp)
> 
> ?

On the other hand. If we may assume that original code was correct,
we can make a simpler patch?

Signed-off-by: Oleg Nesterov <oleg@...sign.ru>

--- 6.19/kernel/sysctl.c~	2006-11-17 19:42:31.000000000 +0300
+++ 6.19/kernel/sysctl.c	2007-01-30 16:46:00.000000000 +0300
@@ -1683,13 +1683,12 @@ static int _proc_do_string(void* data, i
 	size_t len;
 	char __user *p;
 	char c;
-	
-	if (!data || !maxlen || !*lenp ||
-	    (*ppos && !write)) {
+
+	if (!data || !maxlen || !*lenp) {
 		*lenp = 0;
 		return 0;
 	}
-	
+
 	if (write) {
 		len = 0;
 		p = buffer;
@@ -1710,6 +1709,15 @@ static int _proc_do_string(void* data, i
 		len = strlen(data);
 		if (len > maxlen)
 			len = maxlen;
+
+		if (*ppos > len) {
+			*lenp = 0;
+			return 0;
+		}
+
+		data += *ppos;
+		len  -= *ppos;
+
 		if (len > *lenp)
 			len = *lenp;
 		if (len)

-
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