netdev - [patch] net/sched: potential data corruption

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Message-ID: <20100713132152.GL5658@bicker>
Date:	Tue, 13 Jul 2010 15:21:52 +0200
From:	Dan Carpenter <error27@...il.com>
To:	Jamal Hadi Salim <hadi@...erus.ca>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Stephen Hemminger <shemminger@...tta.com>,
	netdev@...r.kernel.org, kernel-janitors@...r.kernel.org,
	matthew@....cx
Subject: [patch] net/sched: potential data corruption

The reset_policy() does:
        memset(d->tcfd_defdata, 0, SIMP_MAX_DATA);
        strlcpy(d->tcfd_defdata, defdata, SIMP_MAX_DATA);

In the original code, the size of d->tcfd_defdata wasn't fixed and if
strlen(defdata) was less than 31, reset_policy() would cause memory
corruption.

Please Note:  The original alloc_defdata() assumes defdata is 32
characters and a NUL terminator while reset_policy() assumes defdata is
31 characters and a NUL.  This patch updates alloc_defdata() to match
reset_policy() (ie a shorter string).  I'm not very familiar with this
code so please review carefully.

Signed-off-by: Dan Carpenter <error27@...il.com>

diff --git a/net/sched/act_simple.c b/net/sched/act_simple.c
index 1b4bc69..4a1d640 100644
--- a/net/sched/act_simple.c
+++ b/net/sched/act_simple.c
@@ -73,10 +73,10 @@ static int tcf_simp_release(struct tcf_defact *d, int bind)
 
 static int alloc_defdata(struct tcf_defact *d, char *defdata)
 {
-	d->tcfd_defdata = kstrndup(defdata, SIMP_MAX_DATA, GFP_KERNEL);
+	d->tcfd_defdata = kzalloc(SIMP_MAX_DATA, GFP_KERNEL);
 	if (unlikely(!d->tcfd_defdata))
 		return -ENOMEM;
-
+	strlcpy(d->tcfd_defdata, defdata, SIMP_MAX_DATA);
 	return 0;
 }
 
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