netdev - [PATCH 1/7] net: core: improve sanity checking in __dev_alloc

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Message-Id: <20171112231511.4666-2-linux@rasmusvillemoes.dk>
Date:   Mon, 13 Nov 2017 00:15:04 +0100
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     "David S. Miller" <davem@...emloft.net>
Cc:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 1/7] net: core: improve sanity checking in __dev_alloc_name

__dev_alloc_name is called from the public (and exported)
dev_alloc_name(), so we don't have a guarantee that strlen(name) is at
most IFNAMSIZ. If somebody manages to get __dev_alloc_name called with a
% char beyond the 31st character, we'd be making a snprintf() call that
will very easily crash the kernel (using an appropriate %p extension,
we'll likely dereference some completely bogus pointer).

In the normal case where strlen() is sane, we don't even save anything
by limiting to IFNAMSIZ, so just use strchr().

Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
---
 net/core/dev.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 11596a302a26..87e19804757b 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1062,7 +1062,7 @@ static int __dev_alloc_name(struct net *net, const char *name, char *buf)
 	unsigned long *inuse;
 	struct net_device *d;

-	p = strnchr(name, IFNAMSIZ-1, '%');
+	p = strchr(name, '%');
 	if (p) {
 		/*
 		 * Verify the string as this thing may have come from
-- 
2.11.0