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@rasmusvillemoes.dk>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/dev.c b/net/core/dev.c
index 658337bf33e437773ef81359746068043481b579..1a5d31fdea273ad5a454a73a3b009b6a97151b9f 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1064,7 +1064,7 @@ 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