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Linux 2.0.33 vulnerability: oversized packets
From: lcamtuf () BOSS STASZIC WAW PL (Michal Zalewski)
Date: Fri, 17 Apr 1998 17:21:25 +0200


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--8323328-871852648-892826485=:211
Content-Type: TEXT/PLAIN; charset=US-ASCII

I'm not sure if it's known, but I haven't found anything about it.
No matter, there's something strange in net/ipv4/ip_fragment.h (it's
probably Alan's fault):

[ in function ip_glue ]

if(len>65535)
{
        printk("Oversized IP packet from %s.\n", in_ntoa(qp->iph->saddr));
        ip_statistics.IpReasmFails++;
        ip_free(qp);
        return NULL;
}

Right, printk with no NETDEBUG nor anything else. So, there's potential
DoS attack - I wrote simple exploit by modyfying teardrop source (mainly,
fragmentation offset of second packet = 0xFFFF), and it's quite nasty (see
attachment).

Fix:

--- ip_fragment.c.orig  Fri Apr 17 16:42:38 1998
+++ ip_fragment.c       Fri Apr 17 17:17:15 1998
@@ -345,7 +345,7 @@

        if(len>65535)
        {
-               printk("Oversized IP packet from %s.\n", in_ntoa(qp->iph->saddr));
+               NETDEBUG(printk("Oversized IP packet from %s.\n", in_ntoa(qp->iph->saddr)));
                ip_statistics.IpReasmFails++;
                ip_free(qp);
                return NULL;


_______________________________________________________________________
Michal Zalewski [lcamtuf () boss staszic waw pl] <= finger for pub PGP key
Iterowac jest rzecza ludzka, wykonywac rekursywnie - boska [P. Deutsch]
[echo "\$0&\$0">_;chmod +x _;./_] <=------=> [tel +48 (0) 22 813 25 86]

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