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Linux ip6gre_err invalid reads

Posted on 30 November -0001

<HTML><HEAD><TITLE>Linux ip6gre_err() invalid reads</TITLE><META http-equiv="Content-Type" content="text/html; charset=utf-8"></HEAD><BODY>Andrey Konovalov reported out of bound accesses in ip6gre_err() If GRE flags contains GRE_KEY, the following expression *(((__be32 *)p) + (grehlen / 4) - 1) accesses data ~40 bytes after the expected point, since grehlen includes the size of IPv6 headers. Let's use a "struct gre_base_hdr *greh" pointer to make this code more readable. p[1] becomes greh->protocol. grhlen is the GRE header length. +++ b/net/ipv6/ip6_gre.c @@ -367,35 +367,37 @@ static void ip6gre_tunnel_uninit(struct net_device *dev) static void ip6gre_err(struct sk_buff *skb, struct inet6_skb_parm *opt, - u8 type, u8 code, int offset, __be32 info) + u8 type, u8 code, int offset, __be32 info) { - const struct ipv6hdr *ipv6h = (const struct ipv6hdr *)skb->data; - __be16 *p = (__be16 *)(skb->data + offset); - int grehlen = offset + 4; + const struct gre_base_hdr *greh; + const struct ipv6hdr *ipv6h; + int grehlen = sizeof(*greh); struct ip6_tnl *t; + int key_off = 0; __be16 flags; + __be32 key; - flags = p[0]; - if (flags&(GRE_CSUM|GRE_KEY|GRE_SEQ|GRE_ROUTING|GRE_VERSION)) { - if (flags&(GRE_VERSION|GRE_ROUTING)) - return; - if (flags&GRE_KEY) { - grehlen += 4; - if (flags&GRE_CSUM) - grehlen += 4; - } + if (!pskb_may_pull(skb, offset + grehlen)) + return; + greh = (const struct gre_base_hdr *)(skb->data + offset); + flags = greh->flags; + if (flags & (GRE_VERSION | GRE_ROUTING)) + return; + if (flags & GRE_CSUM) + grehlen += 4; + if (flags & GRE_KEY) { + key_off = grehlen + offset; + grehlen += 4; } - /* If only 8 bytes returned, keyed message will be dropped here */ - if (!pskb_may_pull(skb, grehlen)) + if (!pskb_may_pull(skb, offset + grehlen)) return; ipv6h = (const struct ipv6hdr *)skb->data; - p = (__be16 *)(skb->data + offset); + greh = (const struct gre_base_hdr *)(skb->data + offset); + key = key_off ? *(__be32 *)(skb->data + key_off) : 0; t = ip6gre_tunnel_lookup(skb->dev, &ipv6h->daddr, &ipv6h->saddr, - flags & GRE_KEY ? - *(((__be32 *)p) + (grehlen / 4) - 1) : 0, - p[1]); + key, greh->protocol); if (!t) return; </BODY></HTML>

 

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