From: Greg Kroah-Hartman Date: Tue, 21 Apr 2026 13:16:33 +0000 (+0200) Subject: ipv6: rpl: reserve mac_len headroom when recompressed SRH grows X-Git-Tag: v7.1-rc2~22^2~34 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=9e6bf146b55999a095bb14f73a843942456d1adc;p=thirdparty%2Fkernel%2Flinux.git ipv6: rpl: reserve mac_len headroom when recompressed SRH grows ipv6_rpl_srh_rcv() decompresses an RFC 6554 Source Routing Header, swaps the next segment into ipv6_hdr->daddr, recompresses, then pulls the old header and pushes the new one plus the IPv6 header back. The recompressed header can be larger than the received one when the swap reduces the common-prefix length the segments share with daddr (CmprI=0, CmprE>0, seg[0][0] != daddr[0] gives the maximum +8 bytes). pskb_expand_head() was gated on segments_left == 0, so on earlier segments the push consumed unchecked headroom. Once skb_push() leaves fewer than skb->mac_len bytes in front of data, skb_mac_header_rebuild()'s call to: skb_set_mac_header(skb, -skb->mac_len); will store (data - head) - mac_len into the u16 mac_header field, which wraps to ~65530, and the following memmove() writes mac_len bytes ~64KiB past skb->head. A single AF_INET6/SOCK_RAW/IPV6_HDRINCL packet over lo with a two segment type-3 SRH (CmprI=0, CmprE=15) reaches headroom 8 after one pass; KASAN reports a 14-byte OOB write in ipv6_rthdr_rcv. Fix this by expanding the head whenever the remaining room is less than the push size plus mac_len, and request that much extra so the rebuilt MAC header fits afterwards. Fixes: 8610c7c6e3bd ("net: ipv6: add support for rpl sr exthdr") Cc: stable Reported-by: Anthropic Signed-off-by: Greg Kroah-Hartman Link: https://patch.msgid.link/2026042133-gout-unvented-1bd9@gregkh Signed-off-by: Jakub Kicinski --- diff --git a/net/ipv6/exthdrs.c b/net/ipv6/exthdrs.c index 95558fd6f447..03cbce842c1a 100644 --- a/net/ipv6/exthdrs.c +++ b/net/ipv6/exthdrs.c @@ -491,6 +491,7 @@ static int ipv6_rpl_srh_rcv(struct sk_buff *skb) struct net *net = dev_net(skb->dev); struct inet6_dev *idev; struct ipv6hdr *oldhdr; + unsigned int chdr_len; unsigned char *buf; int accept_rpl_seg; int i, err; @@ -592,8 +593,10 @@ looped_back: skb_pull(skb, ((hdr->hdrlen + 1) << 3)); skb_postpull_rcsum(skb, oldhdr, sizeof(struct ipv6hdr) + ((hdr->hdrlen + 1) << 3)); - if (unlikely(!hdr->segments_left)) { - if (pskb_expand_head(skb, sizeof(struct ipv6hdr) + ((chdr->hdrlen + 1) << 3), 0, + chdr_len = sizeof(struct ipv6hdr) + ((chdr->hdrlen + 1) << 3); + if (unlikely(!hdr->segments_left || + skb_headroom(skb) < chdr_len + skb->mac_len)) { + if (pskb_expand_head(skb, chdr_len + skb->mac_len, 0, GFP_ATOMIC)) { __IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)), IPSTATS_MIB_OUTDISCARDS); kfree_skb(skb); @@ -603,7 +606,7 @@ looped_back: oldhdr = ipv6_hdr(skb); } - skb_push(skb, ((chdr->hdrlen + 1) << 3) + sizeof(struct ipv6hdr)); + skb_push(skb, chdr_len); skb_reset_network_header(skb); skb_mac_header_rebuild(skb); skb_set_transport_header(skb, sizeof(struct ipv6hdr));