From: Zhiling Zou <zhilinz@nebusec.ai> stable inclusion from stable-v6.6.157 commit defa0adeff132cc90ed66915b9a104d9393e1e54 category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/18891 CVE: CVE-2026-89563 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=... -------------------------------- commit 87f21b59ddc618eff9670c174842964ad65fdade upstream. ip6_tnl_xmit() may need to expand headroom before it can push the outer IPv6 and optional encap headers. It currently does that with skb_realloc_headroom(), copies skb->sk ownership, consumes the original skb, and then continues processing with the replacement skb kept only in its local variable. That is safe only if the helper cannot fail afterwards. But this helper still has post-reallocation error exits. collect_md tunnels reject non-NONE encap after the replacement, and ip6_tnl_encap() can also fail later. In those cases the helper returns an error to its callers while the caller still only has the original skb pointer. Both ip6_tnl_start_xmit() and the IPv6 GRE paths free the caller skb on error, so they can end up freeing an skb that ip6_tnl_xmit() already consumed. Use skb_cow_head() instead. It provides the required headroom and writability without privately replacing the caller-owned skb, so later error returns cannot leave callers with a stale pointer. The Ethernet users, ip6gretap and ip6erspan, clear IFF_TX_SKB_SHARING and already call skb_cow_head() before entering ip6_tnl_xmit(). They do not rely on the removed skb_shared() reallocation. This also makes the IPv6 tunnel path consistent with ip_tunnel_xmit(). Fixes: 058214a4d1df ("ip6_tun: Add infrastructure for doing encapsulation") Cc: stable@vger.kernel.org Reported-by: Vega <vega@nebusec.ai> Reviewed-by: Ido Schimmel <idosch@nvidia.com> Signed-off-by: Zhiling Zou <zhilinz@nebusec.ai> Link: https://patch.msgid.link/30807a062ccc5c9c8a5ec2c5eb805ef279c50bdd.1786452593... Signed-off-by: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: JiangJieHua <jiangjiehua1@huawei.com> --- net/ipv6/ip6_tunnel.c | 15 ++------------- 1 file changed, 2 insertions(+), 13 deletions(-) diff --git a/net/ipv6/ip6_tunnel.c b/net/ipv6/ip6_tunnel.c index dfabd9969b3f3..54193e3b5492c 100644 --- a/net/ipv6/ip6_tunnel.c +++ b/net/ipv6/ip6_tunnel.c @@ -1226,19 +1226,8 @@ int ip6_tnl_xmit(struct sk_buff *skb, struct net_device *dev, __u8 dsfield, */ max_headroom += LL_RESERVED_SPACE(tdev); - if (skb_headroom(skb) < max_headroom || skb_shared(skb) || - (skb_cloned(skb) && !skb_clone_writable(skb, 0))) { - struct sk_buff *new_skb; - - new_skb = skb_realloc_headroom(skb, max_headroom); - if (!new_skb) - goto tx_err_dst_release; - - if (skb->sk) - skb_set_owner_w(new_skb, skb->sk); - consume_skb(skb); - skb = new_skb; - } + if (skb_cow_head(skb, max_headroom)) + goto tx_err_dst_release; if (t->parms.collect_md) { if (t->encap.type != TUNNEL_ENCAP_NONE) -- 2.33.8