6.18-stable review patch. If anyone has any objections, please let me know.
------------------
From: Eric Dumazet edumazet@google.com
[ Upstream commit db5b4e39c4e63700c68a7e65fc4e1f1375273476 ]
Over the years, syzbot found many ways to crash the kernel in ip6gre_header() [1].
This involves team or bonding drivers ability to dynamically change their dev->needed_headroom and/or dev->hard_header_len
In this particular crash mld_newpack() allocated an skb with a too small reserve/headroom, and by the time mld_sendpack() was called, syzbot managed to attach an ip6gre device.
[1] skbuff: skb_under_panic: text:ffffffff8a1d69a8 len:136 put:40 head:ffff888059bc7000 data:ffff888059bc6fe8 tail:0x70 end:0x6c0 dev:team0 ------------[ cut here ]------------ kernel BUG at net/core/skbuff.c:213 ! <TASK> skb_under_panic net/core/skbuff.c:223 [inline] skb_push+0xc3/0xe0 net/core/skbuff.c:2641 ip6gre_header+0xc8/0x790 net/ipv6/ip6_gre.c:1371 dev_hard_header include/linux/netdevice.h:3436 [inline] neigh_connected_output+0x286/0x460 net/core/neighbour.c:1618 neigh_output include/net/neighbour.h:556 [inline] ip6_finish_output2+0xfb3/0x1480 net/ipv6/ip6_output.c:136 __ip6_finish_output net/ipv6/ip6_output.c:-1 [inline] ip6_finish_output+0x234/0x7d0 net/ipv6/ip6_output.c:220 NF_HOOK_COND include/linux/netfilter.h:307 [inline] ip6_output+0x340/0x550 net/ipv6/ip6_output.c:247 NF_HOOK+0x9e/0x380 include/linux/netfilter.h:318 mld_sendpack+0x8d4/0xe60 net/ipv6/mcast.c:1855 mld_send_cr net/ipv6/mcast.c:2154 [inline] mld_ifc_work+0x83e/0xd60 net/ipv6/mcast.c:2693
Fixes: c12b395a4664 ("gre: Support GRE over IPv6") Reported-by: syzbot+43a2ebcf2a64b1102d64@syzkaller.appspotmail.com Closes: https://lore.kernel.org/netdev/693b002c.a70a0220.33cd7b.0033.GAE@google.com/... Signed-off-by: Eric Dumazet edumazet@google.com Link: https://patch.msgid.link/20251211173550.2032674-1-edumazet@google.com Signed-off-by: Paolo Abeni pabeni@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- net/ipv6/ip6_gre.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/net/ipv6/ip6_gre.c b/net/ipv6/ip6_gre.c index c82a75510c0e..8bc3f05f594e 100644 --- a/net/ipv6/ip6_gre.c +++ b/net/ipv6/ip6_gre.c @@ -1366,9 +1366,16 @@ static int ip6gre_header(struct sk_buff *skb, struct net_device *dev, { struct ip6_tnl *t = netdev_priv(dev); struct ipv6hdr *ipv6h; + int needed; __be16 *p;
- ipv6h = skb_push(skb, t->hlen + sizeof(*ipv6h)); + needed = t->hlen + sizeof(*ipv6h); + if (skb_headroom(skb) < needed && + pskb_expand_head(skb, HH_DATA_ALIGN(needed - skb_headroom(skb)), + 0, GFP_ATOMIC)) + return -needed; + + ipv6h = skb_push(skb, needed); ip6_flow_hdr(ipv6h, 0, ip6_make_flowlabel(dev_net(dev), skb, t->fl.u.ip6.flowlabel, true, &t->fl.u.ip6));