CVE-2026-98934: ipv6: sr: use skb_get_hash_net() in seg6_make_flowlabel()

In the Linux kernel, the following vulnerability has been resolved:

ipv6: sr: use skbgethashnet() in seg6makeflowlabel()

Since commit d58e468b1112 ("flowdissector: implements flow dissector BPF hook") skbflowdissect() needs a net pointer, either from skb->dev, skb->sk, or since commit 3cbf4ffba5ee ("net: plumb network namespace into skbflowdissect") a caller provided pointer.

syzbot was able to reach seg6makeflowlabel() with an skb having neither skb->dev nor skb->sk set: a TIPC UDP bearer sends a discovery message through an IPv4 route using seg6 encap, while net.ipv6.seg6flowlabel is set to 1.

seg6makeflowlabel() already has a net pointer, use skbgethashnet().

WARNING: net/core/flowdissector.c:1131 at skbflowdissect+0x910/0x5368 net/core/flowdissector.c:1126, CPU#0: syz.0.17/4930 Call trace: skbflowdissect+0x910/0x5368 net/core/flowdissector.c:1126 (P) skbgethashnet+0xe0/0x29c net/core/flowdissector.c:1903 skbgethash include/linux/skbuff.h:1663 [inline] seg6makeflowlabel+0xcc/0x1ec net/ipv6/seg6iptunnel.c:132 seg6dosrhencap+0x320/0xbf4 net/ipv6/seg6iptunnel.c:161 seg6dosrh+0x4b4/0xa44 net/ipv6/seg6iptunnel.c:431 seg6outputcore+0x164/0x688 net/ipv6/seg6iptunnel.c:681 seg6output+0x44/0x1ac net/ipv6/seg6iptunnel.c:744 lwtunneloutput+0x3d0/0x664 net/core/lwtunnel.c:356 dstoutput include/net/dst.h:470 [inline] iplocalout+0x110/0x148 net/ipv4/ipoutput.c:131 iptunnelxmit+0x50c/0xd38 net/ipv4/iptunnelcore.c:97 udptunnelxmitskb+0x220/0x348 net/ipv4/udptunnelcore.c:187 tipcudpxmit+0x75c/0x9c0 net/tipc/udpmedia.c:202 tipcudpsendmsg+0x214/0x374 net/tipc/udpmedia.c:274 tipcbearerxmitskb+0x260/0x3b0 net/tipc/bearer.c:576 tipcenablebearer net/tipc/bearer.c:366 [inline] tipcnlbearerenable+0xc90/0xfb0 net/tipc/bearer.c:1048 tipcnlbearerenable+0x2c/0x48 net/tipc/bearer.c:1057 genlfamilyrcvmsgdoit+0x1e4/0x2d4 net/netlink/genetlink.c:1114