UBUNTU-CVE-2026-97974: Medium severity ubuntu/linux-hwe-edge vulnerability

In the Linux kernel, the following vulnerability has been resolved: ipv6: null-check fib6node before accessing in ip6delrtsiblings() syzbot reported a null-ptr-deref in ip6delrtsiblings() [0]. The stack trace hinted towards a null dereference of rt->fib6node when fn->leaf is accessed in ip6delrtsiblings(). With RTNLFLAGDOITUNLOCKED set, inet6rtmdelroute() operations run concurrently without acquiring the RTNL lock. In ip6routedel(), the route lookup happens under rcureadlock() without acquiring table->tb6lock. Between ip6routedel() looking up the route and ip6delrtsiblings() acquiring table->tb6lock, another thread can modify the routing table. For example, when an ECMP route is replaced via RTMNEWROUTE with NLMFREPLACE, fib6addrt2node() unlinks all old siblings and sets iter->fib6node = NULL. A reproducer was found that triggers this [1]. Add a check to ensure rt->fib6node is non-null before accessing it. [0] KASAN: null-ptr-deref in range [0x0000000000000020-0x0000000000000027] RIP: 0010:ip6delrtsiblings+0x31e/0x7c0 net/ipv6/route.c:4056 Call Trace: <TASK> ip6routedel+0x1054/0x1110 net/ipv6/route.c:4232 inet6rtmdelroute+0x5d7/0x6d0 net/ipv6/route.c:5669 rtnetlinkrcvmsg+0x802/0xc00 net/core/rtnetlink.c:7132 netlinkrcvskb+0x226/0x4a0 net/netlink/afnetlink.c:2556 netlinkunicastkernel net/netlink/afnetlink.c:1319 [inline] netlinkunicast+0x7f5/0x990 net/netlink/afnetlink.c:1345 netlinksendmsg+0x813/0xb40 net/netlink/afnetlink.c:1900 socksendmsgnosec+0x13a/0x180 net/socket.c:800 socksendmsg net/socket.c:815 [inline] syssendmsg+0x565/0x870 net/socket.c:2713 syssendmsg+0x2a5/0x360 net/socket.c:2767 syssendmsg net/socket.c:2799 [inline] dosyssendmsg net/socket.c:2804 [inline] sesyssendmsg net/socket.c:2802 [inline] x64syssendmsg+0x1b7/0x290 net/socket.c:2802 dosyscallx64 arch/x86/entry/syscall64.c:61 [inline] dosyscall64+0x166/0x520 arch/x86/entry/syscall64.c:84 entrySYSCALL64afterhwframe+0x77/0x7f </TASK> [1] https://gist.github.com/NamanGulati/0766a1159b6ca61928faaf87425ff899