CVE-2026-46260

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

ipv6: Fix out-of-bound access in fib6addrt2node().

syzbot reported out-of-bound read in fib6addrt2node(). [0]

When IPv6 route is created with RTANHID, struct fib6info does not have the trailing struct fib6nh.

The cited commit started to check !iter->fib6nh->fibnhgwfamily to ensure that rt6qualifyfor_ecmp() will return false for iter.

If iter->nh is not NULL, rt6qualifyfor_ecmp() returns false anyway.

Let's check iter->nh before reading iter->fib6_nh and avoid OOB read.

Read of size 1 at addr ffff8880384ba6de by task syz.0.18/5500

CPU: 0 UID: 0 PID: 5500 Comm: syz.0.18 Not tainted syzkaller #0 PREEMPT(full) Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 Call Trace: <TASK> dumpstacklvl+0xe8/0x150 lib/dumpstack.c:120 printaddressdescription mm/kasan/report.c:378 [inline] printreport+0xba/0x230 mm/kasan/report.c:482 kasanreport+0x117/0x150 mm/kasan/report.c:595 fib6addrt2node+0x349c/0x3500 net/ipv6/ip6fib.c:1142 fib6addrt2nodenh net/ipv6/ip6fib.c:1363 [inline] fib6add+0x910/0x18c0 net/ipv6/ip6fib.c:1531 __ip6insrt net/ipv6/route.c:1351 [inline] ip6routeadd+0xde/0x1b0 net/ipv6/route.c:3957 inet6rtmnewroute+0x268/0x19e0 net/ipv6/route.c:5660 rtnetlinkrcvmsg+0x7d5/0xbe0 net/core/rtnetlink.c:6958 netlinkrcvskb+0x232/0x4b0 net/netlink/afnetlink.c:2550 netlinkunicastkernel net/netlink/afnetlink.c:1318 [inline] netlinkunicast+0x80f/0x9b0 net/netlink/afnetlink.c:1344 netlinksendmsg+0x813/0xb40 net/netlink/afnetlink.c:1894 socksendmsgnosec net/socket.c:727 [inline] __sock_sendmsg net/socket.c:742 [inline] ____sys_sendmsg+0xa68/0xad0 net/socket.c:2592 ___sys_sendmsg+0x2a5/0x360 net/socket.c:2646 __sys_sendmsg net/socket.c:2678 [inline] __dosyssendmsg net/socket.c:2683 [inline] __sesyssendmsg net/socket.c:2681 [inline] _x64syssendmsg+0x1bd/0x2a0 net/socket.c:2681 dosyscallx64 arch/x86/entry/syscall64.c:63 [inline] dosyscall64+0xe2/0xf80 arch/x86/entry/syscall64.c:94 entrySYSCALL64afterhwframe+0x77/0x7f RIP: 0033:0x7f9316b9aeb9 Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007ffd8809b678 EFLAGS: 00000246 ORIGRAX: 000000000000002e RAX: ffffffffffffffda RBX: 00007f9316e15fa0 RCX: 00007f9316b9aeb9 RDX: 0000000000000000 RSI: 0000200000004380 RDI: 0000000000000003 RBP: 00007f9316c08c1f R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007f9316e15fac R14: 00007f9316e15fa0 R15: 00007f9316e15fa0 </TASK>

Allocated by task 5499: kasansavestack mm/kasan/common.c:57 [inline] kasansavetrack+0x3e/0x80 mm/kasan/common.c:78 poisonkmallocredzone mm/kasan/common.c:398 [inline] __kasankmalloc+0x93/0xb0 mm/kasan/common.c:415 kasankmalloc include/linux/kasan.h:263 [inline] __dokmallocnode mm/slub.c:5657 [inline] __kmallocnoprof+0x40c/0x7e0 mm/slub.c:5669 kmallocnoprof include/linux/slab.h:961 [inline] kzallocnoprof include/linux/slab.h:1094 [inline] fib6info_alloc+0x30/0xf0 net/ipv6/ip6fib.c:155 ip6routeinfocreate+0x142/0x860 net/ipv6/route.c:3820 ip6routeadd+0x49/0x1b0 net/ipv6/route.c:3949 inet6rtmnewroute+0x268/0x19e0 net/ipv6/route.c:5660 rtnetlinkrcvmsg+0x7d5/0xbe0 net/core/rtnetlink.c:6958 netlinkrcvskb+0x232/0x4b0 net/netlink/afnetlink.c:2550 netlinkunicastkernel net/netlink/afnetlink.c:1318 [inline] netlinkunicast+0x80f/0x9b0 net/netlink/afnetlink.c:1344 netlinksendmsg+0x813/0xb40 net/netlink/afnetlink.c:1894 socksendmsgnosec net/socket.c:727 [inline] __sock_sendmsg net/socket.c:742 [inline] ____sys_sendmsg+0xa68/0xad0 net/socket.c:2592 __syss ---truncated---