net: nexthop: don't allow empty NHA_GROUP
Currently the nexthop code will use an empty NHA_GROUP attribute, but it requires at least 1 entry in order to function properly. Otherwise we end up derefencing null or random pointers all over the place due to not having any nh_grp_entry members allocated, nexthop code relies on having at least the first member present. Empty NHA_GROUP doesn't make any sense so just disallow it. Also add a WARN_ON for any future users of nexthop_create_group(). BUG: kernel NULL pointer dereference, address: 0000000000000080 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 0 P4D 0 Oops: 0000 [#1] SMP CPU: 0 PID: 558 Comm: ip Not tainted 5.9.0-rc1+ #93 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-2.fc32 04/01/2014 RIP: 0010:fib_check_nexthop+0x4a/0xaa Code: 0f 84 83 00 00 00 48 c7 02 80 03 f7 81 c3 40 80 fe fe 75 12 b8 ea ff ff ff 48 85 d2 74 6b 48 c7 02 40 03 f7 81 c3 48 8b 40 10 <48> 8b 80 80 00 00 00 eb 36 80 78 1a 00 74 12 b8 ea ff ff ff 48 85 RSP: 0018:ffff88807983ba00 EFLAGS: 00010213 RAX: 0000000000000000 RBX: ffff88807983bc00 RCX: 0000000000000000 RDX: ffff88807983bc00 RSI: 0000000000000000 RDI: ffff88807bdd0a80 RBP: ffff88807983baf8 R08: 0000000000000dc0 R09: 000000000000040a R10: 0000000000000000 R11: ffff88807bdd0ae8 R12: 0000000000000000 R13: 0000000000000000 R14: ffff88807bea3100 R15: 0000000000000001 FS: 00007f10db393700(0000) GS:ffff88807dc00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000080 CR3: 000000007bd0f004 CR4: 00000000003706f0 Call Trace: fib_create_info+0x64d/0xaf7 fib_table_insert+0xf6/0x581 ? __vma_adjust+0x3b6/0x4d4 inet_rtm_newroute+0x56/0x70 rtnetlink_rcv_msg+0x1e3/0x20d ? rtnl_calcit.isra.0+0xb8/0xb8 netlink_rcv_skb+0x5b/0xac netlink_unicast+0xfa/0x17b netlink_sendmsg+0x334/0x353 sock_sendmsg_nosec+0xf/0x3f ____sys_sendmsg+0x1a0/0x1fc ? copy_msghdr_from_user+0x4c/0x61 ___sys_sendmsg+0x63/0x84 ? handle_mm_fault+0xa39/0x11b5 ? sockfd_lookup_light+0x72/0x9a __sys_sendmsg+0x50/0x6e do_syscall_64+0x54/0xbe entry_SYSCALL_64_after_hwframe+0x44/0xa9 RIP: 0033:0x7f10dacc0bb7 Code: d8 64 89 02 48 c7 c0 ff ff ff ff eb cd 66 0f 1f 44 00 00 8b 05 9a 4b 2b 00 85 c0 75 2e 48 63 ff 48 63 d2 b8 2e 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 01 c3 48 8b 15 b1 f2 2a 00 f7 d8 64 89 02 48 RSP: 002b:00007ffcbe628bf8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e RAX: ffffffffffffffda RBX: 00007ffcbe628f80 RCX: 00007f10dacc0bb7 RDX: 0000000000000000 RSI: 00007ffcbe628c60 RDI: 0000000000000003 RBP: 000000005f41099c R08: 0000000000000001 R09: 0000000000000008 R10: 00000000000005e9 R11: 0000000000000246 R12: 0000000000000000 R13: 0000000000000000 R14: 00007ffcbe628d70 R15: 0000563a86c6e440 Modules linked in: CR2: 0000000000000080 CC: David Ahern <dsahern@gmail.com> Fixes: 430a0491 ("nexthop: Add support for nexthop groups") Reported-by:<syzbot+a61aa19b0c14c8770bd9@syzkaller.appspotmail.com> Signed-off-by: