gtp: fix use-after-free and null-ptr-deref in gtp_genl_dump_pdp()

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

gtp: fix use-after-free and null-ptr-deref in gtp_genl_dump_pdp()

The gtp_net_ops pernet operations structure for the subsystem must be

registered before registering the generic netlink family.

Syzkaller hit 'general protection fault in gtp_genl_dump_pdp' bug:

general protection fault, probably for non-canonical address

0xdffffc0000000002: 0000 [#1] PREEMPT SMP KASAN NOPTI

KASAN: null-ptr-deref in range [0x0000000000000010-0x0000000000000017]

CPU: 1 PID: 5826 Comm: gtp Not tainted 6.8.0-rc3-std-def-alt1 #1

Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.0-alt1 04/01/2014

RIP: 0010:gtp_genl_dump_pdp+0x1be/0x800 [gtp]

Code: c6 89 c6 e8 64 e9 86 df 58 45 85 f6 0f 85 4e 04 00 00 e8 c5 ee 86

df 48 8b 54 24 18 48 b8 00 00 00 00 00 fc ff df 48 c1 ea 03 <80>

3c 02 00 0f 85 de 05 00 00 48 8b 44 24 18 4c 8b 30 4c 39 f0 74

RSP: 0018:ffff888014107220 EFLAGS: 00010202

RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000

RDX: 0000000000000002 RSI: 0000000000000000 RDI: 0000000000000000

RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000

R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000

R13: ffff88800fcda588 R14: 0000000000000001 R15: 0000000000000000

FS: 00007f1be4eb05c0(0000) GS:ffff88806ce80000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: 00007f1be4e766cf CR3: 000000000c33e000 CR4: 0000000000750ef0

PKRU: 55555554

Call Trace:

<TASK>

? show_regs+0x90/0xa0

? die_addr+0x50/0xd0

? exc_general_protection+0x148/0x220

? asm_exc_general_protection+0x22/0x30

? gtp_genl_dump_pdp+0x1be/0x800 [gtp]

? __alloc_skb+0x1dd/0x350

? __pfx___alloc_skb+0x10/0x10

genl_dumpit+0x11d/0x230

netlink_dump+0x5b9/0xce0

? lockdep_hardirqs_on_prepare+0x253/0x430

? __pfx_netlink_dump+0x10/0x10

? kasan_save_track+0x10/0x40

? __kasan_kmalloc+0x9b/0xa0

? genl_start+0x675/0x970

__netlink_dump_start+0x6fc/0x9f0

genl_family_rcv_msg_dumpit+0x1bb/0x2d0

? __pfx_genl_family_rcv_msg_dumpit+0x10/0x10

? genl_op_from_small+0x2a/0x440

? cap_capable+0x1d0/0x240

? __pfx_genl_start+0x10/0x10

? __pfx_genl_dumpit+0x10/0x10

? __pfx_genl_done+0x10/0x10

? security_capable+0x9d/0xe0