Re: [PATCH 1/1] gtp: fix use-after-free and null-ptr-deref in gtp_genl_dump_pdp()

[kovalev@altlinux.org]

Hi,

24.01.2024 14:52, Eric Dumazet wrote:
> On Wed, Jan 24, 2024 at 12:20 PM <kovalev@altlinux.org> wrote:
>> 24.01.2024 13:57, Eric Dumazet wrote:
>>> Oh wait, this is a 5.10 kernel ?
>> Yes, but the bug is reproduced on the latest stable kernels.
>>> Please generate a stack trace using a recent tree, it is possible the
>>> bug has been fixed already.
>> See [PATCH 0/1] above, there's a stack for the 6.6.13 kernel at the
>> bottom of the message.
> Ah, ok. Not sure why you sent a cover letter for a single patch...
>
> Setting a boolean, in a module that can disappear will not prevent the
> module from disappearing.
>
> This work around might work, or might not work, depending on timing,
> preemptions, ....
>
> Thanks.

I tested running the reproducer [1] on the 6.8-rc3 kernel, the crash 
occurs in less than 10 seconds and the qemu VM restarts:

dmesg -w:

[  106.941736] gtp: GTP module unloaded
[  106.962548] gtp: GTP module loaded (pdp ctx size 104 bytes)
[  107.014691] gtp: GTP module unloaded
[  107.041554] gtp: GTP module loaded (pdp ctx size 104 bytes)
[  107.082283] gtp: GTP module unloaded
[  107.123268] general protection fault, probably for non-canonical 
address 0xdffffc0000000002: 0000 [#1] PREEMPT SMP KASAN NOPTI
[  107.124050] KASAN: null-ptr-deref in range 
[0x0000000000000010-0x0000000000000017]
[  107.124339] CPU: 1 PID: 5826 Comm: gtp Not tainted 
6.8.0-rc3-std-def-alt1 #1
[  107.124604] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 
1.16.0-alt1 04/01/2014
[  107.124916] RIP: 0010:gtp_genl_dump_pdp+0x1be/0x800 [gtp]
[  107.125141] 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
[  107.125960] RSP: 0018:ffff888014107220 EFLAGS: 00010202
[  107.126164] RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 
0000000000000000
[  107.126434] RDX: 0000000000000002 RSI: 0000000000000000 RDI: 
0000000000000000
[  107.126707] RBP: 0000000000000000 R08: 0000000000000000 R09: 
0000000000000000
[  107.126976] R10: 0000000000000000 R11: 0000000000000000 R12: 
0000000000000000
[  107.127245] R13: ffff88800fcda588 R14: 0000000000000001 R15: 
0000000000000000
[  107.127515] FS:  00007f1be4eb05c0(0000) GS:ffff88806ce80000(0000) 
knlGS:0000000000000000
[  107.127955] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  107.128177] CR2: 00007f1be4e766cf CR3: 000000000c33e000 CR4: 
0000000000750ef0
[  107.128450] PKRU: 55555554
[  107.128577] Call Trace:
[  107.128699]  <TASK>
[  107.128790]  ? show_regs+0x90/0xa0
[  107.128935]  ? die_addr+0x50/0xd0
[  107.129075]  ? exc_general_protection+0x148/0x220
[  107.129267]  ? asm_exc_general_protection+0x22/0x30
[  107.129469]  ? gtp_genl_dump_pdp+0x1be/0x800 [gtp]
[  107.129677]  ? __alloc_skb+0x1dd/0x350
[  107.129831]  ? __pfx___alloc_skb+0x10/0x10
[  107.129999]  genl_dumpit+0x11d/0x230
[  107.130150]  netlink_dump+0x5b9/0xce0
[  107.130301]  ? lockdep_hardirqs_on_prepare+0x253/0x430
[  107.130503]  ? __pfx_netlink_dump+0x10/0x10
[  107.130686]  ? kasan_save_track+0x10/0x40
[  107.130849]  ? __kasan_kmalloc+0x9b/0xa0
[  107.131009]  ? genl_start+0x675/0x970
[  107.131162]  __netlink_dump_start+0x6fc/0x9f0
[  107.131341]  genl_family_rcv_msg_dumpit+0x1bb/0x2d0
[  107.131538]  ? __pfx_genl_family_rcv_msg_dumpit+0x10/0x10
[  107.131754]  ? genl_op_from_small+0x2a/0x440
[  107.131972]  ? cap_capable+0x1d0/0x240
[  107.132127]  ? __pfx_genl_start+0x10/0x10
[  107.132292]  ? __pfx_genl_dumpit+0x10/0x10
[  107.132461]  ? __pfx_genl_done+0x10/0x10
[  107.132645]  ? security_capable+0x9d/0xe0

With the proposed patch applied, such a crash is not observed during 
long-term testing.

[1] 
https://lore.kernel.org/lkml/20240124101404.161655-1-kovalev@altlinux.org/T/#mf9b411baec52858b1c9118c671f26a6dc424e7b4

-- 
Regards,
Vasiliy Kovalev