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

[Eric Dumazet <edumazet@google.com>]

On Fri, Feb 9, 2024 at 7:16 PM <kovalev@altlinux.org> wrote:
>
> 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.

Maybe, but the patch is not good, I think I and Pablo gave feedback on this ?

Please trace __netlink_dump_start() content of control->module

gtp_genl_family.module should be set, and we should get it.

Otherwise, if the bug is in the core, we would need a dozen of 'work
arounds because it is better than nothing'

Thank you.