Date: Wed, 24 Apr 2024 07:36:57 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Yuxuan Hu <20373622@...a.edu.cn>, gregkh@...uxfoundation.org,
 johan@...nel.org, davem@...emloft.net, u.kleine-koenig@...gutronix.de,
 Jonathan.Cameron@...wei.com, francesco.dolcini@...adex.com,
 jirislaby@...nel.org
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
 baijiaju1990@...il.com, sy2239101@...a.edu.cn,
 Yuxuan Hu <yuxuanhu@...a.edu.cn>
Subject: Re: [PATCH] nfc: pn533: Fix null-ptr-deref in pn533_recv_frame()

On 22/04/2024 10:04, Yuxuan Hu wrote:
> From: Yuxuan Hu <yuxuanhu@...a.edu.cn>
> 
> Our fuzzing tool found a null-ptr-deref in function pn533_recv_frame 
> (/drivers/nfc/pn533/pn533.c) in kernel 6.8.
> 
> (1.1) When execute the NFC_CMD_START_POLL command via netlink, the 
> pn533_send_cmd_async function (/drivers/nfc/pn533/pn533.c: 1714) is 
> called, which sends the PN533_CMD_IN_AUTOPOLL command packet.
> 
> (2.1) If a pn533 response frame that does not match the command is 
> received, the following call sequence is executed:
> pn533_recv_frame (/drivers/nfc/pn533/pn533.c: 2165)
>     pn533_rx_frame_is_cmd_response (/drivers/nfc/pn533/pn533.c: 2194)
>     pn533_wq_cmd_complete (/drivers/nfc/pn533/pn533.c: 2022)
>         pn533_send_async_complete (/drivers/nfc/pn533/pn533.c: 547)
>             pn533_autopoll_complete (/drivers/nfc/pn533/pn533.c: 414)
> 
> (2.2) After completing (2.1), dev->cmd is freed and set to null 
> (/drivers/nfc/pn533/pn533.c: 432-433).
> 
> (3.1) If another incorrect pn533 response frame is received during 
> the above process, (2.1) and (2.2) will be executed concurrently, and 
> the initial process setting dev->cmd to null causes the concurrent 
> process to trigger a null-ptr-deref in pn533_recv_frame.
> 
> Although pn533_recv_frame checks for dev->cmd at the beginning, it is 
> possible that dev->cmd is set to null after the check.

That sounds reasonable... but solution does not.

> 
> Through our verification, this concurrent vulnerability has a high 
> probability of occurrence and needs to be fixed.
> 
> Kernel print messages when null-ptr-deref is triggered (including PN533 
> packets, PN533 module errors, and KASAN reports) are as follows.
> We added printk of the data packets, and printk before the relevant steps 
> in pn533_send_async_complete and pn533_recv_frame.
> 
>   -> 00 00 FF 08 F8 D4 60 FF 03 00 11 12 04 A3 00 
>   <- 00 00 FF 00 FF 00 
>   <- 00 00 FF 0E F2 D5 86 01 10 09 01 00 20 08 04 9B 2C EE 9F 0A 00 
>   tty tty60: NFC: It it not the response to the last command
>   arted polling nfc device
>   <- 00 00 FF 03 FD D5 41 00 EA 00 
>   tty tty60: NFC: pn533_autopoll_complete  autopoll complete error -5
>   tty tty60: NFC: It it not the response to the last command
>   tty tty60: NFC: Error -5 when running autopoll
>   tty tty60: NFC: autopoll operation has been stopped
>   pn533_send_async_complete: set dev->cmd to null!!!
>   pn533_recv_frame: dev->cmd is null!!!
>   BUG: kernel NULL pointer dereference, address: 0000000000000014
>   #PF: supervisor write access in kernel mode
>   #PF: error_code(0x0002) - not-present page
>   PGD 0 P4D 0 
>   Oops: 0002 [#1] PREEMPT SMP KASAN PTI
>   CPU: 0 PID: 5541 Comm: kworker/0:0 Tainted: G           O       6.8.0 #1
>   Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014
>   Workqueue: events nfcvirt_recv_work [nfcvirt]
>   RIP: 0010:pn533_recv_frame+0x18a/0x1e0 [pn533]
>   Code: 43 ff ff ff 48 8b bb 80 02 00 00 48 c7 c6 0b 02 46 c0 31 c0 e8 97 64 4f c4 48 83 bb b0 01 00 00 00 74 3f 48 8b 83 b0 01 00 00 <c7> 40 14 fb ff ff ff 48 8b 83 b0 01 00 00 48 85 c0 0f 85 3b ff ff
>   RSP: 0018:ffff88802665fc68 EFLAGS: 00010246
>   RAX: 0000000000000000 RBX: ffff88804a13b800 RCX: ad381de3b3cd5e00
>   RDX: 1ffff11004ccbf38 RSI: 0000000000000008 RDI: ffff88802665f9e0
>   RBP: ffff88804fb25000 R08: ffff88802665f9e7 R09: 1ffff11004ccbf3c
>   R10: dffffc0000000000 R11: ffffed1004ccbf3d R12: 0000000000001950
>   R13: ffff88804ab80000 R14: ffff888021d22640 R15: ffff88802665fcb0
>   FS:  0000000000000000(0000) GS:ffff88806d200000(0000) knlGS:0000000000000000
>   CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>   CR2: 0000000000000014 CR3: 0000000004ebc000 CR4: 00000000000006f0

Please trim the log from irrelevant register dumps.

>   Call Trace:
>    <TASK>
>    ? __die_body+0x62/0xb0
>    ? page_fault_oops+0x421/0x740
>    ? kernelmode_fixup_or_oops+0x1d0/0x1d0
>    ? asan.module_ctor+0x10/0x10
>    ? vprintk_emit+0x3f0/0x3f0
>    ? kernelmode_fixup_or_oops+0x163/0x1d0
>    ? do_user_addr_fault+0xb6c/0xde0
>    ? irq_work_queue+0x54/0xa0
>    ? do_kern_addr_fault+0x160/0x160
>    ? __call_rcu_common+0x518/0xc30
>    ? _dev_err+0x106/0x150
>    ? exc_page_fault+0x66/0x1a0
>    ? asm_exc_page_fault+0x22/0x30
>    ? pn533_recv_frame+0x18a/0x1e0 [pn533]
>    ? pn533_recv_frame+0x1d7/0x1e0 [pn533]
>    nfcvirt_recv_work+0x24e/0x320 [nfcvirt]
>    ? wake_bit_function+0x230/0x230
>    process_one_work+0x4f0/0xab0
>    worker_thread+0x8af/0xee0
>    ? process_one_work+0xab0/0xab0
>    kthread+0x275/0x300
>    ? process_one_work+0xab0/0xab0
>    ? kthread_blkcg+0xa0/0xa0
>    ret_from_fork+0x30/0x60
>    ? kthread_blkcg+0xa0/0xa0
>    ret_from_fork_asm+0x11/0x20
>    </TASK>
>   Modules linked in: nfcvirt(O) pn533(O) nfc(O) ki_coverage(O) [last unloaded: pn533(O)]
>   CR2: 0000000000000014
>   ---[ end trace 0000000000000000 ]---
>   RIP: 0010:pn533_recv_frame+0x18a/0x1e0 [pn533]
>   Code: 43 ff ff ff 48 8b bb 80 02 00 00 48 c7 c6 0b 02 46 c0 31 c0 e8 97 64 4f c4 48 83 bb b0 01 00 00 00 74 3f 48 8b 83 b0 01 00 00 <c7> 40 14 fb ff ff ff 48 8b 83 b0 01 00 00 48 85 c0 0f 85 3b ff ff
>   RSP: 0018:ffff88802665fc68 EFLAGS: 00010246
>   RAX: 0000000000000000 RBX: ffff88804a13b800 RCX: ad381de3b3cd5e00
>   RDX: 1ffff11004ccbf38 RSI: 0000000000000008 RDI: ffff88802665f9e0
>   RBP: ffff88804fb25000 R08: ffff88802665f9e7 R09: 1ffff11004ccbf3c
>   R10: dffffc0000000000 R11: ffffed1004ccbf3d R12: 0000000000001950
>   R13: ffff88804ab80000 R14: ffff888021d22640 R15: ffff88802665fcb0
>   FS:  0000000000000000(0000) GS:ffff88806d200000(0000) knlGS:0000000000000000
>   CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>   CR2: 0000000000000014 CR3: 0000000004ebc000 CR4: 00000000000006f0

Same here.

This just makes the commit log less readable.

> 
> Signed-off-by: Yuxuan Hu <yuxuanhu@...a.edu.cn>
> ---
>  drivers/nfc/pn533/pn533.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/nfc/pn533/pn533.c b/drivers/nfc/pn533/pn533.c
> index b19c39dcfbd9..a80a23332f59 100644
> --- a/drivers/nfc/pn533/pn533.c
> +++ b/drivers/nfc/pn533/pn533.c
> @@ -2190,9 +2190,13 @@ void pn533_recv_frame(struct pn533 *dev, struct sk_buff *skb, int status)
>  
>  	if (!dev->ops->rx_is_frame_valid(skb->data, dev)) {
>  		nfc_err(dev->dev, "Received an invalid frame\n");

Imagine here dev->cmd != NULL...

> +		if (!dev->cmd)
> +			goto sched_wq;

.. but here is being NULL-ified by pn533_send_async_complete(). How
does your solution prevent anything? I assume pn533_recv_frame() will be
executed in parallel to the workqueue.

A bit better solution would be to NULL-ify dev->cmd at the beginning of
pn533_send_async_complete(), because that seems logical. The complete
callback takes ownership of dev->cmd, so why it performs the assignment
at the end?

However even above code will keep the race open for short period.
Probably some locking would solve it or checking for dev->cmd in few
places with barriers.

Best regards,
Krzysztof

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