[lvc-project] [PATCH] usb: dvb-usb-v2: fix i2c race condition during device probe

Tue Jul 22 14:02:28 MSK 2025

On Tue, 22. Jul 12:22, Nalivayko Sergey wrote:
> syzbot reports a KASAN issue as below:
> 
> Oops: general protection fault, probably for non-canonical address 0xdffffc0000000019: 0000 [#1] SMP KASAN PTI
> KASAN: null-ptr-deref in range [0x00000000000000c8-0x00000000000000cf]
> CPU: 1 UID: 0 PID: 5849 Comm: syz-executor279 Not tainted 6.15.0-rc2-syzkaller #0 PREEMPT(full) 
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
> RIP: 0010:__mutex_lock_common kernel/locking/mutex.c:580 [inline]
> RIP: 0010:__mutex_lock+0x15d/0x10c0 kernel/locking/mutex.c:746
> Code: c0 80 f6 73 9a 48 c1 e8 03 42 0f b6 04 38 84 c0 0f 85 07 0e 00 00 83 3d 40 ba 41 0e 00 75 21 49 8d 7e 60 48 89 f8 48 c1 e8 03 <42> 80 3c 38 00 74 05 e8 17 52 fb f5 4d 39 76 60 0f 85 81 0d 00 00
> RSP: 0018:ffffc90004206f80 EFLAGS: 00010202
> RAX: 0000000000000019 RBX: ffffc90004207040 RCX: ffffffff9a73f603
> RDX: ffff888035f65a00 RSI: ffffffff8e4fde18 RDI: 00000000000000c8
> RBP: ffffc90004207118 R08: ffffc90004207087 R09: 0000000000000000
> R10: ffffc90004207060 R11: fffff52000840e11 R12: 0000000000000000
> R13: ffffc90004207048 R14: 0000000000000068 R15: dffffc0000000000
> FS:  0000555594939380(0000) GS:ffff888125093000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f79554c50f0 CR3: 000000007cfd2000 CR4: 00000000003526f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400

Содержимое регистров и строчка с 'Code:' длиной 202 символа не вносит
никакой полезной информации для читателя. Лучше убрать, чтобы не
захламлять текст коммита.

> Call Trace:
>  <TASK>
>  dvb_usbv2_generic_write+0x26/0x50 drivers/media/usb/dvb-usb-v2/dvb_usb_urb.c:77
>  mxl111sf_ctrl_msg+0x172/0x2e0 drivers/media/usb/dvb-usb-v2/mxl111sf.c:73
>  mxl111sf_write_reg+0xda/0x1f0 drivers/media/usb/dvb-usb-v2/mxl111sf.c:123
>  mxl111sf_i2c_start drivers/media/usb/dvb-usb-v2/mxl111sf-i2c.c:130 [inline]
>  mxl111sf_i2c_sw_xfer_msg drivers/media/usb/dvb-usb-v2/mxl111sf-i2c.c:-1 [inline]
>  mxl111sf_i2c_xfer+0x923/0x8aa0 drivers/media/usb/dvb-usb-v2/mxl111sf-i2c.c:813
>  __i2c_transfer+0x859/0x2250 drivers/i2c/i2c-core-base.c:-1
>  i2c_transfer+0x2c2/0x430 drivers/i2c/i2c-core-base.c:2315
>  i2c_transfer_buffer_flags+0x182/0x260 drivers/i2c/i2c-core-base.c:2343
>  i2c_master_recv include/linux/i2c.h:79 [inline]
>  i2cdev_read+0x10a/0x220 drivers/i2c/i2c-dev.c:155
>  vfs_read+0x21f/0xb90 fs/read_write.c:568
>  ksys_read+0x19d/0x2d0 fs/read_write.c:713
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0xf3/0x230 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f795544e4e9
> Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 c1 17 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007ffc002847a8 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
> RAX: ffffffffffffffda RBX: 0000200000000000 RCX: 00007f795544e4e9
> RDX: 0000000000000063 RSI: 0000000000000000 RDI: 0000000000000004
> RBP: 00000000000f4240 R08: 00232d6332692f76 R09: 00000000000000a0
> R10: 000000000000000f R11: 0000000000000246 R12: 0000000000000001
> R13: 00007ffc002849c8 R14: 00007ffc002847d0 R15: 00007ffc002847c0

Аналогично.

>  </TASK>
> 
> The current implementation of dvb-usb-v2 initializes i2c device in 
> dvb_usbv2_probe() while making it immediately available for data transfers. 
> This creates a window where userspace can trigger dvb_usbv2_generic_write 
> operations before device initialization completes, potentially leading to 
> NULL pointer dereference and kernel panic.
> 
> 
>       Thread 1 (probe device)             Thread 2 (receive i2c data)
>     ...
>     dvb_usbv2_probe()
>       ...
>       d->priv = kzalloc(
>           d->props->size_of_priv, 
>           GFP_KERNEL);
>       ...
>       dvb_usbv2_init()
>       ...
>         // can read data from i2c 
>         dvb_usbv2_i2c_init()
>       ...
>                                         ...
>                                         i2cdev_read()
>                                         ...
>                                           // d->priv data is invalid. UB
>                                           mxl111sf_i2c_xfer()
>                                             ...
>                                             mxl111sf_ctrl_msg()
>                                               ...
>                                               // null ptr deref
>                                               dvb_usbv2_generic_write()
>                                         ...
>       ...
>       // d->priv data is valid
>       dvb_usbv2_adapter_init()
>       ...
> 
> Acquire i2c mutex in probe function to prevent data access before device 
> completes initialization, thus avoiding invalid memory access.

Некоторые драйверы могут захватывать этот мьютекс в процессе исполнения
probe-рутины, что приведёт к дедлоку. Например,

dvb_usbv2_probe()
  mutex_lock()
  dvb_usbv2_init()
    dvb_usbv2_adapter_init()
      dvb_usbv2_adapter_dvb_init()
        ->read_mac_address()
          pctv452e_read_mac_address()
            mutex_lock()   <- ещё раз

Месиво здесь конечно в dvb-usb, мне пока кроме флага-состояния ничего на
ум не приходит.

> 
> Reported-by: syzbot+f9f5333782a854509322 at syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=f9f5333782a854509322
> Fixes: dd0f5e0b7554 ("[media] dvb_usb_v2: get rid of deferred probe")
> Cc: stable at vger.kernel.org
> Signed-off-by: Nalivayko Sergey <Sergey.Nalivayko at kaspersky.com>
> ---
>  drivers/media/usb/dvb-usb-v2/dvb_usb_core.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/media/usb/dvb-usb-v2/dvb_usb_core.c b/drivers/media/usb/dvb-usb-v2/dvb_usb_core.c
> index f1c79f351ec8..aa414735fe7d 100644
> --- a/drivers/media/usb/dvb-usb-v2/dvb_usb_core.c
> +++ b/drivers/media/usb/dvb-usb-v2/dvb_usb_core.c
> @@ -917,15 +917,16 @@ int dvb_usbv2_probe(struct usb_interface *intf,
>  	d->udev = udev;
>  	d->props = driver_info->props;
>  
> +	mutex_init(&d->usb_mutex);
> +	mutex_init(&d->i2c_mutex);
> +	mutex_lock(&d->i2c_mutex);
> +
>  	if (intf->cur_altsetting->desc.bInterfaceNumber !=
>  			d->props->bInterfaceNumber) {
>  		ret = -ENODEV;
>  		goto err_kfree_d;
>  	}
>  
> -	mutex_init(&d->usb_mutex);
> -	mutex_init(&d->i2c_mutex);
> -
>  	if (d->props->size_of_priv) {
>  		d->priv = kzalloc(d->props->size_of_priv, GFP_KERNEL);
>  		if (!d->priv) {
> @@ -987,6 +988,7 @@ int dvb_usbv2_probe(struct usb_interface *intf,
>  			KBUILD_MODNAME, d->name);
>  exit:
>  	usb_set_intfdata(intf, d);
> +	mutex_unlock(&d->i2c_mutex);
>  
>  	return 0;
>  err_free_all:
> @@ -996,6 +998,7 @@ int dvb_usbv2_probe(struct usb_interface *intf,
>  err_kfree_priv:
>  	kfree(d->priv);
>  err_kfree_d:
> +	mutex_unlock(&d->i2c_mutex);
>  	kfree(d);
>  err:
>  	dev_dbg(&udev->dev, "%s: failed=%d\n", __func__, ret);
> -- 
> 2.30.2