linux-kernel - [PATCH 2/2] media: mxl111sf: fix i2c race condition during device probe

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Message-ID: <20251107154426.2116743-3-Sergey.Nalivayko@kaspersky.com>
Date: Fri, 7 Nov 2025 18:44:26 +0300
From: Nalivayko Sergey <Sergey.Nalivayko@...persky.com>
To: <linux-media@...r.kernel.org>
CC: Nalivayko Sergey <Sergey.Nalivayko@...persky.com>,
	<linux-kernel@...r.kernel.org>, <lvc-project@...uxtesting.org>, Mauro
 Carvalho Chehab <mchehab@...nel.org>, Michael Krufky <mkrufky@...uxtv.org>,
	<syzbot+f9f5333782a854509322@...kaller.appspotmail.com>,
	<stable@...r.kernel.org>
Subject: [PATCH 2/2] media: mxl111sf: fix i2c race condition during device probe

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
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
 </TASK>

This occurs due to a race condition during DVB-USB-V2 device initialization.
While initialization is in progress, I2C data may be read from userspace,
leading to a NULL pointer dereference in dvb_usbv2_generic_write
and a 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()
      ...

Add init_ready flag check to prevent I/O on uninitialized DVB-USB-V2 device.

Reported-by: syzbot+f9f5333782a854509322@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=f9f5333782a854509322
Fixes: 4c66c9205c07 ("[media] dvb-usb: add ATSC support for the Hauppauge WinTV-Aero-M")
Cc: stable@...r.kernel.org
Signed-off-by: Nalivayko Sergey <Sergey.Nalivayko@...persky.com>
---
 drivers/media/usb/dvb-usb-v2/mxl111sf-i2c.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/media/usb/dvb-usb-v2/mxl111sf-i2c.c b/drivers/media/usb/dvb-usb-v2/mxl111sf-i2c.c
index 100a1052dcbc..b7bad90b16dc 100644
--- a/drivers/media/usb/dvb-usb-v2/mxl111sf-i2c.c
+++ b/drivers/media/usb/dvb-usb-v2/mxl111sf-i2c.c
@@ -804,7 +804,7 @@ int mxl111sf_i2c_xfer(struct i2c_adapter *adap,
 	int hwi2c = (state->chip_rev > MXL111SF_V6);
 	int i, ret;
 
-	if (mutex_lock_interruptible(&d->i2c_mutex) < 0)
+	if (!atomic_read(&d->init_ready) || mutex_lock_interruptible(&d->i2c_mutex) < 0)
 		return -EAGAIN;
 
 	for (i = 0; i < num; i++) {
-- 
2.39.5