On Tue Jul 29 13:13:32 2025 +0300, Larshin Sergey wrote:
> Syzbot reports a KASAN issue as below:
> BUG: KASAN: use-after-free in __create_pipe include/linux/usb.h:1945 [inline]
> BUG: KASAN: use-after-free in send_packet+0xa2d/0xbc0
> drivers/media/rc/imon.c:627
> Read of size 4 at addr ffff8880256fb000 by task syz-executor314/4465
>
> CPU: 2 PID: 4465 Comm: syz-executor314 Not tainted 6.0.0-rc1-syzkaller #0
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.14.0-2 04/01/2014
> Call Trace:
> <TASK>
> __dump_stack lib/dump_stack.c:88 [inline]
> dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
> print_address_description mm/kasan/report.c:317 [inline]
> print_report.cold+0x2ba/0x6e9 mm/kasan/report.c:433
> kasan_report+0xb1/0x1e0 mm/kasan/report.c:495
> __create_pipe include/linux/usb.h:1945 [inline]
> send_packet+0xa2d/0xbc0 drivers/media/rc/imon.c:627
> vfd_write+0x2d9/0x550 drivers/media/rc/imon.c:991
> vfs_write+0x2d7/0xdd0 fs/read_write.c:576
> ksys_write+0x127/0x250 fs/read_write.c:631
> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
> entry_SYSCALL_64_after_hwframe+0x63/0xcd
>
> The iMON driver improperly releases the usb_device reference in
> imon_disconnect without coordinating with active users of the
> device.
>
> Specifically, the fields usbdev_intf0 and usbdev_intf1 are not
> protected by the users counter (ictx->users). During probe,
> imon_init_intf0 or imon_init_intf1 increments the usb_device
> reference count depending on the interface. However, during
> disconnect, usb_put_dev is called unconditionally, regardless of
> actual usage.
>
> As a result, if vfd_write or other operations are still in
> progress after disconnect, this can lead to a use-after-free of
> the usb_device pointer.
>
> Thread 1 vfd_write Thread 2 imon_disconnect
> ...
> if
> usb_put_dev(ictx->usbdev_intf0)
> else
> usb_put_dev(ictx->usbdev_intf1)
> ...
> while
> send_packet
> if
> pipe = usb_sndintpipe(
> ictx->usbdev_intf0) UAF
> else
> pipe = usb_sndctrlpipe(
> ictx->usbdev_intf0, 0) UAF
>
> Guard access to usbdev_intf0 and usbdev_intf1 after disconnect by
> checking ictx->disconnected in all writer paths. Add early return
> with -ENODEV in send_packet(), vfd_write(), lcd_write() and
> display_open() if the device is no longer present.
>
> Set and read ictx->disconnected under ictx->lock to ensure memory
> synchronization. Acquire the lock in imon_disconnect() before setting
> the flag to synchronize with any ongoing operations.
>
> Ensure writers exit early and safely after disconnect before the USB
> core proceeds with cleanup.
>
> Found by Linux Verification Center (linuxtesting.org) with Syzkaller.
>
> Reported-by: [email protected]
> Closes: https://syzkaller.appspot.com/bug?extid=f1a69784f6efe748c3bf
> Fixes: 21677cfc562a ("V4L/DVB: ir-core: add imon driver")
> Cc: [email protected]
>
> Signed-off-by: Larshin Sergey <[email protected]>
> Signed-off-by: Sean Young <[email protected]>
> Signed-off-by: Hans Verkuil <[email protected]>
Patch committed.
Thanks,
Hans Verkuil
drivers/media/rc/imon.c | 27 ++++++++++++++++++++-------
1 file changed, 20 insertions(+), 7 deletions(-)
---
diff --git a/drivers/media/rc/imon.c b/drivers/media/rc/imon.c
index 91d05aadced3..35b9e07003d8 100644
--- a/drivers/media/rc/imon.c
+++ b/drivers/media/rc/imon.c
@@ -531,7 +531,9 @@ static int display_open(struct inode *inode, struct file
*file)
mutex_lock(&ictx->lock);
- if (!ictx->display_supported) {
+ if (ictx->disconnected) {
+ retval = -ENODEV;
+ } else if (!ictx->display_supported) {
pr_err("display not supported by device\n");
retval = -ENODEV;
} else if (ictx->display_isopen) {
@@ -595,6 +597,9 @@ static int send_packet(struct imon_context *ictx)
lockdep_assert_held(&ictx->lock);
+ if (ictx->disconnected)
+ return -ENODEV;
+
/* Check if we need to use control or interrupt urb */
if (!ictx->tx_control) {
pipe = usb_sndintpipe(ictx->usbdev_intf0,
@@ -949,12 +954,14 @@ static ssize_t vfd_write(struct file *file, const char
__user *buf,
static const unsigned char vfd_packet6[] = {
0x01, 0x00, 0x00, 0x00, 0x00, 0xFF, 0xFF };
- if (ictx->disconnected)
- return -ENODEV;
-
if (mutex_lock_interruptible(&ictx->lock))
return -ERESTARTSYS;
+ if (ictx->disconnected) {
+ retval = -ENODEV;
+ goto exit;
+ }
+
if (!ictx->dev_present_intf0) {
pr_err_ratelimited("no iMON device present\n");
retval = -ENODEV;
@@ -1029,11 +1036,13 @@ static ssize_t lcd_write(struct file *file, const char
__user *buf,
int retval = 0;
struct imon_context *ictx = file->private_data;
- if (ictx->disconnected)
- return -ENODEV;
-
mutex_lock(&ictx->lock);
+ if (ictx->disconnected) {
+ retval = -ENODEV;
+ goto exit;
+ }
+
if (!ictx->display_supported) {
pr_err_ratelimited("no iMON display present\n");
retval = -ENODEV;
@@ -2507,7 +2516,11 @@ static void imon_disconnect(struct usb_interface
*interface)
int ifnum;
ictx = usb_get_intfdata(interface);
+
+ mutex_lock(&ictx->lock);
ictx->disconnected = true;
+ mutex_unlock(&ictx->lock);
+
dev = ictx->dev;
ifnum = interface->cur_altsetting->desc.bInterfaceNumber;
