The syzbot fuzzer found a race between uevent callbacks and gadget driver unregistration that can cause a use-after-free bug: --------------------------------------------------------------- BUG: KASAN: use-after-free in usb_udc_uevent+0x11f/0x130 drivers/usb/gadget/udc/core.c:1732 Read of size 8 at addr ffff888078ce2050 by task udevd/2968 CPU: 1 PID: 2968 Comm: udevd Not tainted 5.19.0-rc4-next-20220628-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/29/2022 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/0x719 mm/kasan/report.c:433 kasan_report+0xbe/0x1f0 mm/kasan/report.c:495 usb_udc_uevent+0x11f/0x130 drivers/usb/gadget/udc/core.c:1732 dev_uevent+0x290/0x770 drivers/base/core.c:2424 --------------------------------------------------------------- The bug occurs because usb_udc_uevent() dereferences udc->driver but does so without acquiring the udc_lock mutex, which protects this field. If the gadget driver is unbound from the udc concurrently with uevent processing, the driver structure may be accessed after it has been deallocated. To prevent the race, we make sure that the routine holds the mutex around the racing accesses. Signed-off-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> Reported-and-tested-by: syzbot+b0de012ceb1e2a97891b@xxxxxxxxxxxxxxxxxxxxxxxxx CC: stable@xxxxxxxxxxxxxxx Link: <https://lore.kernel.org/all/0000000000004de90405a719c951@xxxxxxxxxx> --- As far as I can tell, this bug has always been present. However, the udc_lock mutex used by the patch was added in commit fc274c1e9973 ("USB: gadget: Add a new bus for gadgets"), so this patch won't apply to trees which don't include that commit or a backport of it. I don't know what tag, if any, can express this requirement. [as1983] drivers/usb/gadget/udc/core.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) Index: usb-devel/drivers/usb/gadget/udc/core.c =================================================================== --- usb-devel.orig/drivers/usb/gadget/udc/core.c +++ usb-devel/drivers/usb/gadget/udc/core.c @@ -1728,13 +1728,14 @@ static int usb_udc_uevent(struct device return ret; } - if (udc->driver) { + mutex_lock(&udc_lock); + if (udc->driver) ret = add_uevent_var(env, "USB_UDC_DRIVER=%s", udc->driver->function); - if (ret) { - dev_err(dev, "failed to add uevent USB_UDC_DRIVER\n"); - return ret; - } + mutex_unlock(&udc_lock); + if (ret) { + dev_err(dev, "failed to add uevent USB_UDC_DRIVER\n"); + return ret; } return 0;
