On Mon, 23 Mar 2020, Kyungtae Kim wrote: > We report a bug (in linux-5.5.11) found by FuzzUSB (a modified version > of syzkaller) > > In function usb_hcd_unlink_urb (driver/usb/core/hcd.c:1607), it tries to > read "urb->use_count". But it seems the instance "urb" was > already freed (right after urb->dev at line 1597) by the function "urb_destroy" > in a different thread, which caused memory access violation. > To solve, it may need to check if urb is valid before urb->use_count, > to avoid such freed memory access. No, the problem is "free while still in use", caused by the fact that usb_sg_cancel() fails to indicate it is using the data structures. > kernel config: https://kt0755.github.io/etc/config_v5.5.11 > > ================================================================== > BUG: KASAN: use-after-free in atomic_read > include/asm-generic/atomic-instrumented.h:26 [inline] > BUG: KASAN: use-after-free in usb_hcd_unlink_urb+0x5f/0x170 > drivers/usb/core/hcd.c:1607 > Read of size 4 at addr ffff888065379610 by task kworker/u4:1/27 Here is a patch which ought to fix the problem. Can you test it? Alan Stern Index: usb-devel/drivers/usb/core/message.c =================================================================== --- usb-devel.orig/drivers/usb/core/message.c +++ usb-devel/drivers/usb/core/message.c @@ -588,12 +588,13 @@ void usb_sg_cancel(struct usb_sg_request int i, retval; spin_lock_irqsave(&io->lock, flags); - if (io->status) { + if (io->status || io->count == 0) { spin_unlock_irqrestore(&io->lock, flags); return; } /* shut everything down */ io->status = -ECONNRESET; + io->count++; /* Keep the request alive until we're done */ spin_unlock_irqrestore(&io->lock, flags); for (i = io->entries - 1; i >= 0; --i) { @@ -607,6 +608,12 @@ void usb_sg_cancel(struct usb_sg_request dev_warn(&io->dev->dev, "%s, unlink --> %d\n", __func__, retval); } + + spin_lock_irqsave(&io->lock, flags); + io->count--; + if (!io->count) + complete(&io->complete); + spin_unlock_irqrestore(&io->lock, flags); } EXPORT_SYMBOL_GPL(usb_sg_cancel);
