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SubjectRe: KASAN: use-after-free Read in usb_kill_urb
On Fri, 9 Aug 2019, syzbot wrote:

> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit: e96407b4 usb-fuzzer: main usb gadget fuzzer driver
> git tree: https://github.com/google/kasan.git usb-fuzzer
> console output: https://syzkaller.appspot.com/x/log.txt?x=1799392c600000
> kernel config: https://syzkaller.appspot.com/x/.config?x=cfa2c18fb6a8068e
> dashboard link: https://syzkaller.appspot.com/bug?extid=22ae4e3b9fcc8a5c153a
> compiler: gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1134c802600000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13278c4a600000
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+22ae4e3b9fcc8a5c153a@syzkaller.appspotmail.com
>
> ==================================================================
> BUG: KASAN: use-after-free in atomic_read
> include/asm-generic/atomic-instrumented.h:26 [inline]
> BUG: KASAN: use-after-free in usb_kill_urb drivers/usb/core/urb.c:695
> [inline]
> BUG: KASAN: use-after-free in usb_kill_urb+0x24b/0x2c0
> drivers/usb/core/urb.c:687
> Read of size 4 at addr ffff8881d635b110 by task syz-executor672/1999
>
> CPU: 1 PID: 1999 Comm: syz-executor672 Not tainted 5.3.0-rc2+ #25
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Call Trace:
> __dump_stack lib/dump_stack.c:77 [inline]
> dump_stack+0xca/0x13e lib/dump_stack.c:113
> print_address_description+0x6a/0x32c mm/kasan/report.c:351
> __kasan_report.cold+0x1a/0x33 mm/kasan/report.c:482
> kasan_report+0xe/0x12 mm/kasan/common.c:612
> check_memory_region_inline mm/kasan/generic.c:185 [inline]
> check_memory_region+0x128/0x190 mm/kasan/generic.c:192
> atomic_read include/asm-generic/atomic-instrumented.h:26 [inline]
> usb_kill_urb drivers/usb/core/urb.c:695 [inline]
> usb_kill_urb+0x24b/0x2c0 drivers/usb/core/urb.c:687
> ld_usb_abort_transfers+0xb7/0x1d0 drivers/usb/misc/ldusb.c:196
> ld_usb_release+0x19f/0x400 drivers/usb/misc/ldusb.c:406

Since this also involves ldusb.c, maybe it will be fixed by the same
patch as the other bug.

Alan Stern


#syz test: https://github.com/google/kasan.git e96407b4

Index: usb-devel/drivers/usb/core/file.c
===================================================================
--- usb-devel.orig/drivers/usb/core/file.c
+++ usb-devel/drivers/usb/core/file.c
@@ -193,9 +193,10 @@ int usb_register_dev(struct usb_interfac
intf->minor = minor;
break;
}
- up_write(&minor_rwsem);
- if (intf->minor < 0)
+ if (intf->minor < 0) {
+ up_write(&minor_rwsem);
return -EXFULL;
+ }

/* create a usb class device for this usb interface */
snprintf(name, sizeof(name), class_driver->name, minor - minor_base);
@@ -203,12 +204,11 @@ int usb_register_dev(struct usb_interfac
MKDEV(USB_MAJOR, minor), class_driver,
"%s", kbasename(name));
if (IS_ERR(intf->usb_dev)) {
- down_write(&minor_rwsem);
usb_minors[minor] = NULL;
intf->minor = -1;
- up_write(&minor_rwsem);
retval = PTR_ERR(intf->usb_dev);
}
+ up_write(&minor_rwsem);
return retval;
}
EXPORT_SYMBOL_GPL(usb_register_dev);
@@ -234,12 +234,12 @@ void usb_deregister_dev(struct usb_inter
return;

dev_dbg(&intf->dev, "removing %d minor\n", intf->minor);
+ device_destroy(usb_class->class, MKDEV(USB_MAJOR, intf->minor));

down_write(&minor_rwsem);
usb_minors[intf->minor] = NULL;
up_write(&minor_rwsem);

- device_destroy(usb_class->class, MKDEV(USB_MAJOR, intf->minor));
intf->usb_dev = NULL;
intf->minor = -1;
destroy_usb_class();
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