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SubjectRe: general protection fault in __dev_printk
On Thu, 18 Apr 2019, syzbot wrote:

> syzbot has found a reproducer for the following crash on:
>
> HEAD commit: d34f9519 usb-fuzzer: main usb gadget fuzzer driver
> git tree: https://github.com/google/kasan/tree/usb-fuzzer
> console output: https://syzkaller.appspot.com/x/log.txt?x=10adfe6b200000
> kernel config: https://syzkaller.appspot.com/x/.config?x=c73d1bb5aeaeae20
> dashboard link: https://syzkaller.appspot.com/bug?extid=2eb9121678bdb36e6d57
> compiler: gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=145cb7e3200000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=17f8bd2d200000
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+2eb9121678bdb36e6d57@syzkaller.appspotmail.com
>
> yurex 1-1:0.150: yurex_interrupt - unknown status received: -71
> usb 1-1: USB disconnect, device number 112
> yurex 1-1:0.150: yurex_interrupt - unknown status received: -71
> kasan: CONFIG_KASAN_INLINE enabled
> kasan: GPF could be caused by NULL-ptr deref or user memory access
> general protection fault: 0000 [#1] SMP KASAN PTI
> CPU: 1 PID: 5402 Comm: udevd Not tainted 5.1.0-rc5-319617-gd34f951 #4
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> RIP: 0010:dev_name include/linux/device.h:1087 [inline]
> RIP: 0010:__dev_printk+0x3f/0x215 drivers/base/core.c:3208
> Code: 89 f5 53 e8 1e 24 1c fc 48 85 ed 0f 84 c9 01 00 00 e8 10 24 1c fc 48
> 8d 7d 50 b8 ff ff 37 00 48 89 fa 48 c1 e0 2a 48 c1 ea 03 <80> 3c 02 00 74
> 05 e8 31 39 53 fc 4c 8b 7d 50 4d 85 ff 75 28 e8 e3
> RSP: 0018:ffff8880ad107930 EFLAGS: 00010002
> RAX: dffffc0000000000 RBX: ffffed1015a20f2d RCX: 00000000ffffffed
> RDX: 0000000000000010 RSI: ffffffff85559bf0 RDI: 0000000000000080
> RBP: 0000000000000030 R08: ffff888091578000 R09: ffffed1015a24fc9
> R10: ffffed1015a24fc8 R11: ffff8880ad127e47 R12: ffffffff8f031a00
> R13: ffff8880ad107988 R14: 0000000000000000 R15: ffff88809b9b1600
> FS: 00007fcff04907a0(0000) GS:ffff8880ad100000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007fcff0496000 CR3: 0000000097678000 CR4: 00000000001406e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
> <IRQ>
> _dev_err+0xdc/0x10e drivers/base/core.c:3251
> yurex_interrupt.cold+0x12e/0x13d drivers/usb/misc/yurex.c:183

The problem is that the device can be unregistered before the interrupt
URB is killed. I don't know if the patch below is the right way to fix
this, but it ought to do the job.

Alan Stern


#syz test: https://github.com/google/kasan.git usb-fuzzer

--- a/drivers/usb/misc/yurex.c
+++ b/drivers/usb/misc/yurex.c
@@ -314,6 +314,7 @@ static void yurex_disconnect(struct usb_
usb_deregister_dev(interface, &yurex_class);

/* prevent more I/O from starting */
+ usb_poison_urb(dev->urb);
mutex_lock(&dev->io_mutex);
dev->interface = NULL;
mutex_unlock(&dev->io_mutex);
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