Re: WARNING in wdm_write/usb_submit_urb

[Oliver Neukum <oneukum@suse.com>]

Am Montag, den 19.08.2019, 17:50 -0700 schrieb syzbot:
> syzbot has found a reproducer for the following crash on:

Hi Bjørn,

taking you into CC as you are affected.
V4: <argh>

> HEAD commit:    e06ce4da 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=14a8c0b6600000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=d0c62209eedfd54e
> dashboard link: https://syzkaller.appspot.com/bug?extid=d232cca6ec42c2edb3fc
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12b6dfba600000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15f63a4c600000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+d232cca6ec42c2edb3fc@syzkaller.appspotmail.com
> 
> ------------[ cut here ]------------
> URB 000000005fab893a submitted while active
> WARNING: CPU: 1 PID: 1788 at drivers/usb/core/urb.c:362  
> usb_submit_urb+0x10c1/0x13b0 drivers/usb/core/urb.c:362
> Kernel panic - not syncing: panic_on_warn set ...
> CPU: 1 PID: 1788 Comm: syz-executor522 Not tainted 5.3.0-rc5+ #27
> 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
>   panic+0x2a3/0x6da kernel/panic.c:219
>   __warn.cold+0x20/0x4a kernel/panic.c:576
>   report_bug+0x262/0x2a0 lib/bug.c:186
>   fixup_bug arch/x86/kernel/traps.c:179 [inline]
>   fixup_bug arch/x86/kernel/traps.c:174 [inline]
>   do_error_trap+0x12b/0x1e0 arch/x86/kernel/traps.c:272
>   do_invalid_op+0x32/0x40 arch/x86/kernel/traps.c:291
>   invalid_op+0x23/0x30 arch/x86/entry/entry_64.S:1028
> RIP: 0010:usb_submit_urb+0x10c1/0x13b0 drivers/usb/core/urb.c:362
> Code: 89 de e8 82 bc ef fd 84 db 0f 85 42 f6 ff ff e8 45 bb ef fd 4c 89 fe  
> 48 c7 c7 80 68 18 86 c6 05 27 30 3a 04 01 e8 34 a1 c5 fd <0f> 0b e9 20 f6  
> ff ff c7 44 24 14 01 00 00 00 e9 d7 f6 ff ff 41 bd
> RSP: 0018:ffff8881d036fc98 EFLAGS: 00010286
> RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
> RDX: 0000000000000000 RSI: ffffffff81288cfd RDI: ffffed103a06df85
> RBP: ffff8881cfce56a0 R08: ffff8881d1ce4800 R09: ffffed103b663ee7
> R10: ffffed103b663ee6 R11: ffff8881db31f737 R12: 1ffff1103a06dfa7
> R13: 00000000fffffff0 R14: ffff8881cfce5688 R15: ffff8881d8106d00
>   wdm_write+0x828/0xd87 drivers/usb/class/cdc-wdm.c:423
>   __vfs_write+0x76/0x100 fs/read_write.c:494
>   vfs_write+0x262/0x5c0 fs/read_write.c:558
>   ksys_write+0x127/0x250 fs/read_write.c:611
>   do_syscall_64+0xb7/0x580 arch/x86/entry/common.c:296
>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x447029
> Code: e8 ec e7 ff ff 48 83 c4 18 c3 0f 1f 80 00 00 00 00 48 89 f8 48 89 f7  
> 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff  
> ff 0f 83 3b 07 fc ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007f1e9e0a4da8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
> RAX: ffffffffffffffda RBX: 00000000006dcc28 RCX: 0000000000447029
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000004
> RBP: 00000000006dcc20 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dcc2c
> R13: 0000000020000000 R14: 00000000004af170 R15: 00000000000003e8

#syz test: https://github.com/google/kasan.git e06ce4da

From 8973b1216f931f4c7b82b02186caee9dcae16d24 Mon Sep 17 00:00:00 2001
From: Oliver Neukum <oneukum@suse.com>
Date: Tue, 20 Aug 2019 12:08:19 +0200
Subject: [PATCH] USB: cdc-wdm: fix race between write and disconnect due to
 flag abuse

In case of a disconnect an ongoing flush() has to be made fail.
Nevertheless we cannot be sure that any pending URB has already
finished, so although they will never succeed, they still must
not be touched.
The clean solution for this is to check for WDM_IN_USE
and WDM_DISCONNECTED in flush(). There is no point in ever
clearing WDM_IN_USE, as no further writes make sense.

The issue is as old as the driver.

Fixes: afba937e540c9 ("USB: CDC WDM driver")
Reported-by: syzbot+d232cca6ec42c2edb3fc@syzkaller.appspotmail.com
Signed-off-by: Oliver Neukum <oneukum@suse.com>
---
 drivers/usb/class/cdc-wdm.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/drivers/usb/class/cdc-wdm.c b/drivers/usb/class/cdc-wdm.c
index 1656f5155ab8..f9f7c8a5e091 100644
--- a/drivers/usb/class/cdc-wdm.c
+++ b/drivers/usb/class/cdc-wdm.c
@@ -588,10 +588,20 @@ static int wdm_flush(struct file *file, fl_owner_t id)
 {
 	struct wdm_device *desc = file->private_data;
 
-	wait_event(desc->wait, !test_bit(WDM_IN_USE, &desc->flags));
+	wait_event(desc->wait,
+			/*
+			 * needs both flags. We cannot do with one
+			 * because resetting it would cause a race
+			 * with write() yet we need to signal
+			 * a disconnect
+			 */
+			!test_bit(WDM_IN_USE, &desc->flags) ||
+			test_bit(WDM_DISCONNECTING, &desc->flags));
 
 	/* cannot dereference desc->intf if WDM_DISCONNECTING */
-	if (desc->werr < 0 && !test_bit(WDM_DISCONNECTING, &desc->flags))
+	if (test_bit(WDM_DISCONNECTING, &desc->flags))
+		return -ENODEV;
+	if (desc->werr < 0)
 		dev_err(&desc->intf->dev, "Error in flush path: %d\n",
 			desc->werr);
 
@@ -975,8 +985,6 @@ static void wdm_disconnect(struct usb_interface *intf)
 	spin_lock_irqsave(&desc->iuspin, flags);
 	set_bit(WDM_DISCONNECTING, &desc->flags);
 	set_bit(WDM_READ, &desc->flags);
-	/* to terminate pending flushes */
-	clear_bit(WDM_IN_USE, &desc->flags);
 	spin_unlock_irqrestore(&desc->iuspin, flags);
 	wake_up_all(&desc->wait);
 	mutex_lock(&desc->rlock);
-- 
2.16.4