gadgetfs regression (NULL ptr deref) since v4.4-rc7

[Vegard Nossum]

Hi,

Using gadgetfs on latest mainline, I get the following NULL pointer 
dereference:

BUG: unable to handle kernel NULL pointer dereference at           (null)
IP: [<ffffffff81138e89>] __list_del_entry+0x29/0xc0
PGD 34f067 PUD 355067 PMD 0
Oops: 0000 [#1] DEBUG_PAGEALLOC
CPU: 0 PID: 35 Comm: afl-fuzz Not tainted 4.5.0-rc2 #1
task: ffff8800002b1ec0 ti: ffff88000033c000 task.ti: ffff88000033c000
RIP: 0010:[<ffffffff81138e89>]  [<ffffffff81138e89>] 
__list_del_entry+0x29/0xc0
RSP: 0018:ffff88000033fe30  EFLAGS: 00010207
RAX: 0000000000000000 RBX: ffffffff8138c108 RCX: dead000000000200
RDX: 0000000000000000 RSI: 0000000000000061 RDI: ffffffff8138c108
RBP: ffff88000033fe30 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: ffffffff8138b928
R13: ffffffff8138c040 R14: ffff88000ec0da20 R15: ffff88000033ff58
FS:  00007ffff7ff2740(0000) GS:ffffffff8135d000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 0000000000335000 CR4: 00000000001406b0
Stack:
 ffff88000033fe48 ffffffff81138f2d ffffffff8138bbd0 ffff88000033fe70
 ffffffff811c880b ffff8800002f3000 ffff88000ec109a0 ffff880000298aa0
 ffff88000033fe88 ffffffff811ce040 ffff88000034cdc0 ffff88000033feb8
Call Trace:
 [<ffffffff81138f2d>] list_del+0xd/0x30
 [<ffffffff811c880b>] usb_gadget_unregister_driver+0xdb/0xf0
 [<ffffffff811ce040>] dev_release+0x20/0x60
 [<ffffffff810b464c>] __fput+0x4c/0x130
 [<ffffffff810b4769>] ____fput+0x9/0x10
 [<ffffffff81048577>] task_work_run+0x67/0xa0
 [<ffffffff81000dcf>] exit_to_usermode_loop+0x8f/0xa0
 [<ffffffff8100105d>] syscall_return_slowpath+0x3d/0x40
 [<ffffffff81278b89>] int_ret_from_sys_call+0x25/0x8f
Code: ff ff 55 48 8b 07 48 b9 00 01 00 00 00 00 ad de 48 8b 57 08 48 89 
e5 48 39 c8 74 29 48 b9 00 02 00 00 00 00 ad de 48 39 ca 74 3a <4c> 8b 
02 4c 39 c7 75 52 4c 8b 40 08 4c 39 c7 75 66 48 89 50 08
RIP  [<ffffffff81138e89>] __list_del_entry+0x29/0xc0
 RSP <ffff88000033fe30>
CR2: 0000000000000000
---[ end trace e6cfe1de661dcffe ]---

Reverting this commit fixes the problem for me:

commit 855ed04a3758b205e84b269f92d26ab36ed8e2f7
Author: Ruslan Bilovol <ruslan.bilovol@xxxxxxxxx>
Date:   Mon Nov 23 09:56:38 2015 +0100

    usb: gadget: udc-core: independent registration of gadgets and 
gadget drivers

Though I am still seeing some occasional lockups. Thanks,


Vegard