Re: [Linux kernel bug] general protection fault in disable_store

[Alan Stern <stern@rowland.harvard.edu>]

On Thu, Apr 11, 2024 at 02:52:27PM +0800, Sam Sun wrote:
> Dear developers and maintainers,
> 
> We encountered a general protection fault in function disable_store.
> It is tested against the latest upstream linux (tag 6.9-rc3). C repro
> and kernel config are attached to this email. Kernel crash log is
> listed below.
> ```
> general protection fault, probably for non-canonical address
> 0xdffffc0000000000: 0000 [#1] PREEMPT SMP KASAN
> KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
> CPU: 1 PID: 9459 Comm: syz-executor414 Not tainted 6.7.0-rc7 #2
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
> RIP: 0010:disable_store+0xd0/0x3d0 drivers/usb/core/port.c:88
> Code: 02 00 00 4c 8b 75 40 4d 8d be 58 ff ff ff 4c 89 ff e8 a4 20 fa
> ff 48 89 c2 48 89 c5 48 b8 00 00 00 00 00 fc ff df 48 c1 ea 03 <80> 3c
> 02 00 0f 85 b0 02 00 00 48 8b 45 00 48 8d bb 34 05 00 00 48
> RSP: 0018:ffffc90006e3fc08 EFLAGS: 00010246
> RAX: dffffc0000000000 RBX: ffff88801d4d4008 RCX: ffffffff86706be8
> RDX: 0000000000000000 RSI: ffffffff86706c4d RDI: 0000000000000005
> RBP: 0000000000000000 R08: 0000000000000005 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000000 R12: 1ffff92000dc7f85
> R13: ffff88810f4bfb18 R14: ffff88801d4d10a8 R15: ffff88801d4d1000
> FS:  00007fa0af71b640(0000) GS:ffff888135c00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007fa0af71a4b8 CR3: 0000000022f5f000 CR4: 0000000000750ef0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> PKRU: 55555554

> ----------------
> Code disassembly (best guess):
>    0:    02 00                    add    (%rax),%al
>    2:    00 4c 8b 75              add    %cl,0x75(%rbx,%rcx,4)
>    6:    40                       rex
>    7:    4d 8d be 58 ff ff ff     lea    -0xa8(%r14),%r15
>    e:    4c 89 ff                 mov    %r15,%rdi
>   11:    e8 a4 20 fa ff           call   0xfffa20ba
>   16:    48 89 c2                 mov    %rax,%rdx
>   19:    48 89 c5                 mov    %rax,%rbp
>   1c:    48 b8 00 00 00 00 00     movabs $0xdffffc0000000000,%rax
>   23:    fc ff df
>   26:    48 c1 ea 03              shr    $0x3,%rdx
> * 2a:    80 3c 02 00              cmpb   $0x0,(%rdx,%rax,1) <--
> trapping instruction
>   2e:    0f 85 b0 02 00 00        jne    0x2e4
>   34:    48 8b 45 00              mov    0x0(%rbp),%rax
>   38:    48 8d bb 34 05 00 00     lea    0x534(%rbx),%rdi
>   3f:    48                       rex.W
> ```
> We analyzed the root cause of this bug. When calling disable_store()
> in drivers/usb/core/port.c, if function authorized_store() is calling
> usb_deauthorized_device() concurrently, the usb_interface will be
> removed by usb_disable_device. However, in function disable_store,
> usb_hub_to_struct_hub() would try to deref interface, causing
> nullptr-deref. We also tested other functions in
> drivers/usb/core/port.c. So far we haven't found a similar problem.

I don't see how this explanation could be correct.  disable_store() is a 
sysfs attribute file for the port device, so when it is called the port 
device structure must still be registered.  The interface structure 
doesn't get removed until after usb_disable_device() calls device_del(), 
which won't return until hub_disconnect() returns, which won't happen 
until after the port devices are unregistered, which doesn't happen 
until disable_store() calls sysfs_break_active_protection(), which is 
after the call to usb_hub_to_struct_hub().

Can you do a little extra debugging to find out exactly which C 
statement causes the trap?  The disassembly above indicates the trap 
happens during a compare against 0 inside disable_store() -- not inside 
usb_hub_to_struct_hub().  Can you figure out which comparison that is?

Alan Stern

> If you have any questions, please contact us.
> 
> Reported by Yue Sun <samsun1006219@gmail.com>
> Reported by xingwei lee <xrivendell7@gmail.com>
> 
> Best Regards,
> Yue