Re: [PATCH] thunderbolt: Fix NULL pointer dereference in tb_port_update_credits()

[Mika Westerberg <mika.westerberg@linux.intel.com>]

On Mon, Feb 12, 2024 at 01:15:18PM +0100, Olliver Schinagl wrote:
> Hey Mika,
> 
> On 12-02-2024 12:51, Mika Westerberg wrote:
> > Olliver reported that his system crashes when plugging in Thunderbolt 1
> > device:
> > 
> >   BUG: kernel NULL pointer dereference, address: 0000000000000020
> >   #PF: supervisor read access in kernel mode
> >   #PF: error_code(0x0000) - not-present page
> >   PGD 0 P4D 0
> >   Oops: 0000 [#1] PREEMPT SMP NOPTI
> >   RIP: 0010:tb_port_do_update_credits+0x1b/0x130 [thunderbolt]
> >   Call Trace:
> >    <TASK>
> >    ? __die+0x23/0x70
> >    ? page_fault_oops+0x171/0x4e0
> >    ? exc_page_fault+0x7f/0x180
> >    ? asm_exc_page_fault+0x26/0x30
> >    ? tb_port_do_update_credits+0x1b/0x130
> >    ? tb_switch_update_link_attributes+0x83/0xd0
> >    tb_switch_add+0x7a2/0xfe0
> >    tb_scan_port+0x236/0x6f0
> >    tb_handle_hotplug+0x6db/0x900
> >    process_one_work+0x171/0x340
> >    worker_thread+0x27b/0x3a0
> >    ? __pfx_worker_thread+0x10/0x10
> >    kthread+0xe5/0x120
> >    ? __pfx_kthread+0x10/0x10
> >    ret_from_fork+0x31/0x50
> >    ? __pfx_kthread+0x10/0x10
> >    ret_from_fork_asm+0x1b/0x30
> >    </TASK>
> > 
> > This is due the fact that some Thunderbolt 1 devices only have one lane
> > adapter. Fix this by checking for the lane 1 before we read its credits.
> > 
> > Reported-by: Olliver Schinagl <oliver@schinagl.nl>
> > Closes: https://lore.kernel.org/linux-usb/c24c7882-6254-4e68-8f22-f3e8f65dc84f@schinagl.nl/
> > Fixes: 81af2952e606 ("thunderbolt: Add support for asymmetric link")
> > Cc: stable@vger.kernel.org
> > Cc: Gil Fine <gil.fine@linux.intel.com>
> > Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
> > ---
> > Hi Olliver,
> > 
> > I managed to reproduce this with a Thunderbolt 1 device. I wonder if you
> > can try this patch and see if it fixes your issue too?
> 
> That sounds reasonable, as it's an old Macbook (Should be TB2) with an old
> ethernet dongle (probably TB1?) or simply because it doesn't need that much
> speed (gbit adapter only). Sadly patching my kernel is not something I can
> do at the moment.

Right, if you plug in a TB1 device into TB2 host, that's also same issue
(TB1 devices don't always have two lane adapters).

It's fine if you cannot test this (but let me know if you want
instructions). I can pick this into my fixes branch and send for -rc. It
should land the arch Linux kernel tree at some point too, so you get it
by upgrading the kernel.