Re: [PATCH] tty: serial: jsm: add checks against NULL pointer dereference

[Greg KH <gregkh@linuxfoundation.org>]

On Thu, Jun 03, 2021 at 06:41:20AM +0000, Zheyu Ma wrote:
> In function 'neo_intr', the driver uses 'ch->ch_equeue' and
> 'ch->ch_reuque'. These two pointers are initialized in 'jsm_tty_open',
> but the interrupt handler 'neo_intr' has been registered in the probe
> progress. If 'jsm_tty_open' has not been called at this time, it will
> cause null pointer dereference.
> 
> Once the driver registers the interrupt handler, the driver should be
> ready to handle it.
> 
> Fix this by checking whether it is a null pointer.
> 
> This log reveals it:
> 
> [   50.934983] BUG: kernel NULL pointer dereference, address:
> 0000000000000000
> [   50.938297] #PF: supervisor write access in kernel mode
> [   50.940075] #PF: error_code(0x0002) - not-present page
> [   50.940460] PGD 0 P4D 0
> [   50.940654] Oops: 0002 [#1] PREEMPT SMP PTI
> [   50.940967] CPU: 2 PID: 0 Comm: swapper/2 Not tainted
> 5.12.4-g70e7f0549188-dirty #97
> [   50.941554] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009),
> BIOS rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014
> [   50.942419] RIP: 0010:memcpy_fromio+0x75/0xa0
> [   50.942759] Code: e9 02 f3 a5 41 f6 c5 02 74 02 66 a5 41 f6 c5 01 74
> 01 a4 e8 5d 93 6b ff 5b 41 5c 41 5d 5d c3 e8 51 93 6b ff 4c 89 e7 48 89
> de <a4> 49 89 fc 48 89 f3 49 83 ed 01 eb a4 e8 39 93 6b ff 4c 89 e7 48
> [   50.944158] RSP: 0018:ffffc90000118df8 EFLAGS: 00010046
> [   50.944559] RAX: ffff888100258000 RBX: ffffc90007f0030f
> RCX: 0000000000000000
> [   50.945114] RDX: 0000000000000000 RSI: ffffc90007f0030f
> RDI: 0000000000000000
> [   50.945652] RBP: ffffc90000118e10 R08: 0000000000000000
> R09: 0000000000000000
> [   50.946192] R10: 0000000000000000 R11: 0000000000000001
> R12: 0000000000000000
> [   50.946729] R13: 0000000000000001 R14: 0000000007f0021e
> R15: 0000000000000000
> [   50.947279] FS:  0000000000000000(0000) GS:ffff88817bc80000(0000)
> knlGS:0000000000000000
> [   50.947912] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [   50.948346] CR2: 0000000000000000 CR3: 0000000107950000
> CR4: 00000000000006e0
> [   50.948892] DR0: 0000000000000000 DR1: 0000000000000000
> DR2: 0000000000000000
> [   50.949429] DR3: 0000000000000000 DR6: 00000000fffe0ff0
> DR7: 0000000000000400
> [   50.949950] Call Trace:
> [   50.950138]  <IRQ>
> [   50.950292]  neo_copy_data_from_uart_to_queue+0x2f7/0x4e0
> [   50.950694]  neo_intr+0x253/0x7a0
> [   50.950975]  __handle_irq_event_percpu+0x53/0x3e0
> [   50.951352]  handle_irq_event_percpu+0x35/0x90
> [   50.951706]  handle_irq_event+0x39/0x60
> [   50.951999]  handle_fasteoi_irq+0xc2/0x1d0
> [   50.952319]  __common_interrupt+0x7f/0x150
> [   50.952638]  common_interrupt+0xb4/0xd0
> [   50.952954]  </IRQ>
> [   50.953136]  asm_common_interrupt+0x1e/0x40
> [   50.969513] Kernel panic - not syncing: Fatal exception in interrupt
> [   50.970151] Dumping ftrace buffer:
> [   50.970420]    (ftrace buffer empty)
> [   50.970693] Kernel Offset: disabled
> [   50.970968] Rebooting in 1 seconds..
> 
> Signed-off-by: Zheyu Ma <zheyuma97@gmail.com>
> ---
>  drivers/tty/serial/jsm/jsm_neo.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/tty/serial/jsm/jsm_neo.c b/drivers/tty/serial/jsm/jsm_neo.c
> index bf0e2a4cb0ce..46be0b53ab42 100644
> --- a/drivers/tty/serial/jsm/jsm_neo.c
> +++ b/drivers/tty/serial/jsm/jsm_neo.c
> @@ -716,7 +716,7 @@ static void neo_parse_isr(struct jsm_board *brd, u32 port)
>  		return;
>  
>  	ch = brd->channels[port];
> -	if (!ch)
> +	if (!ch || !ch->ch_equeue || !ch->ch_rqueue)
>  		return;

Why not just allocate the memory at probe time and not at open time?
That would resolve this issue, and probably any other problems that are
only caused by initializing things at open time.

Once the interrupt is registered, it HAS to be able to be called,
otherwise it is a driver bug.  This change keeps that broken logic still
happening and just papers over the obvious crash.

Can you fix this the correct way instead please?

thanks,

greg k-h