netdev - Re: [PATCH] net: dsa: microchip: fix NULL pointer dereference in ksz_connect_tag

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Date: Wed, 6 Dec 2023 15:46:23 +0100
From: Sean Nyekjaer <sean@...nix.com>
To: Madhuri.Sripada@...rochip.com
Cc: Woojung.Huh@...rochip.com,
 UNGLinuxDriver@...rochip.com,
 andrew@...n.ch,
 ceggers@...i.de,
 netdev@...r.kernel.org
Subject: Re: [PATCH] net: dsa: microchip: fix NULL pointer dereference in
 ksz_connect_tag_protocol()



> On 6 Dec 2023, at 14.35, <Madhuri.Sripada@...rochip.com> <Madhuri.Sripada@...rochip.com> wrote:
> 
> Hi Sean
> 
> -----Original Message-----
> From: Sean Nyekjaer <sean@...nix.com> 
> Sent: Tuesday, December 5, 2023 6:17 PM
> To: Woojung Huh - C21699 <Woojung.Huh@...rochip.com>; UNGLinuxDriver <UNGLinuxDriver@...rochip.com>; andrew@...n.ch; ceggers@...i.de; netdev@...r.kernel.org
> Cc: Sean Nyekjaer <sean@...nix.com>
> Subject: [PATCH] net: dsa: microchip: fix NULL pointer dereference in ksz_connect_tag_protocol()
> 
> [Some people who received this message don't often get email from sean@...nix.com. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]
> 
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> We should check whether the ksz_tagger_data is allocated.
> For example when using DSA_TAG_PROTO_KSZ8795 protocol, ksz_connect() is not allocating ksz_tagger_data.
> 
> This avoids the following null pointer dereference:
> Unable to handle kernel NULL pointer dereference at virtual address 00000000 when write [00000000] *pgd=00000000 Internal error: Oops: 817 [#1] PREEMPT SMP ARM Modules linked in:
> CPU: 1 PID: 26 Comm: kworker/u5:1 Not tainted 6.6.0 Hardware name: STM32 (Device Tree Support)
> Workqueue: events_unbound deferred_probe_work_func PC is at ksz_connect_tag_protocol+0x40/0x48
> LR is at ksz_connect_tag_protocol+0x3c/0x48
> [ ... ]
> ksz_connect_tag_protocol from dsa_register_switch+0x9ac/0xee0  dsa_register_switch from ksz_switch_register+0x65c/0x828  ksz_switch_register from ksz_spi_probe+0x11c/0x168  ksz_spi_probe from spi_probe+0x84/0xa8  spi_probe from really_probe+0xc8/0x2d8
> 
> Fixes: ab32f56a4100 ("net: dsa: microchip: ptp: add packet transmission timestamping")
> Signed-off-by: Sean Nyekjaer <sean@...nix.com>
> ---
> drivers/net/dsa/microchip/ksz_common.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/dsa/microchip/ksz_common.c b/drivers/net/dsa/microchip/ksz_common.c
> index 42db7679c360..1b9815418294 100644
> --- a/drivers/net/dsa/microchip/ksz_common.c
> +++ b/drivers/net/dsa/microchip/ksz_common.c
> @@ -2623,9 +2623,10 @@ static int ksz_connect_tag_protocol(struct dsa_switch *ds,
>                                    enum dsa_tag_protocol proto)  {
>        struct ksz_tagger_data *tagger_data;
> -
> -       tagger_data = ksz_tagger_data(ds);
> -       tagger_data->xmit_work_fn = ksz_port_deferred_xmit;
> +       if (ksz_tagger_data(ds)) {
> +               tagger_data = ksz_tagger_data(ds);
> +               tagger_data->xmit_work_fn = ksz_port_deferred_xmit;
> +       }
> 
>        return 0;
> }
> --
> 2.42.0
> 
> 
> Instead of calling " ksz_tagger_data(ds)" twice, NULL check tagger_data before assigning " xmit_work_fn" would help right?
> Is there any reason for doing this way?

I have submitted a v2 of this patch:
https://lore.kernel.org/netdev/20231206071655.1626479-1-sean@geanix.com/T/#u

/Sean