linux-kernel - Re: [PATCH] ata: libata: fix ALL_SUB_MPAGES not to be performed when CDL is not supported

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Message-ID: <CAO9qdTGAgBux-M3GxZdBbBpsUm0V_E8fyWSjZuA7jA8bH-Qf4g@mail.gmail.com>
Date: Mon, 23 Sep 2024 20:15:59 +0900
From: Jeongjun Park <aha310510@...il.com>
To: Damien Le Moal <dlemoal@...nel.org>
Cc: cassel@...nel.org, syzbot+37757dc11ee77ef850bb@...kaller.appspotmail.com, 
	linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ata: libata: fix ALL_SUB_MPAGES not to be performed when
 CDL is not supported

Damien Le Moal <dlemoal@...nel.org> wrote:
>
> On 2024/09/21 14:41, Jeongjun Park wrote:
> > In the previous commit 602bcf212637 ("ata: libata: Improve CDL resource
> > management"), the ata_cdl structure was added and the ata_cdl structure
> > memory was allocated with kzalloc(). Because of this, if CDL is not
> > supported, dev->cdl is a NULL pointer, so additional work should never
> > be done.
> >
> > However, even if CDL is not supported now, if spg is ALL_SUB_MPAGES,
> > dereferencing dev->cdl will result in a NULL pointer dereference.
> >
> > Therefore, I think it is appropriate to check dev->flags in
> > ata_scsiop_mode_sense() if spg is ALL_SUB_MPAGES to see if CDL is supported.
> >
> > Reported-by: syzbot+37757dc11ee77ef850bb@...kaller.appspotmail.com
> > Tested-by: syzbot+37757dc11ee77ef850bb@...kaller.appspotmail.com
> > Fixes: 602bcf212637 ("ata: libata: Improve CDL resource management")
> > Signed-off-by: Jeongjun Park <aha310510@...il.com>
> > ---
> >  drivers/ata/libata-scsi.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
> > index 3328a6febc13..6f5527f12b0e 100644
> > --- a/drivers/ata/libata-scsi.c
> > +++ b/drivers/ata/libata-scsi.c
> > @@ -2442,7 +2442,9 @@ static unsigned int ata_scsiop_mode_sense(struct ata_scsi_args *args, u8 *rbuf)
> >       if (spg) {
> >               switch (spg) {
> >               case ALL_SUB_MPAGES:
> > -                     break;
> > +                     if (dev->flags & ATA_DFLAG_CDL)
> > +                             break;
> > +                     fallthrough;
>
> I do not think this is correct at all. If the user request all sub mpages, we
> need to give that list regardless of CDL support. What needs to be fixed is that
> if CDL is NOT supported, we should not try to add the information for the T2A
> and T2B sub pages. So the fix should be this:

Okay. But after looking into it further, I think it would be more appropriate to
also check the ATA_DFLAG_CDL_ENABLED flag when checking if CDL is
not supported. So it seems like it would be better to modify the condition as
below.

What do you think?

if (!(dev->flags & ATA_DFLAG_CDL
      dev->flags & ATA_DFLAG_CDL_ENABLED) || !dev->cdl)
        return 0;

Regards,
Jeongjun Park

>
> diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
> index 3328a6febc13..6ffa975746a6 100644
> --- a/drivers/ata/libata-scsi.c
> +++ b/drivers/ata/libata-scsi.c
> @@ -2256,10 +2256,15 @@ static inline u16 ata_xlat_cdl_limit(u8 *buf)
>  static unsigned int ata_msense_control_spgt2(struct ata_device *dev, u8 *buf,
>                                              u8 spg)
>  {
> -       u8 *b, *cdl = dev->cdl->desc_log_buf, *desc;
> +       u8 *b, *cdl, *desc;
>         u32 policy;
>         int i;
>
> +       if (!(dev->flags & ATA_DFLAG_CDL) || !dev->cdl)
> +               return 0;
> +
> +       cdl = dev->cdl->desc_log_buf;
> +
>         /*
>          * Fill the subpage. The first four bytes of the T2A/T2B mode pages
>          * are a header. The PAGE LENGTH field is the size of the page
>
>
> >               case CDL_T2A_SUB_MPAGE:
> >               case CDL_T2B_SUB_MPAGE:
> >               case ATA_FEATURE_SUB_MPAGE:
> > --
>
> --
> Damien Le Moal
> Western Digital Research
>