Re: [PATCH v2] driver: iio: add missing checks on iio_info's callback access

From: Julien Stephan
Date: Wed May 29 2024 - 09:11:18 EST

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Le mer. 29 mai 2024 à 14:05, Jonathan Cameron
<Jonathan.Cameron@xxxxxxxxxx> a écrit :
>
> On Wed, 29 May 2024 13:55:52 +0200
> Julien Stephan <jstephan@xxxxxxxxxxxx> wrote:
>
> > Some callbacks from iio_info structure are accessed without any check, so
> > if a driver doesn't implement them trying to access the corresponding
> > sysfs entries produce a kernel oops such as:
> >
> > [ 2203.527791] Unable to handle kernel NULL pointer dereference at virtual address 00000000 when execute
> > [...]
> > [ 2203.783416] Call trace:
> > [ 2203.783429] iio_read_channel_info_avail from dev_attr_show+0x18/0x48
> > [ 2203.789807] dev_attr_show from sysfs_kf_seq_show+0x90/0x120
> > [ 2203.794181] sysfs_kf_seq_show from seq_read_iter+0xd0/0x4e4
> > [ 2203.798555] seq_read_iter from vfs_read+0x238/0x2a0
> > [ 2203.802236] vfs_read from ksys_read+0xa4/0xd4
> > [ 2203.805385] ksys_read from ret_fast_syscall+0x0/0x54
> > [ 2203.809135] Exception stack(0xe0badfa8 to 0xe0badff0)
> > [ 2203.812880] dfa0: 00000003 b6f10f80 00000003 b6eab000 00020000 00000000
> > [ 2203.819746] dfc0: 00000003 b6f10f80 7ff00000 00000003 00000003 00000000 00020000 00000000
> > [ 2203.826619] dfe0: b6e1bc88 bed80958 b6e1bc94 b6e1bcb0
> > [ 2203.830363] Code: bad PC value
> > [ 2203.832695] ---[ end trace 0000000000000000 ]---
> >
> > Reviewed-by: Nuno Sa <nuno.sa@xxxxxxxxxx>
> > Signed-off-by: Julien Stephan <jstephan@xxxxxxxxxxxx>
>
> How bad would a registration time check look?
> I'd rather catch this early than have drivers with missing hooks
> that we don't notice because no one pokes the file.

Hi Jonathan,

Do you mean something like that (as it is done for ext_info for example) :

ret = __iio_add_chan_devattr(iio_chan_info_postfix[i],
chan,
- &iio_read_channel_info,
- &iio_write_channel_info,
+ indio_dev->info->read_raw ?
+ &iio_read_channel_info : NULL,
+ indio_dev->info->write_raw ?
+ &iio_write_channel_info : NULL,
i,
shared_by,
&indio_dev->dev,
NULL,
&iio_dev_opaque->channel_attr_list);

Or do you want to check even before and do not create the sysfs
entry if there is no callback registered by the driver?

Julien

>
> The inkern ones are good though.
>
> Jonathan
>
> > ---
> > Changes in v2:
> > - crop dmesg log to show only pertinent info and reduce commit message
> > - Link to v1: https://lore.kernel.org/r/20240529-iio-core-fix-segfault-v1-1-7ff1ba881d38@xxxxxxxxxxxx
> > ---
> > drivers/iio/industrialio-core.c | 7 ++++++-
> > drivers/iio/industrialio-event.c | 9 +++++++++
> > drivers/iio/inkern.c | 16 +++++++++++-----
> > 3 files changed, 26 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
> > index fa7cc051b4c4..2f185b386949 100644
> > --- a/drivers/iio/industrialio-core.c
> > +++ b/drivers/iio/industrialio-core.c
> > @@ -758,9 +758,11 @@ static ssize_t iio_read_channel_info(struct device *dev,
> > INDIO_MAX_RAW_ELEMENTS,
> > vals, &val_len,
> > this_attr->address);
> > - else
> > + else if (indio_dev->info->read_raw)
> > ret = indio_dev->info->read_raw(indio_dev, this_attr->c,
> > &vals[0], &vals[1], this_attr->address);
> > + else
> > + return -EINVAL;
> >
> > if (ret < 0)
> > return ret;
> > @@ -842,6 +844,9 @@ static ssize_t iio_read_channel_info_avail(struct device *dev,
> > int length;
> > int type;
> >
> > + if (!indio_dev->info->read_avail)
> > + return -EINVAL;
> > +
> > ret = indio_dev->info->read_avail(indio_dev, this_attr->c,
> > &vals, &type, &length,
> > this_attr->address);
> > diff --git a/drivers/iio/industrialio-event.c b/drivers/iio/industrialio-event.c
> > index 910c1f14abd5..a64f8fbac597 100644
> > --- a/drivers/iio/industrialio-event.c
> > +++ b/drivers/iio/industrialio-event.c
> > @@ -285,6 +285,9 @@ static ssize_t iio_ev_state_store(struct device *dev,
> > if (ret < 0)
> > return ret;
> >
> > + if (!indio_dev->info->write_event_config)
> > + return -EINVAL;
> > +
> > ret = indio_dev->info->write_event_config(indio_dev,
> > this_attr->c, iio_ev_attr_type(this_attr),
> > iio_ev_attr_dir(this_attr), val);
> > @@ -300,6 +303,9 @@ static ssize_t iio_ev_state_show(struct device *dev,
> > struct iio_dev_attr *this_attr = to_iio_dev_attr(attr);
> > int val;
> >
> > + if (!indio_dev->info->read_event_config)
> > + return -EINVAL;
> > +
> > val = indio_dev->info->read_event_config(indio_dev,
> > this_attr->c, iio_ev_attr_type(this_attr),
> > iio_ev_attr_dir(this_attr));
> > @@ -318,6 +324,9 @@ static ssize_t iio_ev_value_show(struct device *dev,
> > int val, val2, val_arr[2];
> > int ret;
> >
> > + if (!indio_dev->info->read_event_value)
> > + return -EINVAL;
> > +
> > ret = indio_dev->info->read_event_value(indio_dev,
> > this_attr->c, iio_ev_attr_type(this_attr),
> > iio_ev_attr_dir(this_attr), iio_ev_attr_info(this_attr),
> > diff --git a/drivers/iio/inkern.c b/drivers/iio/inkern.c
> > index 52d773261828..74f87f6ac390 100644
> > --- a/drivers/iio/inkern.c
> > +++ b/drivers/iio/inkern.c
> > @@ -560,9 +560,11 @@ static int iio_channel_read(struct iio_channel *chan, int *val, int *val2,
> > vals, &val_len, info);
> > *val = vals[0];
> > *val2 = vals[1];
> > - } else {
> > + } else if (chan->indio_dev->info->read_raw) {
> > ret = chan->indio_dev->info->read_raw(chan->indio_dev,
> > chan->channel, val, val2, info);
> > + } else {
> > + return -EINVAL;
> > }
> >
> > return ret;
> > @@ -753,8 +755,10 @@ static int iio_channel_read_avail(struct iio_channel *chan,
> > if (!iio_channel_has_available(chan->channel, info))
> > return -EINVAL;
> >
> > - return chan->indio_dev->info->read_avail(chan->indio_dev, chan->channel,
> > - vals, type, length, info);
> > + if (chan->indio_dev->info->read_avail)
> > + return chan->indio_dev->info->read_avail(chan->indio_dev, chan->channel,
> > + vals, type, length, info);
> > + return -EINVAL;
> > }
> >
> > int iio_read_avail_channel_attribute(struct iio_channel *chan,
> > @@ -917,8 +921,10 @@ EXPORT_SYMBOL_GPL(iio_get_channel_type);
> > static int iio_channel_write(struct iio_channel *chan, int val, int val2,
> > enum iio_chan_info_enum info)
> > {
> > - return chan->indio_dev->info->write_raw(chan->indio_dev,
> > - chan->channel, val, val2, info);
> > + if (chan->indio_dev->info->write_raw)
> > + return chan->indio_dev->info->write_raw(chan->indio_dev,
> > + chan->channel, val, val2, info);
> > + return -EINVAL;
> > }
> >
> > int iio_write_channel_attribute(struct iio_channel *chan, int val, int val2,
> >
> > ---
> > base-commit: 409b6d632f5078f3ae1018b6e43c32f2e12f6736
> > change-id: 20240528-iio-core-fix-segfault-aa74be7eee4a
> >
> > Best regards,
>

Next message: wangshuaijie: "[PATCH V1 0/5] Add support for Awinic SAR sensor."
Previous message: kernel test robot: "Re: [PATCH 1/3] mctp pcc: Implement MCTP over PCC Transport"
In reply to: Jonathan Cameron: "Re: [PATCH v2] driver: iio: add missing checks on iio_info's callback access"
Next in thread: Jonathan Cameron: "Re: [PATCH v2] driver: iio: add missing checks on iio_info's callback access"
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