2019-07-30 15:39:36

by Pavel Machek

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Subject: phy-rcar-gen3-usb2: wrong parsing of role in role_store?

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Hi!

Code does strcmps, but does not actually check count. So AFAICT
writing "host-I-don't-want-I-need-peripheral" into the file will
succeed and turn it into host mode.

Also data beyond count in buf are going to be accessed.

Best regards,
Pavel

static ssize_t role_store(struct device *dev, struct device_attribute *attr,
const char *buf, size_t count)
{
struct rcar_gen3_chan *ch = dev_get_drvdata(dev);
bool is_b_device;
enum phy_mode cur_mode, new_mode;

if (!ch->is_otg_channel || !rcar_gen3_is_any_rphy_initialized(ch))
return -EIO;

/* FIXME, this is wrong */
if (!strncmp(buf, "host", strlen("host")))
new_mode = PHY_MODE_USB_HOST;
else if (!strncmp(buf, "peripheral", strlen("peripheral")))
new_mode = PHY_MODE_USB_DEVICE;
else
return -EINVAL;


--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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2019-08-01 23:46:23

by Ben Hutchings

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Subject: Re: [cip-dev] phy-rcar-gen3-usb2: wrong parsing of role in role_store?

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On Tue, 2019-07-30 at 11:51 +0200, Pavel Machek wrote:
> Hi!
>
> Code does strcmps, but does not actually check count. So AFAICT
> writing "host-I-don't-want-I-need-peripheral" into the file will
> succeed and turn it into host mode.

I suspect the intent is to work without a trailing "\n", but you're
right that this parsing is rather lax.

> Also data beyond count in buf are going to be accessed.

All attribute writes should be going through kernfs_fop_write(), which
writes a null terminator at buf[count] before calling the write/store
function. (I don't know where that'ss documented though.) So I think
this is safe.

Ben.

> static ssize_t role_store(struct device *dev, struct device_attribute *attr,
> const char *buf, size_t count)
> {
> struct rcar_gen3_chan *ch = dev_get_drvdata(dev);
> bool is_b_device;
> enum phy_mode cur_mode, new_mode;
>
> if (!ch->is_otg_channel || !rcar_gen3_is_any_rphy_initialized(ch))
> return -EIO;
>
> /* FIXME, this is wrong */
> if (!strncmp(buf, "host", strlen("host")))
> new_mode = PHY_MODE_USB_HOST;
> else if (!strncmp(buf, "peripheral", strlen("peripheral")))
> new_mode = PHY_MODE_USB_DEVICE;
> else
> return -EINVAL;
>
>
> _______________________________________________
> cip-dev mailing list
> [email protected]
> https://lists.cip-project.org/mailman/listinfo/cip-dev
--
Ben Hutchings, Software Developer Codethink Ltd
https://www.codethink.co.uk/ Dale House, 35 Dale Street
Manchester, M1 2HF, United Kingdom