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

DISCUSSION Pavel Machek 3 participants 3 messages Jul 30, 2019 – Aug 1, 2019

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Pavel Machek

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#0 lore raw

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;
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#1 lore raw

Hi Pavel,

Quoted 9 lines

From: Pavel Machek, Sent: Tuesday, July 30, 2019 6:52 PM

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.

Thank you for the report. I think the driver should use sysfs_streq() helper instead of strncmp() on the sysfs function. So, I'll submit such a patch later.

Best regards,
Yoshihiro Shimoda

Quoted 25 lines

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

#2 lore raw
In reply to Pavel Machek
Quoted 5 lines · Pavel Machek

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.

Quoted 1 line

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.

Quoted 23 lines

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;

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