[PATCH AUTOSEL 4.19 08/19] HID: roccat: Fix use-after-free in roccat_read()

Sasha Levin
2022-10-13T01:09:06Z

From: Hyunwoo Kim <imv4bel@gmail.com>

[ Upstream commit cacdb14b1c8d3804a3a7d31773bc7569837b71a4 ]

roccat_report_event() is responsible for registering
roccat-related reports in struct roccat_device.

int roccat_report_event(int minor, u8 const *data)
{
struct roccat_device *device;
struct roccat_reader *reader;
struct roccat_report *report;
uint8_t *new_value;

device = devices[minor];

new_value = kmemdup(data, device->report_size, GFP_ATOMIC);
if (!new_value)
return -ENOMEM;

report = &device->cbuf[device->cbuf_end];

/* passing NULL is safe */
kfree(report->value);
...

The registered report is stored in the struct roccat_device member
"struct roccat_report cbuf[ROCCAT_CBUF_SIZE];".
If more reports are received than the "ROCCAT_CBUF_SIZE" value,
kfree() the saved report from cbuf[0] and allocates a new reprot.
Since there is no lock when this kfree() is performed,
kfree() can be performed even while reading the saved report.

static ssize_t roccat_read(struct file *file, char __user *buffer,
size_t count, loff_t *ppos)
{
struct roccat_reader *reader = file->private_data;
struct roccat_device *device = reader->device;
struct roccat_report *report;
ssize_t retval = 0, len;
DECLARE_WAITQUEUE(wait, current);

mutex_lock(&device->cbuf_lock);

...

report = &device->cbuf[reader->cbuf_start];
/*
* If report is larger than requested amount of data, rest of report
* is lost!
*/
len = device->report_size > count ? count : device->report_size;

if (copy_to_user(buffer, report->value, len)) {
retval = -EFAULT;
goto exit_unlock;
}
...

The roccat_read() function receives the device->cbuf report and
delivers it to the user through copy_to_user().
If the N+ROCCAT_CBUF_SIZE th report is received while copying of
the Nth report->value is in progress, the pointer that copy_to_user()
is working on is kfree()ed and UAF read may occur. (race condition)

Since the device node of this driver does not set separate permissions,
this is not a security vulnerability, but because it is used for
requesting screen display of profile or dpi settings,
a user using the roccat device can apply udev to this device node or
There is a possibility to use it by giving.

Signed-off-by: Hyunwoo Kim <imv4bel@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/hid/hid-roccat.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/drivers/hid/hid-roccat.c b/drivers/hid/hid-roccat.c
index 5be8de70c651..c9cec00b4e6e 100644
--- a/drivers/hid/hid-roccat.c
+++ b/drivers/hid/hid-roccat.c
@@ -260,6 +260,8 @@ int roccat_report_event(int minor, u8 const *data)
if (!new_value)
return -ENOMEM;

+ mutex_lock(&device->cbuf_lock);
+
report = &device->cbuf[device->cbuf_end];

/* passing NULL is safe */
@@ -279,6 +281,8 @@ int roccat_report_event(int minor, u8 const *data)
reader->cbuf_start = (reader->cbuf_start + 1) % ROCCAT_CBUF_SIZE;
}

+ mutex_unlock(&device->cbuf_lock);
+
wake_up_interruptible(&device->wait);
return 0;
}
--
2.35.1