From: Reilly Grant <reillyg@xxxxxxxxxxxx>
The new USBDEVFS_DROP_PRIVILEGES ioctl allows a process to voluntarily
relinquish the ability to issue other ioctls that may interfere with
other processes and drivers that have claimed an interface on the
device.
This commit also includes a simple utility to be able to test the
ioctl, located at Documentation/usb/usbdevfs-drop-permissions.c
Example (with qemu-kvm's input device):
$ lsusb
...
Bus 001 Device 002: ID 0627:0001 Adomax Technology Co., Ltd
$ usb-devices
...
C: #Ifs= 1 Cfg#= 1 Atr=a0 MxPwr=100mA
I: If#= 0 Alt= 0 #EPs= 1 Cls=03(HID ) Sub=00 Prot=02 Driver=usbhid
$ sudo ./usbdevfs-drop-permissions /dev/bus/usb/001/002
OK: privileges dropped!
Available options:
[0] Exit now
[1] Reset device. Should fail if device is in use
[2] Claim 4 interfaces. Should succeed where not in use
[3] Narrow interface permission mask
Which option shall I run?: 1
ERROR: USBDEVFS_RESET failed! (1 - Operation not permitted)
Which test shall I run next?: 2
ERROR claiming if 0 (1 - Operation not permitted)
ERROR claiming if 1 (1 - Operation not permitted)
ERROR claiming if 2 (1 - Operation not permitted)
ERROR claiming if 3 (1 - Operation not permitted)
Which test shall I run next?: 0
After unbinding usbhid:
$ usb-devices
...
I: If#= 0 Alt= 0 #EPs= 1 Cls=03(HID ) Sub=00 Prot=02 Driver=(none)
$ sudo ./usbdevfs-drop-permissions /dev/bus/usb/001/002
...
Which option shall I run?: 2
OK: claimed if 0
ERROR claiming if 1 (1 - Operation not permitted)
ERROR claiming if 2 (1 - Operation not permitted)
ERROR claiming if 3 (1 - Operation not permitted)
Which test shall I run next?: 1
OK: USBDEVFS_RESET succeeded
Which test shall I run next?: 0
After unbinding usbhid and restricting the mask:
$ sudo ./usbdevfs-drop-permissions /dev/bus/usb/001/002
...
Which option shall I run?: 3
Insert new mask: 0
OK: privileges dropped!
Which test shall I run next?: 2
ERROR claiming if 0 (1 - Operation not permitted)
ERROR claiming if 1 (1 - Operation not permitted)
ERROR claiming if 2 (1 - Operation not permitted)
ERROR claiming if 3 (1 - Operation not permitted)
Signed-off-by: Reilly Grant <reillyg@xxxxxxxxxxxx>
Acked-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Emilio López <emilio.lopez@xxxxxxxxxxxxxxx>
---
Changes in v5:
- rebased on usb-next, changing the capability flag value to not collide
- Added Alan's ack
Changes in v4:
- IOR -> IOW
- Explain the new ioctl on usb Docbook
- Small program to be able to test the new functionality
- New capability flag
- Allow people to reset devices if they are the only ones
claiming interfaces, as suggested by Alan
Changes in v3:
- Switch ioctl to use a __u32 given the iface qty is capped at 32
- Reword comments as requested by Alan
- Allow callers to shrink the allowed interfaces mask
Changes in v2:
- Added a parameter to the ioctl, a mask of interfaces an unprivileged
process is allowed to claim.
- Drop Tested-by's
Documentation/DocBook/usb.tmpl | 12 +++
Documentation/usb/usbdevfs-drop-permissions.c | 120 ++++++++++++++++++++++++++
drivers/usb/core/devio.c | 63 ++++++++++++--
include/uapi/linux/usbdevice_fs.h | 2 +
4 files changed, 192 insertions(+), 5 deletions(-)
create mode 100644 Documentation/usb/usbdevfs-drop-permissions.c
diff --git a/Documentation/DocBook/usb.tmpl b/Documentation/DocBook/usb.tmpl
index 4cd5b2c..bc776be0 100644
--- a/Documentation/DocBook/usb.tmpl
+++ b/Documentation/DocBook/usb.tmpl
@@ -732,6 +732,18 @@ usbdev_ioctl (int fd, int ifno, unsigned request, void *param)
or SET_INTERFACE.
</para></warning></listitem></varlistentry>
+ <varlistentry><term>USBDEVFS_DROP_PRIVILEGES</term>
+ <listitem><para>This is used to relinquish the ability
+ to do certain operations which are considered to be
+ privileged on a usbfs file descriptor.
+ This includes claiming arbitrary interfaces, resetting
+ a device on which there are currently claimed interfaces
+ from other users, and issuing USBDEVFS_IOCTL calls.
+ The ioctl parameter is a 32 bit mask of interfaces
+ the user is allowed to claim on this file descriptor.
+ You may issue this ioctl more than one time to narrow
+ said mask.
+ </para></listitem></varlistentry>
</variablelist>
</sect2>
diff --git a/Documentation/usb/usbdevfs-drop-permissions.c b/Documentation/usb/usbdevfs-drop-permissions.c
new file mode 100644
index 0000000..6b8da6e
--- /dev/null
+++ b/Documentation/usb/usbdevfs-drop-permissions.c
@@ -0,0 +1,120 @@
+#include <sys/ioctl.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <errno.h>
+#include <string.h>
+#include <inttypes.h>
+#include <unistd.h>
+
+#include <linux/usbdevice_fs.h>
+
+/* For building without an updated set of headers */
+#ifndef USBDEVFS_DROP_PRIVILEGES
+#define USBDEVFS_DROP_PRIVILEGES _IOW('U', 30, __u32)
+#define USBDEVFS_CAP_DROP_PRIVILEGES 0x40
+#endif
+
+void drop_privileges(int fd, uint32_t mask)
+{
+ int res;
+
+ res = ioctl(fd, USBDEVFS_DROP_PRIVILEGES, &mask);
+ if (res)
+ printf("ERROR: USBDEVFS_DROP_PRIVILEGES returned %d\n", res);
+ else
+ printf("OK: privileges dropped!\n");
+}
+
+void reset_device(int fd)
+{
+ int res;
+
+ res = ioctl(fd, USBDEVFS_RESET);
+ if (!res)
+ printf("OK: USBDEVFS_RESET succeeded\n");
+ else
+ printf("ERROR: reset failed! (%d - %s)\n",
+ -res, strerror(-res));
+}
+
+void claim_some_intf(int fd)
+{
+ int i, res;
+
+ for (i = 0; i < 4; i++) {
+ res = ioctl(fd, USBDEVFS_CLAIMINTERFACE, &i);
+ if (!res)
+ printf("OK: claimed if %d\n", i);
+ else
+ printf("ERROR claiming if %d (%d - %s)\n",
+ i, -res, strerror(-res));
+ }
+}
+
+int main(int argc, char *argv[])
+{
+ uint32_t mask, caps;
+ int c, fd;
+
+ fd = open(argv[1], O_RDWR);
+ if (fd < 0) {
+ printf("Failed to open file\n");
+ goto err_fd;
+ }
+
+ /*
+ * check if dropping privileges is supported,
+ * bail on systems where the capability is not present
+ */
+ ioctl(fd, USBDEVFS_GET_CAPABILITIES, &caps);
+ if (!(caps & USBDEVFS_CAP_DROP_PRIVILEGES)) {
+ printf("DROP_PRIVILEGES not supported\n");
+ goto err;
+ }
+
+ /*
+ * Drop privileges but keep the ability to claim all
+ * free interfaces (i.e., those not used by kernel drivers)
+ */
+ drop_privileges(fd, -1U);
+
+ printf("Available options:\n"
+ "[0] Exit now\n"
+ "[1] Reset device. Should fail if device is in use\n"
+ "[2] Claim 4 interfaces. Should succeed where not in use\n"
+ "[3] Narrow interface permission mask\n"
+ "Which option shall I run?: ");
+
+ while (scanf("%d", &c) == 1) {
+ switch (c) {
+ case 0:
+ goto exit;
+ case 1:
+ reset_device(fd);
+ break;
+ case 2:
+ claim_some_intf(fd);
+ break;
+ case 3:
+ printf("Insert new mask: ");
+ scanf("%x", &mask);
+ drop_privileges(fd, mask);
+ break;
+ default:
+ printf("I don't recognize that\n");
+ }
+
+ printf("Which test shall I run next?: ");
+ }
+
+exit:
+ close(fd);
+ return 0;
+
+err:
+ close(fd);
+err_fd:
+ return 1;
+}
diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c
index 39da166..52c4461 100644
--- a/drivers/usb/core/devio.c
+++ b/drivers/usb/core/devio.c
@@ -79,6 +79,8 @@ struct usb_dev_state {
unsigned long ifclaimed;
u32 secid;
u32 disabled_bulk_eps;
+ bool privileges_dropped;
+ unsigned long interface_allowed_mask;
};
struct usb_memory {
@@ -748,6 +750,10 @@ static int claimintf(struct usb_dev_state *ps, unsigned int ifnum)
if (test_bit(ifnum, &ps->ifclaimed))
return 0;
+ if (ps->privileges_dropped &&
+ !test_bit(ifnum, &ps->interface_allowed_mask))
+ return -EACCES;
+
intf = usb_ifnum_to_if(dev, ifnum);
if (!intf)
err = -ENOENT;
@@ -985,7 +991,7 @@ static int usbdev_open(struct inode *inode, struct file *file)
int ret;
ret = -ENOMEM;
- ps = kmalloc(sizeof(struct usb_dev_state), GFP_KERNEL);
+ ps = kzalloc(sizeof(struct usb_dev_state), GFP_KERNEL);
if (!ps)
goto out_free_ps;
@@ -1013,17 +1019,15 @@ static int usbdev_open(struct inode *inode, struct file *file)
ps->dev = dev;
ps->file = file;
+ ps->interface_allowed_mask = 0xFFFFFFFF; /* 32 bits */
spin_lock_init(&ps->lock);
INIT_LIST_HEAD(&ps->list);
INIT_LIST_HEAD(&ps->async_pending);
INIT_LIST_HEAD(&ps->async_completed);
INIT_LIST_HEAD(&ps->memory_list);
init_waitqueue_head(&ps->wait);
- ps->discsignr = 0;
ps->disc_pid = get_pid(task_pid(current));
ps->cred = get_current_cred();
- ps->disccontext = NULL;
- ps->ifclaimed = 0;
security_task_getsecid(current, &ps->secid);
smp_wmb();
list_add_tail(&ps->list, &dev->filelist);
@@ -1324,6 +1328,28 @@ static int proc_connectinfo(struct usb_dev_state *ps, void __user *arg)
static int proc_resetdevice(struct usb_dev_state *ps)
{
+ struct usb_host_config *actconfig = ps->dev->actconfig;
+ struct usb_interface *interface;
+ int i, number;
+
+ /* Don't allow a device reset if the process has dropped the
+ * privilege to do such things and any of the interfaces are
+ * currently claimed.
+ */
+ if (ps->privileges_dropped && actconfig) {
+ for (i = 0; i < actconfig->desc.bNumInterfaces; ++i) {
+ interface = actconfig->interface[i];
+ number = interface->cur_altsetting->desc.bInterfaceNumber;
+ if (usb_interface_claimed(interface) &&
+ !test_bit(number, &ps->ifclaimed)) {
+ dev_warn(&ps->dev->dev,
+ "usbfs: interface %d claimed by %s while '%s' resets device\n",
+ number, interface->dev.driver->name, current->comm);
+ return -EACCES;
+ }
+ }
+ }
+
return usb_reset_device(ps->dev);
}
@@ -2090,6 +2116,9 @@ static int proc_ioctl(struct usb_dev_state *ps, struct usbdevfs_ioctl *ctl)
struct usb_interface *intf = NULL;
struct usb_driver *driver = NULL;
+ if (ps->privileges_dropped)
+ return -EACCES;
+
/* alloc buffer */
size = _IOC_SIZE(ctl->ioctl_code);
if (size > 0) {
@@ -2215,7 +2244,8 @@ static int proc_get_capabilities(struct usb_dev_state *ps, void __user *arg)
__u32 caps;
caps = USBDEVFS_CAP_ZERO_PACKET | USBDEVFS_CAP_NO_PACKET_SIZE_LIM |
- USBDEVFS_CAP_REAP_AFTER_DISCONNECT | USBDEVFS_CAP_MMAP;
+ USBDEVFS_CAP_REAP_AFTER_DISCONNECT | USBDEVFS_CAP_MMAP |
+ USBDEVFS_CAP_DROP_PRIVILEGES;
if (!ps->dev->bus->no_stop_on_short)
caps |= USBDEVFS_CAP_BULK_CONTINUATION;
if (ps->dev->bus->sg_tablesize)
@@ -2242,6 +2272,9 @@ static int proc_disconnect_claim(struct usb_dev_state *ps, void __user *arg)
if (intf->dev.driver) {
struct usb_driver *driver = to_usb_driver(intf->dev.driver);
+ if (ps->privileges_dropped)
+ return -EACCES;
+
if ((dc.flags & USBDEVFS_DISCONNECT_CLAIM_IF_DRIVER) &&
strncmp(dc.driver, intf->dev.driver->name,
sizeof(dc.driver)) != 0)
@@ -2298,6 +2331,23 @@ static int proc_free_streams(struct usb_dev_state *ps, void __user *arg)
return r;
}
+static int proc_drop_privileges(struct usb_dev_state *ps, void __user *arg)
+{
+ u32 data;
+
+ if (copy_from_user(&data, arg, sizeof(data)))
+ return -EFAULT;
+
+ /* This is an one way operation. Once privileges are
+ * dropped, you cannot regain them. You may however reissue
+ * this ioctl to shrink the allowed interfaces mask.
+ */
+ ps->interface_allowed_mask &= data;
+ ps->privileges_dropped = true;
+
+ return 0;
+}
+
/*
* NOTE: All requests here that have interface numbers as parameters
* are assuming that somehow the configuration has been prevented from
@@ -2486,6 +2536,9 @@ static long usbdev_do_ioctl(struct file *file, unsigned int cmd,
case USBDEVFS_FREE_STREAMS:
ret = proc_free_streams(ps, p);
break;
+ case USBDEVFS_DROP_PRIVILEGES:
+ ret = proc_drop_privileges(ps, p);
+ break;
}
done:
diff --git a/include/uapi/linux/usbdevice_fs.h b/include/uapi/linux/usbdevice_fs.h
index ecbd176..a8653a6 100644
--- a/include/uapi/linux/usbdevice_fs.h
+++ b/include/uapi/linux/usbdevice_fs.h
@@ -135,6 +135,7 @@ struct usbdevfs_hub_portinfo {
#define USBDEVFS_CAP_BULK_SCATTER_GATHER 0x08
#define USBDEVFS_CAP_REAP_AFTER_DISCONNECT 0x10
#define USBDEVFS_CAP_MMAP 0x20
+#define USBDEVFS_CAP_DROP_PRIVILEGES 0x40
/* USBDEVFS_DISCONNECT_CLAIM flags & struct */
@@ -188,5 +189,6 @@ struct usbdevfs_streams {
#define USBDEVFS_DISCONNECT_CLAIM _IOR('U', 27, struct usbdevfs_disconnect_claim)
#define USBDEVFS_ALLOC_STREAMS _IOR('U', 28, struct usbdevfs_streams)
#define USBDEVFS_FREE_STREAMS _IOR('U', 29, struct usbdevfs_streams)
+#define USBDEVFS_DROP_PRIVILEGES _IOW('U', 30, __u32)
#endif /* _UAPI_LINUX_USBDEVICE_FS_H */
--
2.5.0
--
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