Re: [PATCH] driver core: add uid and gid to devtmpfs

[Eric W. Biederman]

Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> writes:

> From: Kay Sievers <kay@xxxxxxxx>
>
> Some drivers want to tell userspace what uid and gid should be used for
> their device nodes, so allow that information to percolate through the
> driver core to userspace in order to make this happen.  This means that
> some systems (i.e.  Android and friends) will not need to even run a
> udev-like daemon for their device node manager and can just rely in
> devtmpfs fully, reducing their footprint even more.

This patch is really badly broken in it's uid and gid handling.
Nearly every line of this patch is wrong.

uids and gids in the kernel need to be stored in kuid_t's and kgid_t's.

> Signed-off-by: Kay Sievers <kay@xxxxxxxx>
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> ---
>  block/genhd.c           |    3 ++-
>  drivers/base/core.c     |   17 +++++++++++++----
>  drivers/base/devtmpfs.c |   27 +++++++++++++++++----------
>  drivers/usb/core/usb.c  |    3 ++-
>  include/linux/device.h  |    7 +++++--
>  5 files changed, 39 insertions(+), 18 deletions(-)
>
> --- a/block/genhd.c
> +++ b/block/genhd.c
> @@ -1111,7 +1111,8 @@ struct class block_class = {
>  	.name		= "block",
>  };
>  
> -static char *block_devnode(struct device *dev, umode_t *mode)
> +static char *block_devnode(struct device *dev, umode_t *mode,
> +			   uid_t *uid, gid_t *gid)
This needs be kuid_t and kgid_t.

>  {
>  	struct gendisk *disk = dev_to_disk(dev);
>  
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -283,15 +283,21 @@ static int dev_uevent(struct kset *kset,
>  		const char *tmp;
>  		const char *name;
>  		umode_t mode = 0;
> +		uid_t uid = 0;
> +		gid_t gid = 0;
This needs to be:
		kuid_t uid = GLOBAL_ROOT_UID;
		kgid_t gid = GLOBAL_ROOT_GID;

>  		add_uevent_var(env, "MAJOR=%u", MAJOR(dev->devt));
>  		add_uevent_var(env, "MINOR=%u", MINOR(dev->devt));
> -		name = device_get_devnode(dev, &mode, &tmp);
> +		name = device_get_devnode(dev, &mode, &uid, &gid, &tmp);
>  		if (name) {
>  			add_uevent_var(env, "DEVNAME=%s", name);
> -			kfree(tmp);
>  			if (mode)
>  				add_uevent_var(env, "DEVMODE=%#o", mode & 0777);
> +			if (uid)
> +				add_uevent_var(env, "DEVUID=%u", uid);
> +			if (gid)
> +				add_uevent_var(env, "DEVGID=%u", gid);

Which user namespace are your users in?
At the very least this should be:
+			if (!uid_eq(uid, GLOBAL_ROOT_UID)
+				add_uevent_var(env, "DEVUID=%u", from_kuid(&init_user_ns, uid));
+			if (!gid_eq(gid, GLOBAL_ROOT_GID))
+				add_uevent_var(env, "DEVGID=%u", from_kgid(&init_user_ns, gid));

I suppose you can assume your users are in the initial user namespace,
as mknod won't work in any other user namespace.

Still it approaches being twisted to have files like
/sys/class/net/eth0/uevent that anyone can read that will only return
values in the initial user namespace.

> +			kfree(tmp);
>  		}
>  	}
>  
> @@ -1274,6 +1280,8 @@ static struct device *next_device(struct
>   * device_get_devnode - path of device node file
>   * @dev: device
>   * @mode: returned file access mode
> + * @uid: returned file owner
> + * @gid: returned file group
>   * @tmp: possibly allocated string
>   *
>   * Return the relative path of a possible device node.
> @@ -1282,7 +1290,8 @@ static struct device *next_device(struct
>   * freed by the caller.
>   */
>  const char *device_get_devnode(struct device *dev,
> -			       umode_t *mode, const char **tmp)
> +			       umode_t *mode, uid_t *uid, gid_t *gid,
> +			       const char **tmp)

This needs to be kuid_t and kgid_t
>  {
>  	char *s;
>  
> @@ -1290,7 +1299,7 @@ const char *device_get_devnode(struct de
>  
>  	/* the device type may provide a specific name */
>  	if (dev->type && dev->type->devnode)
> -		*tmp = dev->type->devnode(dev, mode);
> +		*tmp = dev->type->devnode(dev, mode, uid, gid);
>  	if (*tmp)
>  		return *tmp;
>  
> --- a/drivers/base/devtmpfs.c
> +++ b/drivers/base/devtmpfs.c
> @@ -41,6 +41,8 @@ static struct req {
>  	int err;
>  	const char *name;
>  	umode_t mode;	/* 0 => delete */
> +	uid_t uid;
> +	gid_t gid;

This needs to be kuid_t and kgid_t.
>  	struct device *dev;
>  } *requests;
>  
> @@ -85,7 +87,9 @@ int devtmpfs_create_node(struct device *
>  		return 0;
>  
>  	req.mode = 0;
> -	req.name = device_get_devnode(dev, &req.mode, &tmp);
> +	req.uid = 0;
> +	req.gid = 0;
This needs to be.
req.uid = GLOBAL_ROOT_UID;
req.gid = GLOBAL_ROOT_GID;
> +	req.name = device_get_devnode(dev, &req.mode, &req.uid, &req.gid, &tmp);
>  	if (!req.name)
>  		return -ENOMEM;
>  
> @@ -121,7 +125,7 @@ int devtmpfs_delete_node(struct device *
>  	if (!thread)
>  		return 0;
>  
> -	req.name = device_get_devnode(dev, NULL, &tmp);
> +	req.name = device_get_devnode(dev, NULL, NULL, NULL, &tmp);
>  	if (!req.name)
>  		return -ENOMEM;
>  
> @@ -187,7 +191,8 @@ static int create_path(const char *nodep
>  	return err;
>  }
>  
> -static int handle_create(const char *nodename, umode_t mode, struct device *dev)
> +static int handle_create(const char *nodename, umode_t mode, uid_t uid,
> +			 gid_t gid, struct device *dev)
This needs tobe kuid_t and kgid_t.
>  {
>  	struct dentry *dentry;
>  	struct path path;
> @@ -201,14 +206,14 @@ static int handle_create(const char *nod
>  	if (IS_ERR(dentry))
>  		return PTR_ERR(dentry);
>  
> -	err = vfs_mknod(path.dentry->d_inode,
> -			dentry, mode, dev->devt);
> +	err = vfs_mknod(path.dentry->d_inode, dentry, mode, dev->devt);
Why this gratuitious change?
>  	if (!err) {
>  		struct iattr newattrs;
>  
> -		/* fixup possibly umasked mode */
>  		newattrs.ia_mode = mode;
> -		newattrs.ia_valid = ATTR_MODE;
> +		newattrs.ia_uid = uid;
> +		newattrs.ia_gid = gid;
This doesn't even compile because the types are wrong.
> +		newattrs.ia_valid = ATTR_MODE|ATTR_UID|ATTR_GID;
>  		mutex_lock(&dentry->d_inode->i_mutex);
>  		notify_change(dentry, &newattrs);
>  		mutex_unlock(&dentry->d_inode->i_mutex);
> @@ -358,10 +363,11 @@ int devtmpfs_mount(const char *mntdir)
>  
>  static DECLARE_COMPLETION(setup_done);
>  
> -static int handle(const char *name, umode_t mode, struct device *dev)
> +static int handle(const char *name, umode_t mode, uid_t uid, gid_t gid,
The types are wrong here.
> +		  struct device *dev)
>  {
>  	if (mode)
> -		return handle_create(name, mode, dev);
> +		return handle_create(name, mode, uid, gid, dev);
>  	else
>  		return handle_remove(name, dev);
>  }
> @@ -387,7 +393,8 @@ static int devtmpfsd(void *p)
>  			spin_unlock(&req_lock);
>  			while (req) {
>  				struct req *next = req->next;
> -				req->err = handle(req->name, req->mode, req->dev);
> +				req->err = handle(req->name, req->mode,
> +						  req->uid, req->gid, req->dev);
>  				complete(&req->done);
>  				req = next;
>  			}
> --- a/drivers/usb/core/usb.c
> +++ b/drivers/usb/core/usb.c
> @@ -317,7 +317,8 @@ static const struct dev_pm_ops usb_devic
>  #endif	/* CONFIG_PM */
>  
>  
> -static char *usb_devnode(struct device *dev, umode_t *mode)
> +static char *usb_devnode(struct device *dev,
> +			 umode_t *mode, uid_t *uid, gid_t *gid)
The types are again wrong here.
>  {
>  	struct usb_device *usb_dev;
>  
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -25,6 +25,7 @@
>  #include <linux/pm.h>
>  #include <linux/atomic.h>
>  #include <linux/ratelimit.h>
> +#include <linux/uidgid.h>
>  #include <asm/device.h>
>  
>  struct device;
> @@ -471,7 +472,8 @@ struct device_type {
>  	const char *name;
>  	const struct attribute_group **groups;
>  	int (*uevent)(struct device *dev, struct kobj_uevent_env *env);
> -	char *(*devnode)(struct device *dev, umode_t *mode);
> +	char *(*devnode)(struct device *dev, umode_t *mode,
> +			 uid_t *uid, gid_t *gid);
The types are wrong here.
>  	void (*release)(struct device *dev);
>  
>  	const struct dev_pm_ops *pm;
> @@ -849,7 +851,8 @@ extern int device_rename(struct device *
>  extern int device_move(struct device *dev, struct device *new_parent,
>  		       enum dpm_order dpm_order);
>  extern const char *device_get_devnode(struct device *dev,
> -				      umode_t *mode, const char **tmp);
> +				      umode_t *mode, uid_t *uid, gid_t *gid,
And the types are wrong here.
> +				      const char **tmp);
>  extern void *dev_get_drvdata(const struct device *dev);
>  extern int dev_set_drvdata(struct device *dev, void *data);
>  
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