Re: [PATCH v3 02/11] lsm: /proc/$PID/attr/label_map file and getprocattr_seq hook

["Serge E. Hallyn" <serge@hallyn.com>]

On Fri, Jul 24, 2015 at 12:04:36PM +0200, Lukasz Pawelczyk wrote:
> This commit adds a new proc attribute, label_map that is required by an
> upcoming Smack namespace. In general it can be used to hold a map of
> labels, e.g. to be used in namespaces.
> 
> Due to the nature of this file, the standard getprocattr hook might not
> be enough to handle it. The map's output can in principle be greater
> than page size to which the aforementioned hook is limited.
> To handle this properly a getprocattr_seq LSM hook has been added that
> makes it possible to handle any chosen proc attr by seq operations.
> 
> See the documentation in the patch below for the details about how to
> use the hook.
> 
> Signed-off-by: Lukasz Pawelczyk <l.pawelczyk@samsung.com>

Acked-by: Serge Hallyn <serge.hallyn@canonical.com>

> ---
>  fs/proc/base.c            | 81 +++++++++++++++++++++++++++++++++++++++++++----
>  include/linux/lsm_hooks.h | 15 +++++++++
>  include/linux/security.h  |  9 ++++++
>  security/security.c       |  8 +++++
>  4 files changed, 107 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index aa50d1a..e5ac827 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -2338,20 +2338,77 @@ out:
>  }
>  
>  #ifdef CONFIG_SECURITY
> +static int proc_pid_attr_open(struct inode *inode, struct file *file)
> +{
> +	const char *name = file->f_path.dentry->d_name.name;
> +	const struct seq_operations *ops;
> +	struct task_struct *task;
> +	struct seq_file *seq;
> +	int ret;
> +
> +	file->private_data = NULL;
> +
> +	task = get_proc_task(inode);
> +	if (!task)
> +		return -ESRCH;
> +
> +	/* don't use seq_ops if they are not provided by LSM */
> +	ret = security_getprocattr_seq(task, name, &ops);
> +	if (ret == -EOPNOTSUPP) {
> +		put_task_struct(task);
> +		return 0;
> +	}
> +	if (ret) {
> +		put_task_struct(task);
> +		return ret;
> +	}
> +
> +	ret = seq_open(file, ops);
> +	if (ret) {
> +		put_task_struct(task);
> +		return ret;
> +	}
> +
> +	seq = file->private_data;
> +	seq->private = task;
> +
> +	return 0;
> +}
> +
> +static int proc_pid_attr_release(struct inode *inode, struct file *file)
> +{
> +	struct seq_file *seq;
> +	struct task_struct *task;
> +
> +	/* don't use seq_ops if they were not provided by LSM */
> +	if (file->private_data == NULL)
> +		return 0;
> +
> +	seq = file->private_data;
> +	task = seq->private;
> +	put_task_struct(task);
> +
> +	return seq_release(inode, file);
> +}
> +
>  static ssize_t proc_pid_attr_read(struct file * file, char __user * buf,
>  				  size_t count, loff_t *ppos)
>  {
> -	struct inode * inode = file_inode(file);
> +	struct inode *inode = file_inode(file);
> +	const char *name = file->f_path.dentry->d_name.name;
>  	char *p = NULL;
>  	ssize_t length;
> -	struct task_struct *task = get_proc_task(inode);
> +	struct task_struct *task;
> +
> +	/* use seq_ops if they were provided by LSM */
> +	if (file->private_data)
> +		return seq_read(file, buf, count, ppos);
>  
> +	task = get_proc_task(inode);
>  	if (!task)
>  		return -ESRCH;
>  
> -	length = security_getprocattr(task,
> -				      (char*)file->f_path.dentry->d_name.name,
> -				      &p);
> +	length = security_getprocattr(task, (char *)name, &p);
>  	put_task_struct(task);
>  	if (length > 0)
>  		length = simple_read_from_buffer(buf, count, ppos, p, length);
> @@ -2359,6 +2416,15 @@ static ssize_t proc_pid_attr_read(struct file * file, char __user * buf,
>  	return length;
>  }
>  
> +static loff_t proc_pid_attr_lseek(struct file *file, loff_t offset, int whence)
> +{
> +	/* use seq_ops if they were provided by LSM */
> +	if (file->private_data)
> +		return seq_lseek(file, offset, whence);
> +
> +	return generic_file_llseek(file, offset, whence);
> +}
> +
>  static ssize_t proc_pid_attr_write(struct file * file, const char __user * buf,
>  				   size_t count, loff_t *ppos)
>  {
> @@ -2405,9 +2471,11 @@ out_no_task:
>  }
>  
>  static const struct file_operations proc_pid_attr_operations = {
> +	.open		= proc_pid_attr_open,
> +	.release	= proc_pid_attr_release,
>  	.read		= proc_pid_attr_read,
> +	.llseek		= proc_pid_attr_lseek,
>  	.write		= proc_pid_attr_write,
> -	.llseek		= generic_file_llseek,
>  };
>  
>  static const struct pid_entry attr_dir_stuff[] = {
> @@ -2417,6 +2485,7 @@ static const struct pid_entry attr_dir_stuff[] = {
>  	REG("fscreate",   S_IRUGO|S_IWUGO, proc_pid_attr_operations),
>  	REG("keycreate",  S_IRUGO|S_IWUGO, proc_pid_attr_operations),
>  	REG("sockcreate", S_IRUGO|S_IWUGO, proc_pid_attr_operations),
> +	REG("label_map",  S_IRUGO|S_IWUGO, proc_pid_attr_operations),
>  };
>  
>  static int proc_attr_dir_readdir(struct file *file, struct dir_context *ctx)
> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> index 228558c..d347e66 100644
> --- a/include/linux/lsm_hooks.h
> +++ b/include/linux/lsm_hooks.h
> @@ -1208,6 +1208,18 @@
>   *	@name full extended attribute name to check against
>   *	LSM as a MAC label.
>   *
> + * @getprocattr_seq:
> + *	An alternative to the getprocattr, that makes it possible for an attr
> + *	file to be handled by seq operations. If this function returns valid
> + *	@ops for a specific @name, those operations will be used and
> + *	getprocattr will not be called.
> + *	A proper task for the file is then passed in seq_file->private.
> + *	@p a task associated with the proc file.
> + *	@name name of the attr file under /proc/$PID/attr/ to be handled.
> + *	@ops (out) seq_operations to be used for @name.
> + *	Return 0 if @name is to be handled by seq, EOPNOTSUPP if getprocattr()
> + *	should be used. Other errors will be passed to user-space.
> + *
>   * @secid_to_secctx:
>   *	Convert secid to security context.  If secdata is NULL the length of
>   *	the result will be returned in seclen, but no secdata will be returned.
> @@ -1525,6 +1537,8 @@ union security_list_options {
>  
>  	void (*d_instantiate)(struct dentry *dentry, struct inode *inode);
>  
> +	int (*getprocattr_seq)(struct task_struct *p, const char *name,
> +			       const struct seq_operations **ops);
>  	int (*getprocattr)(struct task_struct *p, char *name, char **value);
>  	int (*setprocattr)(struct task_struct *p, char *name, void *value,
>  				size_t size);
> @@ -1774,6 +1788,7 @@ struct security_hook_heads {
>  	struct list_head sem_semop;
>  	struct list_head netlink_send;
>  	struct list_head d_instantiate;
> +	struct list_head getprocattr_seq;
>  	struct list_head getprocattr;
>  	struct list_head setprocattr;
>  	struct list_head ismaclabel;
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 1b0eccc..3090bb2 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -345,6 +345,8 @@ int security_sem_semctl(struct sem_array *sma, int cmd);
>  int security_sem_semop(struct sem_array *sma, struct sembuf *sops,
>  			unsigned nsops, int alter);
>  void security_d_instantiate(struct dentry *dentry, struct inode *inode);
> +int security_getprocattr_seq(struct task_struct *p, const char *name,
> +			     const struct seq_operations **ops);
>  int security_getprocattr(struct task_struct *p, char *name, char **value);
>  int security_setprocattr(struct task_struct *p, char *name, void *value, size_t size);
>  int security_netlink_send(struct sock *sk, struct sk_buff *skb);
> @@ -1057,6 +1059,13 @@ static inline int security_sem_semop(struct sem_array *sma,
>  static inline void security_d_instantiate(struct dentry *dentry, struct inode *inode)
>  { }
>  
> +static inline int security_getprocattr_seq(struct task_struct *p,
> +					   const char *name,
> +					   const struct seq_operations **ops)
> +{
> +	return -EOPNOTSUPP;
> +}
> +
>  static inline int security_getprocattr(struct task_struct *p, char *name, char **value)
>  {
>  	return -EINVAL;
> diff --git a/security/security.c b/security/security.c
> index 5e66388..e348e38 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -1126,6 +1126,12 @@ void security_d_instantiate(struct dentry *dentry, struct inode *inode)
>  }
>  EXPORT_SYMBOL(security_d_instantiate);
>  
> +int security_getprocattr_seq(struct task_struct *p, const char *name,
> +			     const struct seq_operations **ops)
> +{
> +	return call_int_hook(getprocattr_seq, -EOPNOTSUPP, p, name, ops);
> +}
> +
>  int security_getprocattr(struct task_struct *p, char *name, char **value)
>  {
>  	return call_int_hook(getprocattr, -EINVAL, p, name, value);
> @@ -1778,6 +1784,8 @@ struct security_hook_heads security_hook_heads = {
>  	.netlink_send =	LIST_HEAD_INIT(security_hook_heads.netlink_send),
>  	.d_instantiate =
>  		LIST_HEAD_INIT(security_hook_heads.d_instantiate),
> +	.getprocattr_seq =
> +		LIST_HEAD_INIT(security_hook_heads.getprocattr_seq),
>  	.getprocattr =	LIST_HEAD_INIT(security_hook_heads.getprocattr),
>  	.setprocattr =	LIST_HEAD_INIT(security_hook_heads.setprocattr),
>  	.ismaclabel =	LIST_HEAD_INIT(security_hook_heads.ismaclabel),
> -- 
> 2.4.3