Re: [PATCH] Make /proc/net a symlink on /proc/self/net (v2)

[Stephen Smalley]

On Thu, 2008-03-06 at 19:45 +0300, Pavel Emelyanov wrote:
> Stephen Smalley wrote:
> > On Thu, 2008-03-06 at 12:18 +0300, Pavel Emelyanov wrote:
> >> Current /proc/net is done with so called "shadows", but current
> >> implementation is broken and has little chances to get fixed.
> >>
> >> The problem is that dentries subtree of /proc/net directory has
> >> fancy revalidation rules to make processes living in different
> >> net namespaces see different entries in /proc/net subtree, but
> >> currently, tasks see in the /proc/net subdir the contents of any
> >> other namespace, depending on who opened the file first.
> >>
> >> The proposed fix is to turn /proc/net into a symlink, which points
> >> to /proc/self/net, which in turn shows what previously was in
> >> /proc/net - the network-related info, from the net namespace the
> >> appropriate task lives in.
> >>
> >> # ls -l /proc/net
> >> lrwxrwxrwx  1 root root 8 Mar  5 15:17 /proc/net -> self/net
> >>
> >> In other words - this behaves like /proc/mounts, but unlike
> >> "mounts", "net" is not a file, but a directory.
> >>
> >> Fixed a task_struct leak in get_proc_task_net, pointed out by Paul.
> > 
> > Does this break SELinux labeling of /proc/net inodes and thus its access
> > controls on them?
> 
> It should not, since the proc_dir_etries are still organized in
> a required hierarchy.

Unfortunately, it does break selinux labeling of /proc/net inodes.
Easily seen by running ls -ZR /proc/net before and after the patch is
applied and comparing the results.  

Also, as a separate issue, a "find /proc/self/net ..." will show that
the hard link count is wrong for it.

Currently the inodes get labeled by selinux_proc_get_sid() by walking up
the proc_dir_entry tree to generate a name and prefix matching that name
in policy.  Before the patch, we'd get names like "//net/tcp", i.e.
relative to the root of proc (the extra leading slash is due to the
earlier proc net rewrite which also broke selinux until we adjusted it
to ignore it).  After the patch, we just get "//tcp", which is ambiguous
since we would also get that for a /proc/tcp inode if one existed.

Not trying to obstruct your proc net improvements, but just want to make
sure that selinux doesn't get broken in the process.

> 
> >> Signed-off-by: Pavel Emelyanov <xemul@xxxxxxxxxx>
> >>
> >> ---
> >>
> >> diff --git a/fs/proc/base.c b/fs/proc/base.c
> >> index 96ee899..cc43cf0 100644
> >> --- a/fs/proc/base.c
> >> +++ b/fs/proc/base.c
> >> @@ -2274,6 +2274,7 @@ static const struct pid_entry tgid_base_stuff[] = {
> >>  	DIR("task",       S_IRUGO|S_IXUGO, task),
> >>  	DIR("fd",         S_IRUSR|S_IXUSR, fd),
> >>  	DIR("fdinfo",     S_IRUSR|S_IXUSR, fdinfo),
> >> +	DIR("net",        S_IRUGO|S_IXUSR, net),
> >>  	REG("environ",    S_IRUSR, environ),
> >>  	INF("auxv",       S_IRUSR, pid_auxv),
> >>  	ONE("status",     S_IRUGO, pid_status),
> >> diff --git a/fs/proc/generic.c b/fs/proc/generic.c
> >> index 68971e6..a36ad3c 100644
> >> --- a/fs/proc/generic.c
> >> +++ b/fs/proc/generic.c
> >> @@ -377,15 +377,14 @@ static struct dentry_operations proc_dentry_operations =
> >>   * Don't create negative dentries here, return -ENOENT by hand
> >>   * instead.
> >>   */
> >> -struct dentry *proc_lookup(struct inode * dir, struct dentry *dentry, struct nameidata *nd)
> >> +struct dentry *proc_lookup_de(struct proc_dir_entry *de, struct inode *dir,
> >> +		struct dentry *dentry)
> >>  {
> >>  	struct inode *inode = NULL;
> >> -	struct proc_dir_entry * de;
> >>  	int error = -ENOENT;
> >>  
> >>  	lock_kernel();
> >>  	spin_lock(&proc_subdir_lock);
> >> -	de = PDE(dir);
> >>  	if (de) {
> >>  		for (de = de->subdir; de ; de = de->next) {
> >>  			if (de->namelen != dentry->d_name.len)
> >> @@ -393,8 +392,6 @@ struct dentry *proc_lookup(struct inode * dir, struct dentry *dentry, struct nam
> >>  			if (!memcmp(dentry->d_name.name, de->name, de->namelen)) {
> >>  				unsigned int ino;
> >>  
> >> -				if (de->shadow_proc)
> >> -					de = de->shadow_proc(current, de);
> >>  				ino = de->low_ino;
> >>  				de_get(de);
> >>  				spin_unlock(&proc_subdir_lock);
> >> @@ -417,6 +414,12 @@ out_unlock:
> >>  	return ERR_PTR(error);
> >>  }
> >>  
> >> +struct dentry *proc_lookup(struct inode *dir, struct dentry *dentry,
> >> +		struct nameidata *nd)
> >> +{
> >> +	return proc_lookup_de(PDE(dir), dir, dentry);
> >> +}
> >> +
> >>  /*
> >>   * This returns non-zero if at EOF, so that the /proc
> >>   * root directory can use this and check if it should
> >> @@ -426,10 +429,9 @@ out_unlock:
> >>   * value of the readdir() call, as long as it's non-negative
> >>   * for success..
> >>   */
> >> -int proc_readdir(struct file * filp,
> >> -	void * dirent, filldir_t filldir)
> >> +int proc_readdir_de(struct proc_dir_entry *de, struct file *filp, void *dirent,
> >> +		filldir_t filldir)
> >>  {
> >> -	struct proc_dir_entry * de;
> >>  	unsigned int ino;
> >>  	int i;
> >>  	struct inode *inode = filp->f_path.dentry->d_inode;
> >> @@ -438,7 +440,6 @@ int proc_readdir(struct file * filp,
> >>  	lock_kernel();
> >>  
> >>  	ino = inode->i_ino;
> >> -	de = PDE(inode);
> >>  	if (!de) {
> >>  		ret = -EINVAL;
> >>  		goto out;
> >> @@ -499,6 +500,13 @@ out:	unlock_kernel();
> >>  	return ret;	
> >>  }
> >>  
> >> +int proc_readdir(struct file *filp, void *dirent, filldir_t filldir)
> >> +{
> >> +	struct inode *inode = filp->f_path.dentry->d_inode;
> >> +
> >> +	return proc_readdir_de(PDE(inode), filp, dirent, filldir);
> >> +}
> >> +
> >>  /*
> >>   * These are the generic /proc directory operations. They
> >>   * use the in-memory "struct proc_dir_entry" tree to parse
> >> diff --git a/fs/proc/internal.h b/fs/proc/internal.h
> >> index 1c81c8f..bc72f5c 100644
> >> --- a/fs/proc/internal.h
> >> +++ b/fs/proc/internal.h
> >> @@ -64,6 +64,8 @@ extern const struct file_operations proc_numa_maps_operations;
> >>  extern const struct file_operations proc_smaps_operations;
> >>  extern const struct file_operations proc_clear_refs_operations;
> >>  extern const struct file_operations proc_pagemap_operations;
> >> +extern const struct file_operations proc_net_operations;
> >> +extern const struct inode_operations proc_net_inode_operations;
> >>  
> >>  void free_proc_entry(struct proc_dir_entry *de);
> >>  
> >> @@ -83,3 +85,8 @@ static inline int proc_fd(struct inode *inode)
> >>  {
> >>  	return PROC_I(inode)->fd;
> >>  }
> >> +
> >> +struct dentry *proc_lookup_de(struct proc_dir_entry *de, struct inode *ino,
> >> +		struct dentry *dentry);
> >> +int proc_readdir_de(struct proc_dir_entry *de, struct file *filp, void *dirent,
> >> +		filldir_t filldir);
> >> diff --git a/fs/proc/proc_net.c b/fs/proc/proc_net.c
> >> index 14e9b5a..18d413c 100644
> >> --- a/fs/proc/proc_net.c
> >> +++ b/fs/proc/proc_net.c
> >> @@ -63,6 +63,63 @@ int seq_release_net(struct inode *ino, struct file *f)
> >>  }
> >>  EXPORT_SYMBOL_GPL(seq_release_net);
> >>  
> >> +static struct net *get_proc_task_net(struct inode *dir)
> >> +{
> >> +	struct task_struct *task;
> >> +	struct nsproxy *ns;
> >> +	struct net *net = NULL;
> >> +
> >> +	rcu_read_lock();
> >> +	task = pid_task(proc_pid(dir), PIDTYPE_PID);
> >> +	if (task != NULL) {
> >> +		ns = task_nsproxy(task);
> >> +		if (ns != NULL)
> >> +			net = get_net(ns->net_ns);
> >> +	}
> >> +	rcu_read_unlock();
> >> +
> >> +	return net;
> >> +}
> >> +
> >> +static struct dentry *proc_tgid_net_lookup(struct inode *dir,
> >> +		struct dentry *dentry, struct nameidata *nd)
> >> +{
> >> +	struct dentry *de;
> >> +	struct net *net;
> >> +
> >> +	de = ERR_PTR(-ENOENT);
> >> +	net = get_proc_task_net(dir);
> >> +	if (net != NULL) {
> >> +		de = proc_lookup_de(net->proc_net, dir, dentry);
> >> +		put_net(net);
> >> +	}
> >> +	return de;
> >> +}
> >> +
> >> +const struct inode_operations proc_net_inode_operations = {
> >> +	.lookup		= proc_tgid_net_lookup,
> >> +};
> >> +
> >> +static int proc_tgid_net_readdir(struct file *filp, void *dirent,
> >> +		filldir_t filldir)
> >> +{
> >> +	int ret;
> >> +	struct net *net;
> >> +
> >> +	ret = -EINVAL;
> >> +	net = get_proc_task_net(filp->f_path.dentry->d_inode);
> >> +	if (net != NULL) {
> >> +		ret = proc_readdir_de(net->proc_net, filp, dirent, filldir);
> >> +		put_net(net);
> >> +	}
> >> +	return ret;
> >> +}
> >> +
> >> +const struct file_operations proc_net_operations = {
> >> +	.read		= generic_read_dir,
> >> +	.readdir	= proc_tgid_net_readdir,
> >> +};
> >> +
> >>  
> >>  struct proc_dir_entry *proc_net_fops_create(struct net *net,
> >>  	const char *name, mode_t mode, const struct file_operations *fops)
> >> @@ -83,14 +140,6 @@ struct net *get_proc_net(const struct inode *inode)
> >>  }
> >>  EXPORT_SYMBOL_GPL(get_proc_net);
> >>  
> >> -static struct proc_dir_entry *shadow_pde;
> >> -
> >> -static struct proc_dir_entry *proc_net_shadow(struct task_struct *task,
> >> -						struct proc_dir_entry *de)
> >> -{
> >> -	return task->nsproxy->net_ns->proc_net;
> >> -}
> >> -
> >>  struct proc_dir_entry *proc_net_mkdir(struct net *net, const char *name,
> >>  		struct proc_dir_entry *parent)
> >>  {
> >> @@ -104,45 +153,35 @@ EXPORT_SYMBOL_GPL(proc_net_mkdir);
> >>  
> >>  static __net_init int proc_net_ns_init(struct net *net)
> >>  {
> >> -	struct proc_dir_entry *root, *netd, *net_statd;
> >> +	struct proc_dir_entry *netd, *net_statd;
> >>  	int err;
> >>  
> >>  	err = -ENOMEM;
> >> -	root = kzalloc(sizeof(*root), GFP_KERNEL);
> >> -	if (!root)
> >> +	netd = kzalloc(sizeof(*netd), GFP_KERNEL);
> >> +	if (!netd)
> >>  		goto out;
> >>  
> >> -	err = -EEXIST;
> >> -	netd = proc_net_mkdir(net, "net", root);
> >> -	if (!netd)
> >> -		goto free_root;
> >> +	netd->data = net;
> >>  
> >>  	err = -EEXIST;
> >>  	net_statd = proc_net_mkdir(net, "stat", netd);
> >>  	if (!net_statd)
> >>  		goto free_net;
> >>  
> >> -	root->data = net;
> >> -
> >> -	net->proc_net_root = root;
> >>  	net->proc_net = netd;
> >>  	net->proc_net_stat = net_statd;
> >> -	err = 0;
> >> +	return 0;
> >>  
> >> +free_net:
> >> +	kfree(netd);
> >>  out:
> >>  	return err;
> >> -free_net:
> >> -	remove_proc_entry("net", root);
> >> -free_root:
> >> -	kfree(root);
> >> -	goto out;
> >>  }
> >>  
> >>  static __net_exit void proc_net_ns_exit(struct net *net)
> >>  {
> >>  	remove_proc_entry("stat", net->proc_net);
> >> -	remove_proc_entry("net", net->proc_net_root);
> >> -	kfree(net->proc_net_root);
> >> +	kfree(net->proc_net);
> >>  }
> >>  
> >>  static struct pernet_operations __net_initdata proc_net_ns_ops = {
> >> @@ -152,8 +191,7 @@ static struct pernet_operations __net_initdata proc_net_ns_ops = {
> >>  
> >>  int __init proc_net_init(void)
> >>  {
> >> -	shadow_pde = proc_mkdir("net", NULL);
> >> -	shadow_pde->shadow_proc = proc_net_shadow;
> >> +	proc_symlink("net", NULL, "self/net");
> >>  
> >>  	return register_pernet_subsys(&proc_net_ns_ops);
> >>  }
> >> diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
> >> index d9a9e71..9b6c935 100644
> >> --- a/include/linux/proc_fs.h
> >> +++ b/include/linux/proc_fs.h
> >> @@ -50,8 +50,6 @@ typedef	int (read_proc_t)(char *page, char **start, off_t off,
> >>  typedef	int (write_proc_t)(struct file *file, const char __user *buffer,
> >>  			   unsigned long count, void *data);
> >>  typedef int (get_info_t)(char *, char **, off_t, int);
> >> -typedef struct proc_dir_entry *(shadow_proc_t)(struct task_struct *task,
> >> -						struct proc_dir_entry *pde);
> >>  
> >>  struct proc_dir_entry {
> >>  	unsigned int low_ino;
> >> @@ -82,7 +80,6 @@ struct proc_dir_entry {
> >>  	int pde_users;	/* number of callers into module in progress */
> >>  	spinlock_t pde_unload_lock; /* proc_fops checks and pde_users bumps */
> >>  	struct completion *pde_unload_completion;
> >> -	shadow_proc_t *shadow_proc;
> >>  };
> >>  
> >>  struct kcore_list {
> >> diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
> >> index 28738b7..923f2b8 100644
> >> --- a/include/net/net_namespace.h
> >> +++ b/include/net/net_namespace.h
> >> @@ -31,7 +31,6 @@ struct net {
> >>  
> >>  	struct proc_dir_entry 	*proc_net;
> >>  	struct proc_dir_entry 	*proc_net_stat;
> >> -	struct proc_dir_entry 	*proc_net_root;
> >>  
> >>  	struct list_head	sysctl_table_headers;
> >>  
> >> --
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> >> the body of a message to majordomo@xxxxxxxxxxxxxxx
> >> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> >> Please read the FAQ at  http://www.tux.org/lkml/
-- 
Stephen Smalley
National Security Agency

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