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Date: Thu, 06 Mar 2008 11:25:35 +0300
From: Pavel Emelyanov <xemul@...nvz.org>
To: paulmck@...ux.vnet.ibm.com
CC: Andrew Morton <akpm@...ux-foundation.org>,
David Miller <davem@...emloft.net>,
Linux Netdev List <netdev@...r.kernel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
"Eric W. Biederman" <ebiederm@...ssion.com>,
Alexey Dobriyan <adobriyan@...nvz.org>
Subject: Re: [PATCH] Make /proc/net a symlink on /proc/self/net
Paul E. McKenney wrote:
> On Wed, Mar 05, 2008 at 03:20:07PM +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.
>
> One question below for get_proc_task_net() -- I don't see how the
> reference to a task struct is released.
Shame on me :( Thanks Paul, I'll prepare the fixed patch shortly,
all the more so Eric finally agreed with it...
> Thanx, Paul
>
>> Signed-off-by: Pavel Emelyanov <xemul@...nvz.org>
>>
>> ---
>>
>> 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..3372c2e 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 = get_proc_task(dir);
>
> This implies a get_task_struct(), as get_proc_task() invokes get_proc_task()
> which invokes get_pid_task() which invokes get_task_struct().
>
> I don't see the corresponding put_task_struct() -- what am I missing here?
>
>> + 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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>
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