[PATCH] sysctl: reimplement the sysctl proc support

With this change the sysctl inodes can be cached and nothing needs to be done
when removing a sysctl table.

For a cost of 2K code we will save about 4K of static tables (when we remove
de from ctl_table) and 70K in proc_dir_entries that we will not allocate, or
about half that on a 32bit arch.

The speed feels about the same, even though we can now cache the sysctl
dentries :(

We get the core advantage that we don't need to have a 1 to 1 mapping between
ctl table entries and proc files.  Making it possible to have /proc/sys vary
depending on the namespace you are in.  The currently merged namespaces don't
have an issue here but the network namespace under /proc/sys/net needs to have
different directories depending on which network adapters are visible.  By
simply being a cache different directories being visible depending on who you
are is trivial to implement.

[akpm@osdl.org: fix uninitialised var]
[akpm@osdl.org: fix ARM build]
[bunk@stusta.de: make things static]
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Cc: Russell King <rmk@arm.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 478 insertions, 0 deletions

diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
new file mode 100644
index 00000000000..bb16a1e7882
--- /dev/null
+++ b/fs/proc/proc_sysctl.c
@@ -0,0 +1,478 @@
+/*
+ * /proc/sys support
+ */
+
+#include <linux/sysctl.h>
+#include <linux/proc_fs.h>
+#include <linux/security.h>
+#include "internal.h"
+
+static struct dentry_operations proc_sys_dentry_operations;
+static const struct file_operations proc_sys_file_operations;
+static struct inode_operations proc_sys_inode_operations;
+
+static void proc_sys_refresh_inode(struct inode *inode, struct ctl_table *table)
+{
+	/* Refresh the cached information bits in the inode */
+	if (table) {
+		inode->i_uid = 0;
+		inode->i_gid = 0;
+		inode->i_mode = table->mode;
+		if (table->proc_handler) {
+			inode->i_mode |= S_IFREG;
+			inode->i_nlink = 1;
+		} else {
+			inode->i_mode |= S_IFDIR;
+			inode->i_nlink = 0;	/* It is too hard to figure out */
+		}
+	}
+}
+
+static struct inode *proc_sys_make_inode(struct inode *dir, struct ctl_table *table)
+{
+	struct inode *inode;
+	struct proc_inode *dir_ei, *ei;
+	int depth;
+
+	inode = new_inode(dir->i_sb);
+	if (!inode)
+		goto out;
+
+	/* A directory is always one deeper than it's parent */
+	dir_ei = PROC_I(dir);
+	depth = dir_ei->fd + 1;
+
+	ei = PROC_I(inode);
+	ei->fd = depth;
+	inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
+	inode->i_op = &proc_sys_inode_operations;
+	inode->i_fop = &proc_sys_file_operations;
+	proc_sys_refresh_inode(inode, table);
+out:
+	return inode;
+}
+
+static struct dentry *proc_sys_ancestor(struct dentry *dentry, int depth)
+{
+	for (;;) {
+		struct proc_inode *ei;
+
+		ei = PROC_I(dentry->d_inode);
+		if (ei->fd == depth)
+			break; /* found */
+
+		dentry = dentry->d_parent;
+	}
+	return dentry;
+}
+
+static struct ctl_table *proc_sys_lookup_table_one(struct ctl_table *table,
+							struct qstr *name)
+{
+	int len;
+	for ( ; table->ctl_name || table->procname; table++) {
+
+		if (!table->procname)
+			continue;
+
+		len = strlen(table->procname);
+		if (len != name->len)
+			continue;
+
+		if (memcmp(table->procname, name->name, len) != 0)
+			continue;
+
+		/* I have a match */
+		return table;
+	}
+	return NULL;
+}
+
+static struct ctl_table *proc_sys_lookup_table(struct dentry *dentry,
+						struct ctl_table *table)
+{
+	struct dentry *ancestor;
+	struct proc_inode *ei;
+	int depth, i;
+
+	ei = PROC_I(dentry->d_inode);
+	depth = ei->fd;
+
+	if (depth == 0)
+		return table;
+
+	for (i = 1; table && (i <= depth); i++) {
+		ancestor = proc_sys_ancestor(dentry, i);
+		table = proc_sys_lookup_table_one(table, &ancestor->d_name);
+		if (table)
+			table = table->child;
+	}
+	return table;
+
+}
+static struct ctl_table *proc_sys_lookup_entry(struct dentry *dparent,
+						struct qstr *name,
+						struct ctl_table *table)
+{
+	table = proc_sys_lookup_table(dparent, table);
+	if (table)
+		table = proc_sys_lookup_table_one(table, name);
+	return table;
+}
+
+static struct ctl_table *do_proc_sys_lookup(struct dentry *parent,
+						struct qstr *name,
+						struct ctl_table_header **ptr)
+{
+	struct ctl_table_header *head;
+	struct ctl_table *table = NULL;
+
+	for (head = sysctl_head_next(NULL); head;
+			head = sysctl_head_next(head)) {
+		table = proc_sys_lookup_entry(parent, name, head->ctl_table);
+		if (table)
+			break;
+	}
+	*ptr = head;
+	return table;
+}
+
+static struct dentry *proc_sys_lookup(struct inode *dir, struct dentry *dentry,
+					struct nameidata *nd)
+{
+	struct ctl_table_header *head;
+	struct inode *inode;
+	struct dentry *err;
+	struct ctl_table *table;
+
+	err = ERR_PTR(-ENOENT);
+	table = do_proc_sys_lookup(dentry->d_parent, &dentry->d_name, &head);
+	if (!table)
+		goto out;
+
+	err = ERR_PTR(-ENOMEM);
+	inode = proc_sys_make_inode(dir, table);
+	if (!inode)
+		goto out;
+
+	err = NULL;
+	dentry->d_op = &proc_sys_dentry_operations;
+	d_add(dentry, inode);
+
+out:
+	sysctl_head_finish(head);
+	return err;
+}
+
+static ssize_t proc_sys_read(struct file *filp, char __user *buf,
+				size_t count, loff_t *ppos)
+{
+	struct dentry *dentry = filp->f_dentry;
+	struct ctl_table_header *head;
+	struct ctl_table *table;
+	ssize_t error, res;
+
+	table = do_proc_sys_lookup(dentry->d_parent, &dentry->d_name, &head);
+	/* Has the sysctl entry disappeared on us? */
+	error = -ENOENT;
+	if (!table)
+		goto out;
+
+	/* Has the sysctl entry been replaced by a directory? */
+	error = -EISDIR;
+	if (!table->proc_handler)
+		goto out;
+
+	/*
+	 * At this point we know that the sysctl was not unregistered
+	 * and won't be until we finish.
+	 */
+	error = -EPERM;
+	if (sysctl_perm(table, MAY_READ))
+		goto out;
+
+	/* careful: calling conventions are nasty here */
+	res = count;
+	error = table->proc_handler(table, 0, filp, buf, &res, ppos);
+	if (!error)
+		error = res;
+out:
+	sysctl_head_finish(head);
+
+	return error;
+}
+
+static ssize_t proc_sys_write(struct file *filp, const char __user *buf,
+				size_t count, loff_t *ppos)
+{
+	struct dentry *dentry = filp->f_dentry;
+	struct ctl_table_header *head;
+	struct ctl_table *table;
+	ssize_t error, res;
+
+	table = do_proc_sys_lookup(dentry->d_parent, &dentry->d_name, &head);
+	/* Has the sysctl entry disappeared on us? */
+	error = -ENOENT;
+	if (!table)
+		goto out;
+
+	/* Has the sysctl entry been replaced by a directory? */
+	error = -EISDIR;
+	if (!table->proc_handler)
+		goto out;
+
+	/*
+	 * At this point we know that the sysctl was not unregistered
+	 * and won't be until we finish.
+	 */
+	error = -EPERM;
+	if (sysctl_perm(table, MAY_WRITE))
+		goto out;
+
+	/* careful: calling conventions are nasty here */
+	res = count;
+	error = table->proc_handler(table, 1, filp, (char __user *)buf,
+				    &res, ppos);
+	if (!error)
+		error = res;
+out:
+	sysctl_head_finish(head);
+
+	return error;
+}
+
+
+static int proc_sys_fill_cache(struct file *filp, void *dirent,
+				filldir_t filldir, struct ctl_table *table)
+{
+	struct ctl_table_header *head;
+	struct ctl_table *child_table = NULL;
+	struct dentry *child, *dir = filp->f_path.dentry;
+	struct inode *inode;
+	struct qstr qname;
+	ino_t ino = 0;
+	unsigned type = DT_UNKNOWN;
+	int ret;
+
+	qname.name = table->procname;
+	qname.len  = strlen(table->procname);
+	qname.hash = full_name_hash(qname.name, qname.len);
+
+	/* Suppress duplicates.
+	 * Only fill a directory entry if it is the value that
+	 * an ordinary lookup of that name returns.  Hide all
+	 * others.
+	 *
+	 * If we ever cache this translation in the dcache
+	 * I should do a dcache lookup first.  But for now
+	 * it is just simpler not to.
+	 */
+	ret = 0;
+	child_table = do_proc_sys_lookup(dir, &qname, &head);
+	sysctl_head_finish(head);
+	if (child_table != table)
+		return 0;
+
+	child = d_lookup(dir, &qname);
+	if (!child) {
+		struct dentry *new;
+		new = d_alloc(dir, &qname);
+		if (new) {
+			inode = proc_sys_make_inode(dir->d_inode, table);
+			if (!inode)
+				child = ERR_PTR(-ENOMEM);
+			else {
+				new->d_op = &proc_sys_dentry_operations;
+				d_add(new, inode);
+			}
+			if (child)
+				dput(new);
+			else
+				child = new;
+		}
+	}
+	if (!child || IS_ERR(child) || !child->d_inode)
+		goto end_instantiate;
+	inode = child->d_inode;
+	if (inode) {
+		ino  = inode->i_ino;
+		type = inode->i_mode >> 12;
+	}
+	dput(child);
+end_instantiate:
+	if (!ino)
+		ino= find_inode_number(dir, &qname);
+	if (!ino)
+		ino = 1;
+	return filldir(dirent, qname.name, qname.len, filp->f_pos, ino, type);
+}
+
+static int proc_sys_readdir(struct file *filp, void *dirent, filldir_t filldir)
+{
+	struct dentry *dentry = filp->f_dentry;
+	struct inode *inode = dentry->d_inode;
+	struct ctl_table_header *head = NULL;
+	struct ctl_table *table;
+	unsigned long pos;
+	int ret;
+
+	ret = -ENOTDIR;
+	if (!S_ISDIR(inode->i_mode))
+		goto out;
+
+	ret = 0;
+	/* Avoid a switch here: arm builds fail with missing __cmpdi2 */
+	if (filp->f_pos == 0) {
+		if (filldir(dirent, ".", 1, filp->f_pos,
+				inode->i_ino, DT_DIR) < 0)
+			goto out;
+		filp->f_pos++;
+	}
+	if (filp->f_pos == 1) {
+		if (filldir(dirent, "..", 2, filp->f_pos,
+				parent_ino(dentry), DT_DIR) < 0)
+			goto out;
+		filp->f_pos++;
+	}
+	pos = 2;
+
+	/* - Find each instance of the directory
+	 * - Read all entries in each instance
+	 * - Before returning an entry to user space lookup the entry
+	 *   by name and if I find a different entry don't return
+	 *   this one because it means it is a buried dup.
+	 * For sysctl this should only happen for directory entries.
+	 */
+	for (head = sysctl_head_next(NULL); head; head = sysctl_head_next(head)) {
+		table = proc_sys_lookup_table(dentry, head->ctl_table);
+
+		if (!table)
+			continue;
+
+		for (; table->ctl_name || table->procname; table++, pos++) {
+			/* Can't do anything without a proc name */
+			if (!table->procname)
+				continue;
+
+			if (pos < filp->f_pos)
+				continue;
+
+			if (proc_sys_fill_cache(filp, dirent, filldir, table) < 0)
+				goto out;
+			filp->f_pos = pos + 1;
+		}
+	}
+	ret = 1;
+out:
+	sysctl_head_finish(head);
+	return ret;
+}
+
+static int proc_sys_permission(struct inode *inode, int mask, struct nameidata *nd)
+{
+	/*
+	 * sysctl entries that are not writeable,
+	 * are _NOT_ writeable, capabilities or not.
+	 */
+	struct ctl_table_header *head;
+	struct ctl_table *table;
+	struct dentry *dentry;
+	int mode;
+	int depth;
+	int error;
+
+	head = NULL;
+	depth = PROC_I(inode)->fd;
+
+	/* First check the cached permissions, in case we don't have
+	 * enough information to lookup the sysctl table entry.
+	 */
+	error = -EACCES;
+	mode = inode->i_mode;
+
+	if (current->euid == 0)
+		mode >>= 6;
+	else if (in_group_p(0))
+		mode >>= 3;
+
+	if ((mode & mask & (MAY_READ|MAY_WRITE|MAY_EXEC)) == mask)
+		error = 0;
+
+	/* If we can't get a sysctl table entry the permission
+	 * checks on the cached mode will have to be enough.
+	 */
+	if (!nd || !depth)
+		goto out;
+
+	dentry = nd->dentry;
+	table = do_proc_sys_lookup(dentry->d_parent, &dentry->d_name, &head);
+
+	/* If the entry does not exist deny permission */
+	error = -EACCES;
+	if (!table)
+		goto out;
+
+	/* Use the permissions on the sysctl table entry */
+	error = sysctl_perm(table, mask);
+out:
+	sysctl_head_finish(head);
+	return error;
+}
+
+static int proc_sys_setattr(struct dentry *dentry, struct iattr *attr)
+{
+	struct inode *inode = dentry->d_inode;
+	int error;
+
+	if (attr->ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID))
+		return -EPERM;
+
+	error = inode_change_ok(inode, attr);
+	if (!error) {
+		error = security_inode_setattr(dentry, attr);
+		if (!error)
+			error = inode_setattr(inode, attr);
+	}
+
+	return error;
+}
+
+/* I'm lazy and don't distinguish between files and directories,
+ * until access time.
+ */
+static const struct file_operations proc_sys_file_operations = {
+	.read		= proc_sys_read,
+	.write		= proc_sys_write,
+	.readdir	= proc_sys_readdir,
+};
+
+static struct inode_operations proc_sys_inode_operations = {
+	.lookup		= proc_sys_lookup,
+	.permission	= proc_sys_permission,
+	.setattr	= proc_sys_setattr,
+};
+
+static int proc_sys_revalidate(struct dentry *dentry, struct nameidata *nd)
+{
+	struct ctl_table_header *head;
+	struct ctl_table *table;
+	table = do_proc_sys_lookup(dentry->d_parent, &dentry->d_name, &head);
+	proc_sys_refresh_inode(dentry->d_inode, table);
+	sysctl_head_finish(head);
+	return !!table;
+}
+
+static struct dentry_operations proc_sys_dentry_operations = {
+	.d_revalidate	= proc_sys_revalidate,
+};
+
+static struct proc_dir_entry *proc_sys_root;
+
+int proc_sys_init(void)
+{
+	proc_sys_root = proc_mkdir("sys", NULL);
+	proc_sys_root->proc_iops = &proc_sys_inode_operations;
+	proc_sys_root->proc_fops = &proc_sys_file_operations;
+	proc_sys_root->nlink = 0;
+	return 0;
+}