[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 000000000000..bb16a1e78826
--- /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;
+}