[PATCH] sanitize proc_sysctl

* keep references to ctl_table_head and ctl_table in /proc/sys inodes
* grab the former during operations, use the latter for access to
  entry if that succeeds
* have ->d_compare() check if table should be seen for one who does lookup;
  that allows us to avoid flipping inodes - if we have the same name resolve
  to different things, we'll just keep several dentries and ->d_compare()
  will reject the wrong ones.
* have ->lookup() and ->readdir() scan the table of our inode first, then
  walk all ctl_table_header and scan ->attached_by for those that are
  attached to our directory.
* implement ->getattr().
* get rid of insane amounts of tree-walking
* get rid of the need to know dentry in ->permission() and of the contortions
  induced by that.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

2 files changed, 197 insertions, 235 deletions

diff --git a/fs/proc/inode.c b/fs/proc/inode.c
index b37f25dc45a5..8bb03f056c28 100644
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -17,6 +17,7 @@
 #include <linux/init.h>
 #include <linux/module.h>
 #include <linux/smp_lock.h>
+#include <linux/sysctl.h>
 
 #include <asm/system.h>
 #include <asm/uaccess.h>
@@ -65,6 +66,8 @@ static void proc_delete_inode(struct inode *inode)
                         module_put(de->owner);
                 de_put(de);
         }
+        if (PROC_I(inode)->sysctl)
+                sysctl_head_put(PROC_I(inode)->sysctl);
         clear_inode(inode);
 }
 
@@ -84,6 +87,8 @@ static struct inode *proc_alloc_inode(struct super_block *sb)
         ei->fd = 0;
         ei->op.proc_get_link = NULL;
         ei->pde = NULL;
+        ei->sysctl = NULL;
+        ei->sysctl_entry = NULL;
         inode = &ei->vfs_inode;
         inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
         return inode;
diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
index 5acc001d49f6..fa1ec2433e44 100644
--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -10,149 +10,110 @@
 static struct dentry_operations proc_sys_dentry_operations;
 static const struct file_operations proc_sys_file_operations;
 static const struct inode_operations proc_sys_inode_operations;
+static const struct file_operations proc_sys_dir_file_operations;
+static const struct inode_operations proc_sys_dir_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)
+static struct inode *proc_sys_make_inode(struct super_block *sb,
+                struct ctl_table_header *head, struct ctl_table *table)
 {
         struct inode *inode;
-        struct proc_inode *dir_ei, *ei;
-        int depth;
+        struct proc_inode *ei;
 
-        inode = new_inode(dir->i_sb);
+        inode = new_inode(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;
-
+        sysctl_head_get(head);
         ei = PROC_I(inode);
-        ei->fd = depth;
+        ei->sysctl = head;
+        ei->sysctl_entry = table;
+
         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;
         inode->i_flags |= S_PRIVATE; /* tell selinux to ignore this inode */
-        proc_sys_refresh_inode(inode, table);
+        inode->i_mode = table->mode;
+        if (!table->child) {
+                inode->i_mode |= S_IFREG;
+                inode->i_op = &proc_sys_inode_operations;
+                inode->i_fop = &proc_sys_file_operations;
+        } else {
+                inode->i_mode |= S_IFDIR;
+                inode->i_nlink = 0;
+                inode->i_op = &proc_sys_dir_operations;
+                inode->i_fop = &proc_sys_dir_file_operations;
+        }
 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)
+static struct ctl_table *find_in_table(struct ctl_table *p, struct qstr *name)
 {
         int len;
-        for ( ; table->ctl_name || table->procname; table++) {
+        for ( ; p->ctl_name || p->procname; p++) {
 
-                if (!table->procname)
+                if (!p->procname)
                         continue;
 
-                len = strlen(table->procname);
+                len = strlen(p->procname);
                 if (len != name->len)
                         continue;
 
-                if (memcmp(table->procname, name->name, len) != 0)
+                if (memcmp(p->procname, name->name, len) != 0)
                         continue;
 
                 /* I have a match */
-                return table;
+                return p;
         }
         return NULL;
 }
 
-static struct ctl_table *proc_sys_lookup_table(struct dentry *dentry,
-                                                struct ctl_table *table)
+struct ctl_table_header *grab_header(struct inode *inode)
 {
-        struct dentry *ancestor;
-        struct proc_inode *ei;
-        int depth, i;
+        if (PROC_I(inode)->sysctl)
+                return sysctl_head_grab(PROC_I(inode)->sysctl);
+        else
+                return sysctl_head_next(NULL);
+}
 
-        ei = PROC_I(dentry->d_inode);
-        depth = ei->fd;
+static struct dentry *proc_sys_lookup(struct inode *dir, struct dentry *dentry,
+                                        struct nameidata *nd)
+{
+        struct ctl_table_header *head = grab_header(dir);
+        struct ctl_table *table = PROC_I(dir)->sysctl_entry;
+        struct ctl_table_header *h = NULL;
+        struct qstr *name = &dentry->d_name;
+        struct ctl_table *p;
+        struct inode *inode;
+        struct dentry *err = ERR_PTR(-ENOENT);
 
-        if (depth == 0)
-                return table;
+        if (IS_ERR(head))
+                return ERR_CAST(head);
 
-        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;
+        if (table && !table->child) {
+                WARN_ON(1);
+                goto out;
         }
-        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;
+        table = table ? table->child : head->ctl_table;
 
-        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;
+        p = find_in_table(table, name);
+        if (!p) {
+                for (h = sysctl_head_next(NULL); h; h = sysctl_head_next(h)) {
+                        if (h->attached_to != table)
+                                continue;
+                        p = find_in_table(h->attached_by, name);
+                        if (p)
+                                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)
+        if (!p)
                 goto out;
 
         err = ERR_PTR(-ENOMEM);
-        inode = proc_sys_make_inode(dir, table);
+        inode = proc_sys_make_inode(dir->i_sb, h ? h : head, p);
+        if (h)
+                sysctl_head_finish(h);
+
         if (!inode)
                 goto out;
 
@@ -168,22 +129,14 @@ out:
 static ssize_t proc_sys_call_handler(struct file *filp, void __user *buf,
                 size_t count, loff_t *ppos, int write)
 {
-        struct dentry *dentry = filp->f_dentry;
-        struct ctl_table_header *head;
-        struct ctl_table *table;
+        struct inode *inode = filp->f_path.dentry->d_inode;
+        struct ctl_table_header *head = grab_header(inode);
+        struct ctl_table *table = PROC_I(inode)->sysctl_entry;
         ssize_t error;
         size_t 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;
+        if (IS_ERR(head))
+                return PTR_ERR(head);
 
         /*
          * At this point we know that the sysctl was not unregistered
@@ -193,6 +146,11 @@ static ssize_t proc_sys_call_handler(struct file *filp, void __user *buf,
         if (sysctl_perm(head->root, table, write ? MAY_WRITE : MAY_READ))
                 goto out;
 
+        /* if that can happen at all, it should be -EINVAL, not -EISDIR */
+        error = -EINVAL;
+        if (!table->proc_handler)
+                goto out;
+
         /* careful: calling conventions are nasty here */
         res = count;
         error = table->proc_handler(table, write, filp, buf, &res, ppos);
@@ -218,82 +176,86 @@ static ssize_t proc_sys_write(struct file *filp, const char __user *buf,
 
 
 static int proc_sys_fill_cache(struct file *filp, void *dirent,
-                                filldir_t filldir, struct ctl_table *table)
+                                filldir_t filldir,
+                                struct ctl_table_header *head,
+                                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);
+                child = d_alloc(dir, &qname);
+                if (child) {
+                        inode = proc_sys_make_inode(dir->d_sb, head, table);
+                        if (!inode) {
+                                dput(child);
+                                return -ENOMEM;
+                        } else {
+                                child->d_op = &proc_sys_dentry_operations;
+                                d_add(child, inode);
                         }
-                        if (child)
-                                dput(new);
-                        else
-                                child = new;
+                } else {
+                        return -ENOMEM;
                 }
         }
-        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;
-        }
+        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);
+        return !!filldir(dirent, qname.name, qname.len, filp->f_pos, ino, type);
+}
+
+static int scan(struct ctl_table_header *head, ctl_table *table,
+                unsigned long *pos, struct file *file,
+                void *dirent, filldir_t filldir)
+{
+
+        for (; table->ctl_name || table->procname; table++, (*pos)++) {
+                int res;
+
+                /* Can't do anything without a proc name */
+                if (!table->procname)
+                        continue;
+
+                if (*pos < file->f_pos)
+                        continue;
+
+                res = proc_sys_fill_cache(file, dirent, filldir, head, table);
+                if (res)
+                        return res;
+
+                file->f_pos = *pos + 1;
+        }
+        return 0;
 }
 
 static int proc_sys_readdir(struct file *filp, void *dirent, filldir_t filldir)
 {
-        struct dentry *dentry = filp->f_dentry;
+        struct dentry *dentry = filp->f_path.dentry;
         struct inode *inode = dentry->d_inode;
-        struct ctl_table_header *head = NULL;
-        struct ctl_table *table;
+        struct ctl_table_header *head = grab_header(inode);
+        struct ctl_table *table = PROC_I(inode)->sysctl_entry;
+        struct ctl_table_header *h = NULL;
         unsigned long pos;
-        int ret;
+        int ret = -EINVAL;
+
+        if (IS_ERR(head))
+                return PTR_ERR(head);
 
-        ret = -ENOTDIR;
-        if (!S_ISDIR(inode->i_mode))
+        if (table && !table->child) {
+                WARN_ON(1);
                 goto out;
+        }
+
+        table = table ? table->child : head->ctl_table;
 
         ret = 0;
         /* Avoid a switch here: arm builds fail with missing __cmpdi2 */
@@ -311,30 +273,17 @@ static int proc_sys_readdir(struct file *filp, void *dirent, filldir_t filldir)
         }
         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);
+        ret = scan(head, table, &pos, filp, dirent, filldir);
+        if (ret)
+                goto out;
 
-                if (!table)
+        for (h = sysctl_head_next(NULL); h; h = sysctl_head_next(h)) {
+                if (h->attached_to != 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 = scan(h, h->attached_by, &pos, filp, dirent, filldir);
+                if (ret) {
+                        sysctl_head_finish(h);
+                        break;
                 }
         }
         ret = 1;
@@ -349,47 +298,18 @@ static int proc_sys_permission(struct inode *inode, int mask, struct nameidata *
          * 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;
+        struct ctl_table_header *head = grab_header(inode);
+        struct ctl_table *table = PROC_I(inode)->sysctl_entry;
         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;
+        if (IS_ERR(head))
+                return PTR_ERR(head);
 
-        dentry = nd->path.dentry;
-        table = do_proc_sys_lookup(dentry->d_parent, &dentry->d_name, &head);
+        if (!table) /* global root - r-xr-xr-x */
+                error = mask & MAY_WRITE ? -EACCES : 0;
+        else /* Use the permissions on the sysctl table entry */
+                error = sysctl_perm(head->root, table, mask);
 
-        /* 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(head->root, table, mask);
-out:
         sysctl_head_finish(head);
         return error;
 }
@@ -409,33 +329,70 @@ static int proc_sys_setattr(struct dentry *dentry, struct iattr *attr)
         return error;
 }
 
-/* I'm lazy and don't distinguish between files and directories,
- * until access time.
- */
+static int proc_sys_getattr(struct vfsmount *mnt, struct dentry *dentry, struct kstat *stat)
+{
+        struct inode *inode = dentry->d_inode;
+        struct ctl_table_header *head = grab_header(inode);
+        struct ctl_table *table = PROC_I(inode)->sysctl_entry;
+
+        if (IS_ERR(head))
+                return PTR_ERR(head);
+
+        generic_fillattr(inode, stat);
+        if (table)
+                stat->mode = (stat->mode & S_IFMT) | table->mode;
+
+        sysctl_head_finish(head);
+        return 0;
+}
+
 static const struct file_operations proc_sys_file_operations = {
         .read           = proc_sys_read,
         .write          = proc_sys_write,
+};
+
+static const struct file_operations proc_sys_dir_file_operations = {
         .readdir        = proc_sys_readdir,
 };
 
 static const struct inode_operations proc_sys_inode_operations = {
+        .permission     = proc_sys_permission,
+        .setattr        = proc_sys_setattr,
+        .getattr        = proc_sys_getattr,
+};
+
+static const struct inode_operations proc_sys_dir_operations = {
         .lookup         = proc_sys_lookup,
         .permission     = proc_sys_permission,
         .setattr        = proc_sys_setattr,
+        .getattr        = proc_sys_getattr,
 };
 
 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;
+        return !PROC_I(dentry->d_inode)->sysctl->unregistering;
+}
+
+static int proc_sys_delete(struct dentry *dentry)
+{
+        return !!PROC_I(dentry->d_inode)->sysctl->unregistering;
+}
+
+static int proc_sys_compare(struct dentry *dir, struct qstr *qstr,
+                            struct qstr *name)
+{
+        struct dentry *dentry = container_of(qstr, struct dentry, d_name);
+        if (qstr->len != name->len)
+                return 1;
+        if (memcmp(qstr->name, name->name, name->len))
+                return 1;
+        return !sysctl_is_seen(PROC_I(dentry->d_inode)->sysctl);
 }
 
 static struct dentry_operations proc_sys_dentry_operations = {
         .d_revalidate   = proc_sys_revalidate,
+        .d_delete       = proc_sys_delete,
+        .d_compare      = proc_sys_compare,
 };
 
 static struct proc_dir_entry *proc_sys_root;
@@ -443,8 +400,8 @@ 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->proc_iops = &proc_sys_dir_operations;
+        proc_sys_root->proc_fops = &proc_sys_dir_file_operations;
         proc_sys_root->nlink = 0;
         return 0;
 }