sysctl: register only tables of sysctl files

Split the registration of a complex ctl_table array which may have
arbitrary numbers of directories (->child != NULL) and tables of files
into a series of simpler registrations that only register tables of files.

Graphically:

   register('dir', { + file-a
                     + file-b
                     + subdir1
                       + file-c
                     + subdir2
                       + file-d
                       + file-e })

is transformed into:
   wrapper->subheaders[0] = register('dir', {file1-a, file1-b})
   wrapper->subheaders[1] = register('dir/subdir1', {file-c})
   wrapper->subheaders[2] = register('dir/subdir2', {file-d, file-e})
   return wrapper

This guarantees that __register_sysctl_table will only see a simple
ctl_table array with all entries having (->child == NULL).

Care was taken to pass the original simple ctl_table arrays to
__register_sysctl_table whenever possible.

This change is derived from a similar patch written
by Lucrian Grijincu.

Inspired-by: Lucian Adrian Grijincu <lucian.grijincu@gmail.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

1 files changed, 147 insertions, 18 deletions

diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
index 9b91deeeb56c..6bab2ae9e395 100644
--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -882,7 +882,7 @@ static int sysctl_check_table(struct nsproxy *namespaces, struct ctl_table *tabl
 #endif /* CONFIG_SYSCTL_SYSCALL_CHECK */
 
 /**
- * __register_sysctl_table - register a sysctl table
+ * __register_sysctl_table - register a leaf sysctl table
  * @root: List of sysctl headers to register on
  * @namespaces: Data to compute which lists of sysctl entries are visible
  * @path: The path to the directory the sysctl table is in.
@@ -900,29 +900,19 @@ static int sysctl_check_table(struct nsproxy *namespaces, struct ctl_table *tabl
  *
  * maxlen - the maximum size in bytes of the data
  *
- * mode - the file permissions for the /proc/sys file, and for sysctl(2)
+ * mode - the file permissions for the /proc/sys file
  *
- * child - a pointer to the child sysctl table if this entry is a directory, or
- *         %NULL.
+ * child - must be %NULL.
  *
  * proc_handler - the text handler routine (described below)
  *
- * de - for internal use by the sysctl routines
- *
  * extra1, extra2 - extra pointers usable by the proc handler routines
  *
  * Leaf nodes in the sysctl tree will be represented by a single file
  * under /proc; non-leaf nodes will be represented by directories.
  *
- * sysctl(2) can automatically manage read and write requests through
- * the sysctl table.  The data and maxlen fields of the ctl_table
- * struct enable minimal validation of the values being written to be
- * performed, and the mode field allows minimal authentication.
- *
- * There must be a proc_handler routine for any terminal nodes
- * mirrored under /proc/sys (non-terminals are handled by a built-in
- * directory handler).  Several default handlers are available to
- * cover common cases -
+ * There must be a proc_handler routine for any terminal nodes.
+ * Several default handlers are available to cover common cases -
  *
  * proc_dostring(), proc_dointvec(), proc_dointvec_jiffies(),
  * proc_dointvec_userhz_jiffies(), proc_dointvec_minmax(),
@@ -1059,6 +1049,100 @@ static char *append_path(const char *path, char *pos, const char *name)
         return pos;
 }
 
+static int count_subheaders(struct ctl_table *table)
+{
+        int has_files = 0;
+        int nr_subheaders = 0;
+        struct ctl_table *entry;
+
+        /* special case: no directory and empty directory */
+        if (!table || !table->procname)
+                return 1;
+
+        for (entry = table; entry->procname; entry++) {
+                if (entry->child)
+                        nr_subheaders += count_subheaders(entry->child);
+                else
+                        has_files = 1;
+        }
+        return nr_subheaders + has_files;
+}
+
+static int register_leaf_sysctl_tables(const char *path, char *pos,
+        struct ctl_table_header ***subheader,
+        struct ctl_table_root *root, struct nsproxy *namespaces,
+        struct ctl_table *table)
+{
+        struct ctl_table *ctl_table_arg = NULL;
+        struct ctl_table *entry, *files;
+        int nr_files = 0;
+        int nr_dirs = 0;
+        int err = -ENOMEM;
+
+        for (entry = table; entry->procname; entry++) {
+                if (entry->child)
+                        nr_dirs++;
+                else
+                        nr_files++;
+        }
+
+        files = table;
+        /* If there are mixed files and directories we need a new table */
+        if (nr_dirs && nr_files) {
+                struct ctl_table *new;
+                files = kzalloc(sizeof(struct ctl_table) * (nr_files + 1),
+                                GFP_KERNEL);
+                if (!files)
+                        goto out;
+
+                ctl_table_arg = files;
+                for (new = files, entry = table; entry->procname; entry++) {
+                        if (entry->child)
+                                continue;
+                        *new = *entry;
+                        new++;
+                }
+        }
+
+        /* Register everything except a directory full of subdirectories */
+        if (nr_files || !nr_dirs) {
+                struct ctl_table_header *header;
+                header = __register_sysctl_table(root, namespaces, path, files);
+                if (!header) {
+                        kfree(ctl_table_arg);
+                        goto out;
+                }
+
+                /* Remember if we need to free the file table */
+                header->ctl_table_arg = ctl_table_arg;
+                **subheader = header;
+                (*subheader)++;
+        }
+
+        /* Recurse into the subdirectories. */
+        for (entry = table; entry->procname; entry++) {
+                char *child_pos;
+
+                if (!entry->child)
+                        continue;
+
+                err = -ENAMETOOLONG;
+                child_pos = append_path(path, pos, entry->procname);
+                if (!child_pos)
+                        goto out;
+
+                err = register_leaf_sysctl_tables(path, child_pos, subheader,
+                                                  root, namespaces, entry->child);
+                pos[0] = '\0';
+                if (err)
+                        goto out;
+        }
+        err = 0;
+out:
+        /* On failure our caller will unregister all registered subheaders */
+        return err;
+}
+
 /**
  * __register_sysctl_paths - register a sysctl table hierarchy
  * @root: List of sysctl headers to register on
@@ -1077,7 +1161,8 @@ struct ctl_table_header *__register_sysctl_paths(
         const struct ctl_path *path, struct ctl_table *table)
 {
         struct ctl_table *ctl_table_arg = table;
-        struct ctl_table_header *header = NULL;
+        int nr_subheaders = count_subheaders(table);
+        struct ctl_table_header *header = NULL, **subheaders, **subheader;
         const struct ctl_path *component;
         char *new_path, *pos;
 
@@ -1097,12 +1182,39 @@ struct ctl_table_header *__register_sysctl_paths(
                         goto out;
                 table = table->child;
         }
-        header = __register_sysctl_table(root, namespaces, new_path, table);
-        if (header)
+        if (nr_subheaders == 1) {
+                header = __register_sysctl_table(root, namespaces, new_path, table);
+                if (header)
+                        header->ctl_table_arg = ctl_table_arg;
+        } else {
+                header = kzalloc(sizeof(*header) +
+                                 sizeof(*subheaders)*nr_subheaders, GFP_KERNEL);
+                if (!header)
+                        goto out;
+
+                subheaders = (struct ctl_table_header **) (header + 1);
+                subheader = subheaders;
                 header->ctl_table_arg = ctl_table_arg;
+
+                if (register_leaf_sysctl_tables(new_path, pos, &subheader,
+                                                root, namespaces, table))
+                        goto err_register_leaves;
+        }
+
 out:
         kfree(new_path);
         return header;
+
+err_register_leaves:
+        while (subheader > subheaders) {
+                struct ctl_table_header *subh = *(--subheader);
+                struct ctl_table *table = subh->ctl_table_arg;
+                unregister_sysctl_table(subh);
+                kfree(table);
+        }
+        kfree(header);
+        header = NULL;
+        goto out;
 }
 
 /**
@@ -1149,11 +1261,28 @@ EXPORT_SYMBOL(register_sysctl_table);
  */
 void unregister_sysctl_table(struct ctl_table_header * header)
 {
+        int nr_subheaders;
         might_sleep();
 
         if (header == NULL)
                 return;
 
+        nr_subheaders = count_subheaders(header->ctl_table_arg);
+        if (unlikely(nr_subheaders > 1)) {
+                struct ctl_table_header **subheaders;
+                int i;
+
+                subheaders = (struct ctl_table_header **)(header + 1);
+                for (i = nr_subheaders -1; i >= 0; i--) {
+                        struct ctl_table_header *subh = subheaders[i];
+                        struct ctl_table *table = subh->ctl_table_arg;
+                        unregister_sysctl_table(subh);
+                        kfree(table);
+                }
+                kfree(header);
+                return;
+        }
+
         spin_lock(&sysctl_lock);
         start_unregistering(header);
         if (!--header->parent->count) {