[v2 077/115] sysctl: add duplicate entry and sanity ctl_table checks

[Lucian Adrian Grijincu <lucian.grijincu@gmail.com>]

Signed-off-by: Lucian Adrian Grijincu <lucian.grijincu@gmail.com>
---
 include/linux/sysctl.h |    7 ++
 kernel/sysctl.c        |   19 ++++++-
 kernel/sysctl_check.c  |  153 +++++++++++++++++++++++++++++++++++++++++++++++-
 3 files changed, 177 insertions(+), 2 deletions(-)

diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index b626271..22b6eb8 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -1092,6 +1092,13 @@ extern struct ctl_table_header *register_sysctl_paths(const struct ctl_path *pat
 						      struct ctl_table *table);
 extern void unregister_sysctl_table(struct ctl_table_header *table);
 
+#ifdef CONFIG_SYSCTL_SYSCALL_CHECK
+extern int sysctl_check_table(const struct ctl_path *path,
+			      int nr_dirs,
+			      struct ctl_table *table);
+extern int sysctl_check_duplicates(struct ctl_table_header *header);
+#endif /* CONFIG_SYSCTL_SYSCALL_CHECK */
+
 #endif /* __KERNEL__ */
 
 #endif /* _LINUX_SYSCTL_H */
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index cbf33b1..d777e89 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1977,8 +1977,14 @@ struct ctl_table_header *__register_sysctl_paths(struct ctl_table_group *group,
 	const struct ctl_path *path, struct ctl_table *table)
 {
 	struct ctl_table_header *header;
+	int failed_duplicate_check = 0;
 	int nr_dirs = ctl_path_items(path);
 
+#ifdef CONFIG_SYSCTL_SYSCALL_CHECK
+	if (sysctl_check_table(path, nr_dirs, table))
+		return NULL;
+#endif
+
 	header = alloc_sysctl_header(group);
 	if (!header)
 		return NULL;
@@ -1993,9 +1999,20 @@ struct ctl_table_header *__register_sysctl_paths(struct ctl_table_group *group,
 	header->ctl_header_refs = 1;
 
 	sysctl_write_lock_head(header->parent);
-	list_add_tail(&header->ctl_entry, &header->parent->ctl_tables);
+
+#ifdef CONFIG_SYSCTL_SYSCALL_CHECK
+	failed_duplicate_check = sysctl_check_duplicates(header);
+#endif
+	if (!failed_duplicate_check)
+		list_add_tail(&header->ctl_entry, &header->parent->ctl_tables);
+
 	sysctl_write_unlock_head(header->parent);
 
+	if (failed_duplicate_check) {
+		unregister_sysctl_table(header);
+		return NULL;
+	}
+
 	return header;
 }
 
diff --git a/kernel/sysctl_check.c b/kernel/sysctl_check.c
index e9a7a58..4e0bce5 100644
--- a/kernel/sysctl_check.c
+++ b/kernel/sysctl_check.c
@@ -1 +1,152 @@
-/* will be rewritten */
+#include <linux/sysctl.h>
+#include <linux/string.h>
+
+/*
+ * @path: the path to the offender
+ * @offender is the name of a file or directory that violated some sysctl rules.
+ * @str: a message accompanying the error
+ */
+static void fail(const struct ctl_path *path,
+		 const char *offender,
+		 const char *str)
+{
+	printk(KERN_ERR "sysctl sanity check failed: ");
+
+	for (; path->procname; path++)
+		printk("/%s", path->procname);
+
+	if (offender)
+		printk("/%s", offender);
+
+	printk(": %s\n", str);
+}
+
+#define FAIL(str) do { fail(path, t->procname, str); error = -EINVAL;} while (0)
+
+int sysctl_check_table(const struct ctl_path *path,
+		       int nr_dirs,
+		       struct ctl_table *table)
+{
+	struct ctl_table *t;
+	int error = 0;
+
+	if (nr_dirs > CTL_MAXNAME - 1) {
+		fail(path, NULL, "tree too deep");
+		error = -EINVAL;
+	}
+
+	for(t = table; t->procname; t++) {
+		if ((t->proc_handler == proc_dostring) ||
+		    (t->proc_handler == proc_dointvec) ||
+		    (t->proc_handler == proc_dointvec_minmax) ||
+		    (t->proc_handler == proc_dointvec_jiffies) ||
+		    (t->proc_handler == proc_dointvec_userhz_jiffies) ||
+		    (t->proc_handler == proc_dointvec_ms_jiffies) ||
+		    (t->proc_handler == proc_doulongvec_minmax) ||
+		    (t->proc_handler == proc_doulongvec_ms_jiffies_minmax)) {
+			if (!t->data)
+				FAIL("No data");
+			if (!t->maxlen)
+				FAIL("No maxlen");
+		}
+#ifdef CONFIG_PROC_SYSCTL
+		if (!t->proc_handler)
+			FAIL("No proc_handler");
+#endif
+		if (t->mode > 0777)
+			FAIL("bogus .mode");
+	}
+
+	if (error)
+		dump_stack();
+
+	return error;
+}
+
+
+/*
+ * @dir: the directory imediately above the offender
+ * @offender is the name of a file or directory that violated some sysctl rules.
+ */
+static void duplicate_error(struct ctl_table_header *dir,
+			    const char *offender)
+{
+	const char *names[CTL_MAXNAME];
+	int i = 0;
+
+	printk(KERN_ERR "sysctl duplicate check failed: ");
+
+	for (; dir->parent; dir = dir->parent)
+		/* ctl_dirname can be NULL: netns-correspondent
+		 * directories do not have a ctl_dirname. Their only
+		 * pourpose is to hold the list of
+		 * subdirs/subtables. They hold netns-specific
+		 * information for the parent directory. */
+		if (dir->ctl_dirname) {
+			names[i] = dir->ctl_dirname;
+			i++;
+		}
+
+	/* Print the names in the normal path order, not reversed */
+	for(i--; i >= 0; i--)
+		printk("/%s", names[i]);
+
+	printk("/%s \n", offender);
+}
+
+/* is there an entry in the table with the same procname? */
+static int match(struct ctl_table *table, const char *name)
+{
+	for ( ; table->procname; table++) {
+
+		if (strcmp(table->procname, name) == 0)
+			return 1;
+	}
+	return 0;
+}
+
+
+/* Called under header->parent write lock.
+ *
+ * checks whether this header's table introduces items that have the
+ * same names as other items at the same level (other files or
+ * subdirectories of the current dir). */
+int sysctl_check_duplicates(struct ctl_table_header *header)
+{
+	int has_duplicates = 0;
+	struct ctl_table *table = header->ctl_table_arg;
+	struct ctl_table_header *dir = header->parent;
+	struct ctl_table_header *h;
+
+	list_for_each_entry(h, &dir->ctl_subdirs, ctl_entry) {
+		if (IS_ERR(sysctl_use_header(h)))
+			continue;
+
+		if (match(table, h->ctl_dirname)) {
+			has_duplicates = 1;
+			duplicate_error(dir, h->ctl_dirname);
+		}
+
+		sysctl_unuse_header(h);
+	}
+
+	list_for_each_entry(h, &dir->ctl_tables, ctl_entry) {
+		ctl_table *t;
+
+		if (IS_ERR(sysctl_use_header(h)))
+			continue;
+
+		for (t = h->ctl_table_arg; t->procname; t++) {
+			if (match(table, t->procname)) {
+				has_duplicates = 1;
+				duplicate_error(dir, t->procname);
+			}
+		}
+		sysctl_unuse_header(h);
+	}
+
+	if (has_duplicates)
+		dump_stack();
+
+	return has_duplicates;
+}
-- 
1.7.5.134.g1c08b