sysctl: Rewrite proc_sys_readdir in terms of first_entry and next_entry

Replace sysctl_head_next with first_entry and next_entry.  These new
iterators operate at the level of sysctl table entries and filter
out any sysctl tables that should not be shown.

Utilizing two specialized functions instead of a single function removes
conditionals for handling awkward special cases that only come up
at the beginning of iteration, making the iterators easier to read
and understand.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

1 files changed, 62 insertions, 36 deletions

diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
index 3b63f298ce28..d9c3ae6afe4c 100644
--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -243,31 +243,25 @@ static struct ctl_table *lookup_entry(struct ctl_table_header **phead,
         return entry;
 }
 
-static struct ctl_table_header *__sysctl_head_next(struct nsproxy *namespaces,
-                                                struct ctl_table_header *prev)
+static struct ctl_table_header *next_usable_entry(struct ctl_table *dir,
+        struct ctl_table_root *root, struct list_head *tmp)
 {
-        struct ctl_table_root *root;
+        struct nsproxy *namespaces = current->nsproxy;
         struct list_head *header_list;
         struct ctl_table_header *head;
-        struct list_head *tmp;
 
-        spin_lock(&sysctl_lock);
-        if (prev) {
-                head = prev;
-                tmp = &prev->ctl_entry;
-                unuse_table(prev);
-                goto next;
-        }
-        tmp = &root_table_header.ctl_entry;
+        goto next;
         for (;;) {
                 head = list_entry(tmp, struct ctl_table_header, ctl_entry);
+                root = head->root;
 
-                if (!use_table(head))
+                if (head->attached_to != dir ||
+                    !head->attached_by->procname ||
+                    !use_table(head))
                         goto next;
-                spin_unlock(&sysctl_lock);
+
                 return head;
         next:
-                root = head->root;
                 tmp = tmp->next;
                 header_list = lookup_header_list(root, namespaces);
                 if (tmp != header_list)
@@ -283,13 +277,53 @@ static struct ctl_table_header *__sysctl_head_next(struct nsproxy *namespaces,
                 tmp = header_list->next;
         }
 out:
-        spin_unlock(&sysctl_lock);
         return NULL;
 }
 
-static struct ctl_table_header *sysctl_head_next(struct ctl_table_header *prev)
+static void first_entry(
+        struct ctl_table_header *dir_head, struct ctl_table *dir,
+        struct ctl_table_header **phead, struct ctl_table **pentry)
 {
-        return __sysctl_head_next(current->nsproxy, prev);
+        struct ctl_table_header *head = dir_head;
+        struct ctl_table *entry = dir;
+
+        spin_lock(&sysctl_lock);
+        if (entry->procname) {
+                use_table(head);
+        } else {
+                head = next_usable_entry(dir, &sysctl_table_root,
+                                         &sysctl_table_root.default_set.list);
+                if (head)
+                        entry = head->attached_by;
+        }
+        spin_unlock(&sysctl_lock);
+        *phead = head;
+        *pentry = entry;
+}
+
+static void next_entry(struct ctl_table *dir,
+        struct ctl_table_header **phead, struct ctl_table **pentry)
+{
+        struct ctl_table_header *head = *phead;
+        struct ctl_table *entry = *pentry;
+
+        entry++;
+        if (!entry->procname) {
+                struct ctl_table_root *root = head->root;
+                struct list_head *tmp = &head->ctl_entry;
+                if (head->attached_to != dir) {
+                        root = &sysctl_table_root;
+                        tmp = &sysctl_table_root.default_set.list;
+                }
+                spin_lock(&sysctl_lock);
+                unuse_table(head);
+                head = next_usable_entry(dir, root, tmp);
+                spin_unlock(&sysctl_lock);
+                if (head)
+                        entry = head->attached_by;
+        }
+        *phead = head;
+        *pentry = entry;
 }
 
 void register_sysctl_root(struct ctl_table_root *root)
@@ -533,20 +567,17 @@ static int scan(struct ctl_table_header *head, ctl_table *table,
                 unsigned long *pos, struct file *file,
                 void *dirent, filldir_t filldir)
 {
+        int res;
 
-        for (; table->procname; table++, (*pos)++) {
-                int res;
+        if ((*pos)++ < file->f_pos)
+                return 0;
 
-                if (*pos < file->f_pos)
-                        continue;
+        res = proc_sys_fill_cache(file, dirent, filldir, head, table);
 
-                res = proc_sys_fill_cache(file, dirent, filldir, head, table);
-                if (res)
-                        return res;
+        if (res == 0)
+                file->f_pos = *pos;
 
-                file->f_pos = *pos + 1;
-        }
-        return 0;
+        return res;
 }
 
 static int proc_sys_readdir(struct file *filp, void *dirent, filldir_t filldir)
@@ -556,6 +587,7 @@ static int proc_sys_readdir(struct file *filp, void *dirent, filldir_t filldir)
         struct ctl_table_header *head = grab_header(inode);
         struct ctl_table *table = PROC_I(inode)->sysctl_entry;
         struct ctl_table_header *h = NULL;
+        struct ctl_table *entry;
         unsigned long pos;
         int ret = -EINVAL;
 
@@ -585,14 +617,8 @@ static int proc_sys_readdir(struct file *filp, void *dirent, filldir_t filldir)
         }
         pos = 2;
 
-        ret = scan(head, table, &pos, filp, dirent, filldir);
-        if (ret)
-                goto out;
-
-        for (h = sysctl_head_next(NULL); h; h = sysctl_head_next(h)) {
-                if (h->attached_to != table)
-                        continue;
-                ret = scan(h, h->attached_by, &pos, filp, dirent, filldir);
+        for (first_entry(head, table, &h, &entry); h; next_entry(table, &h, &entry)) {
+                ret = scan(h, entry, &pos, filp, dirent, filldir);
                 if (ret) {
                         sysctl_head_finish(h);
                         break;