tracing: Replace typecasted void pointer in set_ftrace_filter code

The set_ftrace_filter uses seq_file and reads from two lists. The
pointer returned by t_next() can either be of type struct dyn_ftrace
or struct ftrace_func_probe. If there is a bug (there was one)
the wrong pointer may be used and the reference can cause an oops.

This patch makes t_next() and friends only return the iterator structure
which now has a pointer of type struct dyn_ftrace and struct
ftrace_func_probe. The t_show() can now test if the pointer is NULL or
not and if the pointer exists, it is guaranteed to be of the correct type.

Now if there's a bug, only wrong data will be shown but not an oops.

Cc: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 46 insertions, 21 deletions

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 585ea27025b..c8db0dbb984 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1368,25 +1368,29 @@ enum {
 #define FTRACE_BUFF_MAX (KSYM_SYMBOL_LEN+4) /* room for wildcards */
 
 struct ftrace_iterator {
-        loff_t                  func_pos;
-        struct ftrace_page      *pg;
-        int                     hidx;
-        int                     idx;
-        unsigned                flags;
-        struct trace_parser     parser;
+        loff_t                          func_pos;
+        struct ftrace_page              *pg;
+        struct dyn_ftrace               *func;
+        struct ftrace_func_probe        *probe;
+        struct trace_parser             parser;
+        int                             hidx;
+        int                             idx;
+        unsigned                        flags;
 };
 
 static void *
-t_hash_next(struct seq_file *m, void *v, loff_t *pos)
+t_hash_next(struct seq_file *m, loff_t *pos)
 {
         struct ftrace_iterator *iter = m->private;
-        struct hlist_node *hnd = v;
+        struct hlist_node *hnd = NULL;
         struct hlist_head *hhd;
 
         WARN_ON(!(iter->flags & FTRACE_ITER_HASH));
 
         (*pos)++;
 
+        if (iter->probe)
+                hnd = &iter->probe->node;
  retry:
         if (iter->hidx >= FTRACE_FUNC_HASHSIZE)
                 return NULL;
@@ -1409,7 +1413,12 @@ t_hash_next(struct seq_file *m, void *v, loff_t *pos)
                 }
         }
 
-        return hnd;
+        if (WARN_ON_ONCE(!hnd))
+                return NULL;
+
+        iter->probe = hlist_entry(hnd, struct ftrace_func_probe, node);
+
+        return iter;
 }
 
 static void *t_hash_start(struct seq_file *m, loff_t *pos)
@@ -1428,19 +1437,24 @@ static void *t_hash_start(struct seq_file *m, loff_t *pos)
 
         iter->hidx = 0;
         for (l = 0; l <= (*pos - iter->func_pos); ) {
-                p = t_hash_next(m, p, &l);
+                p = t_hash_next(m, &l);
                 if (!p)
                         break;
         }
-        return p;
+        if (!p)
+                return NULL;
+
+        return iter;
 }
 
-static int t_hash_show(struct seq_file *m, void *v)
+static int
+t_hash_show(struct seq_file *m, struct ftrace_iterator *iter)
 {
         struct ftrace_func_probe *rec;
-        struct hlist_node *hnd = v;
 
-        rec = hlist_entry(hnd, struct ftrace_func_probe, node);
+        rec = iter->probe;
+        if (WARN_ON_ONCE(!rec))
+                return -EIO;
 
         if (rec->ops->print)
                 return rec->ops->print(m, rec->ip, rec->ops, rec->data);
@@ -1461,7 +1475,7 @@ t_next(struct seq_file *m, void *v, loff_t *pos)
         struct dyn_ftrace *rec = NULL;
 
         if (iter->flags & FTRACE_ITER_HASH)
-                return t_hash_next(m, v, pos);
+                return t_hash_next(m, pos);
 
         (*pos)++;
 
@@ -1495,7 +1509,12 @@ t_next(struct seq_file *m, void *v, loff_t *pos)
                 }
         }
 
-        return rec;
+        if (!rec)
+                return NULL;
+
+        iter->func = rec;
+
+        return iter;
 }
 
 static void *t_start(struct seq_file *m, loff_t *pos)
@@ -1530,10 +1549,14 @@ static void *t_start(struct seq_file *m, loff_t *pos)
                         break;
         }
 
-        if (!p && iter->flags & FTRACE_ITER_FILTER)
-                return t_hash_start(m, pos);
+        if (!p) {
+                if (iter->flags & FTRACE_ITER_FILTER)
+                        return t_hash_start(m, pos);
 
-        return p;
+                return NULL;
+        }
+
+        return iter;
 }
 
 static void t_stop(struct seq_file *m, void *p)
@@ -1544,16 +1567,18 @@ static void t_stop(struct seq_file *m, void *p)
 static int t_show(struct seq_file *m, void *v)
 {
         struct ftrace_iterator *iter = m->private;
-        struct dyn_ftrace *rec = v;
+        struct dyn_ftrace *rec;
 
         if (iter->flags & FTRACE_ITER_HASH)
-                return t_hash_show(m, v);
+                return t_hash_show(m, iter);
 
         if (iter->flags & FTRACE_ITER_PRINTALL) {
                 seq_printf(m, "#### all functions enabled ####\n");
                 return 0;
         }
 
+        rec = iter->func;
+
         if (!rec)
                 return 0;