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Subject[PATCH 2/4] tracing: Replace typecasted void pointer in set_ftrace_filter code
From: Steven Rostedt <srostedt@redhat.com>

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>
---
kernel/trace/ftrace.c | 67 +++++++++++++++++++++++++++++++++---------------
1 files changed, 46 insertions(+), 21 deletions(-)
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 585ea27..c8db0db 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;

--
1.7.1



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