ftrace: Create ftrace_hash_empty() helper routine

There are two types of hashes in the ftrace_ops; one type
is the filter_hash and the other is the notrace_hash. Either
one may be null, meaning it has no elements. But when elements
are added, the hash is allocated.

Throughout the code, a check needs to be made to see if a hash
exists or the hash has elements, but the check if the hash exists
is usually missing causing the possible "NULL pointer dereference bug".

Add a helper routine called "ftrace_hash_empty()" that returns
true if the hash doesn't exist or its count is zero. As they mean
the same thing.

Last-bug-reported-by: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index a383d6c..e1ee07f 100644 (file)
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -999,6 +999,11 @@ static struct ftrace_page *ftrace_new_pgs;
 static struct ftrace_page      *ftrace_pages_start;
 static struct ftrace_page      *ftrace_pages;
 
+static bool ftrace_hash_empty(struct ftrace_hash *hash)
+{
+       return !hash || !hash->count;
+}
+
 static struct ftrace_func_entry *
 ftrace_lookup_ip(struct ftrace_hash *hash, unsigned long ip)
 {
@@ -1007,7 +1012,7 @@ ftrace_lookup_ip(struct ftrace_hash *hash, unsigned long ip)
        struct hlist_head *hhd;
        struct hlist_node *n;
 
-       if (!hash->count)
+       if (ftrace_hash_empty(hash))
                return NULL;
 
        if (hash->size_bits > 0)
@@ -1151,7 +1156,7 @@ alloc_and_copy_ftrace_hash(int size_bits, struct ftrace_hash *hash)
                return NULL;
 
        /* Empty hash? */
-       if (!hash || !hash->count)
+       if (ftrace_hash_empty(hash))
                return new_hash;
 
        size = 1 << hash->size_bits;
@@ -1276,9 +1281,9 @@ ftrace_ops_test(struct ftrace_ops *ops, unsigned long ip)
        filter_hash = rcu_dereference_raw(ops->filter_hash);
        notrace_hash = rcu_dereference_raw(ops->notrace_hash);
 
-       if ((!filter_hash || !filter_hash->count ||
+       if ((ftrace_hash_empty(filter_hash) ||
             ftrace_lookup_ip(filter_hash, ip)) &&
-           (!notrace_hash || !notrace_hash->count ||
+           (ftrace_hash_empty(notrace_hash) ||
             !ftrace_lookup_ip(notrace_hash, ip)))
                ret = 1;
        else
@@ -1371,7 +1376,7 @@ static void __ftrace_hash_rec_update(struct ftrace_ops *ops,
        if (filter_hash) {
                hash = ops->filter_hash;
                other_hash = ops->notrace_hash;
-               if (!hash || !hash->count)
+               if (ftrace_hash_empty(hash))
                        all = 1;
        } else {
                inc = !inc;
@@ -1381,7 +1386,7 @@ static void __ftrace_hash_rec_update(struct ftrace_ops *ops,
                 * If the notrace hash has no items,
                 * then there's nothing to do.
                 */
-               if (!hash || !hash->count)
+               if (ftrace_hash_empty(hash))
                        return;
        }
 
@@ -1398,8 +1403,8 @@ static void __ftrace_hash_rec_update(struct ftrace_ops *ops,
                        if (!other_hash || !ftrace_lookup_ip(other_hash, rec->ip))
                                match = 1;
                } else {
-                       in_hash = hash && !!ftrace_lookup_ip(hash, rec->ip);
-                       in_other_hash = other_hash && !!ftrace_lookup_ip(other_hash, rec->ip);
+                       in_hash = !!ftrace_lookup_ip(hash, rec->ip);
+                       in_other_hash = !!ftrace_lookup_ip(other_hash, rec->ip);
 
                        /*
                         *
@@ -1407,7 +1412,7 @@ static void __ftrace_hash_rec_update(struct ftrace_ops *ops,
                        if (filter_hash && in_hash && !in_other_hash)
                                match = 1;
                        else if (!filter_hash && in_hash &&
-                                (in_other_hash || !other_hash->count))
+                                (in_other_hash || ftrace_hash_empty(other_hash)))
                                match = 1;
                }
                if (!match)
@@ -1950,7 +1955,7 @@ static int ops_traces_mod(struct ftrace_ops *ops)
        struct ftrace_hash *hash;
 
        hash = ops->filter_hash;
-       return !!(!hash || !hash->count);
+       return ftrace_hash_empty(hash);
 }
 
 static int ftrace_update_code(struct module *mod)
@@ -2320,7 +2325,8 @@ static void *t_start(struct seq_file *m, loff_t *pos)
         * off, we can short cut and just print out that all
         * functions are enabled.
         */
-       if (iter->flags & FTRACE_ITER_FILTER && !ops->filter_hash->count) {
+       if (iter->flags & FTRACE_ITER_FILTER &&
+           ftrace_hash_empty(ops->filter_hash)) {
                if (*pos > 0)
                        return t_hash_start(m, pos);
                iter->flags |= FTRACE_ITER_PRINTALL;