[PATCH 2/4] ftrace: Protect direct_functions in update_ftrace_direct_del

[Leon Hwang]

Fix accessing the __rcu pointer direct_functions with RCU protection.

Cc: sta...@vger.kernel.org
Fixes: 8d2c1233f371 ("ftrace: Add update_ftrace_direct_del function")
Signed-off-by: Leon Hwang <leon.hw...@linux.dev>
---
 kernel/trace/ftrace.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index c5d1d0d42ccc..9ea39110927f 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -6512,6 +6512,7 @@ int update_ftrace_direct_del(struct ftrace_ops *ops, 
struct ftrace_hash *hash)
        struct ftrace_hash *new_direct_functions;
        struct ftrace_hash *new_filter_hash = NULL;
        struct ftrace_hash *old_filter_hash;
+       struct ftrace_hash *direct_hash;
        struct ftrace_func_entry *entry;
        struct ftrace_func_entry *del;
        unsigned long size;
@@ -6523,11 +6524,13 @@ int update_ftrace_direct_del(struct ftrace_ops *ops, 
struct ftrace_hash *hash)
                return -EINVAL;
        if (!(ops->flags & FTRACE_OPS_FL_ENABLED))
                return -EINVAL;
-       if (direct_functions == EMPTY_HASH)
-               return -EINVAL;
 
        mutex_lock(&direct_mutex);
 
+       direct_hash = rcu_dereference_protected(direct_functions, 
lockdep_is_held(&direct_mutex));
+       if (direct_hash == EMPTY_HASH)
+               goto out_unlock;
+
        old_filter_hash = ops->func_hash ? ops->func_hash->filter_hash : NULL;
 
        if (!hash_count(old_filter_hash))
@@ -6537,7 +6540,7 @@ int update_ftrace_direct_del(struct ftrace_ops *ops, 
struct ftrace_hash *hash)
        size = 1 << hash->size_bits;
        for (int i = 0; i < size; i++) {
                hlist_for_each_entry(entry, &hash->buckets[i], hlist) {
-                       del = __ftrace_lookup_ip(direct_functions, entry->ip);
+                       del = __ftrace_lookup_ip(direct_hash, entry->ip);
                        if (!del || del->direct != entry->direct)
                                goto out_unlock;
                }
@@ -6548,7 +6551,7 @@ int update_ftrace_direct_del(struct ftrace_ops *ops, 
struct ftrace_hash *hash)
        if (!new_filter_hash)
                goto out_unlock;
 
-       new_direct_functions = hash_sub(direct_functions, hash);
+       new_direct_functions = hash_sub(direct_hash, hash);
        if (!new_direct_functions)
                goto out_unlock;
 
@@ -6575,7 +6578,7 @@ int update_ftrace_direct_del(struct ftrace_ops *ops, 
struct ftrace_hash *hash)
                /* free the new_direct_functions */
                old_direct_functions = new_direct_functions;
        } else {
-               old_direct_functions = direct_functions;
+               old_direct_functions = direct_hash;
                rcu_assign_pointer(direct_functions, new_direct_functions);
        }
 
-- 
2.55.0