On Thu, 2014-10-02 at 22:05 -0400, Richard Guy Briggs wrote:
> New tree rules copy the path twice and discard the intermediary copy.
>
> This saves one pointer at the expense of one path string copy.
>
> Signed-off-by: Richard Guy Briggs <r...@redhat.com>
> ---
> kernel/audit_tree.c | 9 +++++----
> kernel/auditfilter.c | 5 +++--
> 2 files changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/audit_tree.c b/kernel/audit_tree.c
> index bd418c4..ace72ed 100644
> --- a/kernel/audit_tree.c
> +++ b/kernel/audit_tree.c
> @@ -17,7 +17,7 @@ struct audit_tree {
> struct list_head list;
> struct list_head same_root;
> struct rcu_head head;
> - char pathname[];
> + char *pathname;
> };
>
> struct audit_chunk {
> @@ -70,11 +70,11 @@ static LIST_HEAD(prune_list);
>
> static struct fsnotify_group *audit_tree_group;
>
> -static struct audit_tree *alloc_tree(const char *s)
> +static struct audit_tree *alloc_tree(char *s)
> {
> struct audit_tree *tree;
>
> - tree = kmalloc(sizeof(struct audit_tree) + strlen(s) + 1, GFP_KERNEL);
> + tree = kmalloc(sizeof(struct audit_tree), GFP_KERNEL);
> if (tree) {
> atomic_set(&tree->count, 1);
> tree->goner = 0;
> @@ -83,7 +83,7 @@ static struct audit_tree *alloc_tree(const char *s)
> INIT_LIST_HEAD(&tree->list);
> INIT_LIST_HEAD(&tree->same_root);
> tree->root = NULL;
> - strcpy(tree->pathname, s);
> + tree->pathname = s;
> }
> return tree;
> }
> @@ -96,6 +96,7 @@ static inline void get_tree(struct audit_tree *tree)
> static inline void put_tree(struct audit_tree *tree)
> {
> if (atomic_dec_and_test(&tree->count))
> + kfree(tree->pathname);
> kfree_rcu(tree, head);
> }
Why does the tree need to be freed after an RCU grace period but the
pathname can be freed immediately? What's the locking/access that makes
this safe?
>
> diff --git a/kernel/auditfilter.c b/kernel/auditfilter.c
> index e3378a4..facd704 100644
> --- a/kernel/auditfilter.c
> +++ b/kernel/auditfilter.c
> @@ -534,9 +534,10 @@ static struct audit_entry *audit_data_to_entry(struct
> audit_rule_data *data,
> entry->rule.buflen += f->val;
>
> err = audit_make_tree(&entry->rule, str, f->op);
> - kfree(str);
> - if (err)
> + if (err) {
> + kfree(str);
> goto exit_free;
> + }
> break;
> case AUDIT_INODE:
> err = audit_to_inode(&entry->rule, f);
--
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