audit: allow audit code to satisfy getname requests from its names_list

Currently, if we call getname() on a userland string more than once,
we'll get multiple copies of the string and multiple audit_names
records.

Add a function that will allow the audit_names code to satisfy getname
requests using info from the audit_names list, avoiding a new allocation
and audit_names records.
Signed-off-by: NJeff Layton <jlayton@redhat.com>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

fs/namei.c

@@ -130,6 +130,10 @@ getname_flags(const char __user *filename, int flags, int *empty)
 	char *kname;
 	int len;
 
+	result = audit_reusename(filename);
+	if (result)
+		return result;
+
 	/* FIXME: create dedicated slabcache? */
 	result = kzalloc(sizeof(*result), GFP_KERNEL);
 	if (unlikely(!result))

include/linux/audit.h

@@ -471,6 +471,7 @@ extern void __audit_syscall_entry(int arch,
 				  int major, unsigned long a0, unsigned long a1,
 				  unsigned long a2, unsigned long a3);
 extern void __audit_syscall_exit(int ret_success, long ret_value);
+extern struct filename *__audit_reusename(const __user char *uptr);
 extern void __audit_getname(struct filename *name);
 extern void audit_putname(struct filename *name);
 extern void __audit_inode(const char *name, const struct dentry *dentry,
@@ -507,6 +508,12 @@ static inline void audit_syscall_exit(void *pt_regs)
 		__audit_syscall_exit(success, return_code);
 	}
 }
+static inline struct filename *audit_reusename(const __user char *name)
+{
+	if (unlikely(!audit_dummy_context()))
+		return __audit_reusename(name);
+	return NULL;
+}
 static inline void audit_getname(struct filename *name)
 {
 	if (unlikely(!audit_dummy_context()))
@@ -665,6 +672,10 @@ static inline int audit_dummy_context(void)
 {
 	return 1;
 }
+static inline struct filename *audit_reusename(const __user char *name)
+{
+	return NULL;
+}
 static inline void audit_getname(struct filename *name)
 { }
 static inline void audit_putname(struct filename *name)

kernel/auditsc.c

@@ -2020,6 +2020,29 @@ static struct audit_names *audit_alloc_name(struct audit_context *context,
 	return aname;
 }
 
+/**
+ * audit_reusename - fill out filename with info from existing entry
+ * @uptr: userland ptr to pathname
+ *
+ * Search the audit_names list for the current audit context. If there is an
+ * existing entry with a matching "uptr" then return the filename
+ * associated with that audit_name. If not, return NULL.
+ */
+struct filename *
+__audit_reusename(const __user char *uptr)
+{
+	struct audit_context *context = current->audit_context;
+	struct audit_names *n;
+
+	list_for_each_entry(n, &context->names_list, list) {
+		if (!n->name)
+			continue;
+		if (n->name->uptr == uptr)
+			return n->name;
+	}
+	return NULL;
+}
+
 /**
  * audit_getname - add a name to the list
  * @name: name to add