audit: replace getname()/putname() hacks with reference counters

In order to ensure that filenames are not released before the audit
subsystem is done with the strings there are a number of hacks built
into the fs and audit subsystems around getname() and putname().  To
say these hacks are "ugly" would be kind.

This patch removes the filename hackery in favor of a more
conventional reference count based approach.  The diffstat below tells
most of the story; lots of audit/fs specific code is replaced with a
traditional reference count based approach that is easily understood,
even by those not familiar with the audit and/or fs subsystems.

CC: viro@zeniv.linux.org.uk
CC: linux-fsdevel@vger.kernel.org
Signed-off-by: Paul Moore <pmoore@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

2 files changed, 13 insertions, 109 deletions

diff --git a/kernel/audit.h b/kernel/audit.h
index 3cdffad..1caa0d3 100644
--- a/kernel/audit.h
+++ b/kernel/audit.h
@@ -24,12 +24,6 @@
 #include <linux/skbuff.h>
 #include <uapi/linux/mqueue.h>
 
-/* 0 = no checking
-   1 = put_count checking
-   2 = verbose put_count checking
-*/
-#define AUDIT_DEBUG 0
-
 /* AUDIT_NAMES is the number of slots we reserve in the audit_context
  * for saving names from getname().  If we get more names we will allocate
  * a name dynamically and also add those to the list anchored by names_list. */
@@ -74,9 +68,8 @@ struct audit_cap_data {
 	};
 };
 
-/* When fs/namei.c:getname() is called, we store the pointer in name and
- * we don't let putname() free it (instead we free all of the saved
- * pointers at syscall exit time).
+/* When fs/namei.c:getname() is called, we store the pointer in name and bump
+ * the refcnt in the associated filename struct.
  *
  * Further, in fs/namei.c:path_lookup() we store the inode and device.
  */
@@ -86,7 +79,6 @@ struct audit_names {
 	struct filename		*name;
 	int			name_len;	/* number of chars to log */
 	bool			hidden;		/* don't log this record */
-	bool			name_put;	/* call __putname()? */
 
 	unsigned long		ino;
 	dev_t			dev;
@@ -208,11 +200,6 @@ struct audit_context {
 	};
 	int fds[2];
 	struct audit_proctitle proctitle;
-
-#if AUDIT_DEBUG
-	int		    put_count;
-	int		    ino_count;
-#endif
 };
 
 extern u32 audit_ever_enabled;
diff --git a/kernel/auditsc.c b/kernel/auditsc.c
index 4f52196..0c38604 100644
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c
@@ -866,33 +866,10 @@ static inline void audit_free_names(struct audit_context *context)
 {
 	struct audit_names *n, *next;
 
-#if AUDIT_DEBUG == 2
-	if (context->put_count + context->ino_count != context->name_count) {
-		int i = 0;
-
-		pr_err("%s:%d(:%d): major=%d in_syscall=%d"
-		       " name_count=%d put_count=%d ino_count=%d"
-		       " [NOT freeing]\n", __FILE__, __LINE__,
-		       context->serial, context->major, context->in_syscall,
-		       context->name_count, context->put_count,
-		       context->ino_count);
-		list_for_each_entry(n, &context->names_list, list) {
-			pr_err("names[%d] = %p = %s\n", i++, n->name,
-			       n->name->name ?: "(null)");
-		}
-		dump_stack();
-		return;
-	}
-#endif
-#if AUDIT_DEBUG
-	context->put_count  = 0;
-	context->ino_count  = 0;
-#endif
-
 	list_for_each_entry_safe(n, next, &context->names_list, list) {
 		list_del(&n->list);
-		if (n->name && n->name_put)
-			final_putname(n->name);
+		if (n->name)
+			putname(n->name);
 		if (n->should_free)
 			kfree(n);
 	}
@@ -1711,9 +1688,6 @@ static struct audit_names *audit_alloc_name(struct audit_context *context,
 	list_add_tail(&aname->list, &context->names_list);
 
 	context->name_count++;
-#if AUDIT_DEBUG
-	context->ino_count++;
-#endif
 	return aname;
 }
 
@@ -1734,8 +1708,10 @@ __audit_reusename(const __user char *uptr)
 	list_for_each_entry(n, &context->names_list, list) {
 		if (!n->name)
 			continue;
-		if (n->name->uptr == uptr)
+		if (n->name->uptr == uptr) {
+			n->name->refcnt++;
 			return n->name;
+		}
 	}
 	return NULL;
 }
@@ -1752,19 +1728,8 @@ void __audit_getname(struct filename *name)
 	struct audit_context *context = current->audit_context;
 	struct audit_names *n;
 
-	if (!context->in_syscall) {
-#if AUDIT_DEBUG == 2
-		pr_err("%s:%d(:%d): ignoring getname(%p)\n",
-		       __FILE__, __LINE__, context->serial, name);
-		dump_stack();
-#endif
+	if (!context->in_syscall)
 		return;
-	}
-
-#if AUDIT_DEBUG
-	/* The filename _must_ have a populated ->name */
-	BUG_ON(!name->name);
-#endif
 
 	n = audit_alloc_name(context, AUDIT_TYPE_UNKNOWN);
 	if (!n)
@@ -1772,56 +1737,13 @@ void __audit_getname(struct filename *name)
 
 	n->name = name;
 	n->name_len = AUDIT_NAME_FULL;
-	n->name_put = true;
 	name->aname = n;
+	name->refcnt++;
 
 	if (!context->pwd.dentry)
 		get_fs_pwd(current->fs, &context->pwd);
 }
 
-/* audit_putname - intercept a putname request
- * @name: name to intercept and delay for putname
- *
- * If we have stored the name from getname in the audit context,
- * then we delay the putname until syscall exit.
- * Called from include/linux/fs.h:putname().
- */
-void audit_putname(struct filename *name)
-{
-	struct audit_context *context = current->audit_context;
-
-	BUG_ON(!context);
-	if (!name->aname || !context->in_syscall) {
-#if AUDIT_DEBUG == 2
-		pr_err("%s:%d(:%d): final_putname(%p)\n",
-		       __FILE__, __LINE__, context->serial, name);
-		if (context->name_count) {
-			struct audit_names *n;
-			int i = 0;
-
-			list_for_each_entry(n, &context->names_list, list)
-				pr_err("name[%d] = %p = %s\n", i++, n->name,
-				       n->name->name ?: "(null)");
-			}
-#endif
-		final_putname(name);
-	}
-#if AUDIT_DEBUG
-	else {
-		++context->put_count;
-		if (context->put_count > context->name_count) {
-			pr_err("%s:%d(:%d): major=%d in_syscall=%d putname(%p)"
-			       " name_count=%d put_count=%d\n",
-			       __FILE__, __LINE__,
-			       context->serial, context->major,
-			       context->in_syscall, name->name,
-			       context->name_count, context->put_count);
-			dump_stack();
-		}
-	}
-#endif
-}
-
 /**
  * __audit_inode - store the inode and device from a lookup
  * @name: name being audited
@@ -1842,11 +1764,6 @@ void __audit_inode(struct filename *name, const struct dentry *dentry,
 	if (!name)
 		goto out_alloc;
 
-#if AUDIT_DEBUG
-	/* The struct filename _must_ have a populated ->name */
-	BUG_ON(!name->name);
-#endif
-
 	/*
 	 * If we have a pointer to an audit_names entry already, then we can
 	 * just use it directly if the type is correct.
@@ -1893,9 +1810,10 @@ out_alloc:
 	n = audit_alloc_name(context, AUDIT_TYPE_UNKNOWN);
 	if (!n)
 		return;
-	if (name)
-		/* no need to set ->name_put as the original will cleanup */
+	if (name) {
 		n->name = name;
+		name->refcnt++;
+	}
 
 out:
 	if (parent) {
@@ -2000,8 +1918,7 @@ void __audit_inode_child(const struct inode *parent,
 		if (found_parent) {
 			found_child->name = found_parent->name;
 			found_child->name_len = AUDIT_NAME_FULL;
-			/* don't call __putname() */
-			found_child->name_put = false;
+			found_child->name->refcnt++;
 		}
 	}