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>

1 files changed, 14 insertions, 15 deletions

diff --git a/fs/namei.c b/fs/namei.c
index a3fde77..96ca11d 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -118,15 +118,6 @@
  * POSIX.1 2.4: an empty pathname is invalid (ENOENT).
  * PATH_MAX includes the nul terminator --RR.
  */
-void final_putname(struct filename *name)
-{
-	if (name->separate) {
-		__putname(name->name);
-		kfree(name);
-	} else {
-		__putname(name);
-	}
-}
 
 #define EMBEDDED_NAME_MAX	(PATH_MAX - sizeof(struct filename))
 
@@ -145,6 +136,7 @@ getname_flags(const char __user *filename, int flags, int *empty)
 	result = __getname();
 	if (unlikely(!result))
 		return ERR_PTR(-ENOMEM);
+	result->refcnt = 1;
 
 	/*
 	 * First, try to embed the struct filename inside the names_cache
@@ -179,6 +171,7 @@ recopy:
 		}
 		result->name = kname;
 		result->separate = true;
+		result->refcnt = 1;
 		max = PATH_MAX;
 		goto recopy;
 	}
@@ -202,7 +195,7 @@ recopy:
 	return result;
 
 error:
-	final_putname(result);
+	putname(result);
 	return err;
 }
 
@@ -243,19 +236,25 @@ getname_kernel(const char * filename)
 	memcpy((char *)result->name, filename, len);
 	result->uptr = NULL;
 	result->aname = NULL;
+	result->refcnt = 1;
 	audit_getname(result);
 
 	return result;
 }
 
-#ifdef CONFIG_AUDITSYSCALL
 void putname(struct filename *name)
 {
-	if (unlikely(!audit_dummy_context()))
-		return audit_putname(name);
-	final_putname(name);
+	BUG_ON(name->refcnt <= 0);
+
+	if (--name->refcnt > 0)
+		return;
+
+	if (name->separate) {
+		__putname(name->name);
+		kfree(name);
+	} else
+		__putname(name);
 }
-#endif
 
 static int check_acl(struct inode *inode, int mask)
 {