From 36134667b289a3e96e90abf9e18e1c2137069d6b Mon Sep 17 00:00:00 2001
From: Dean Deng <deandeng@google.com>
Date: Wed, 12 Aug 2020 18:09:34 -0700
Subject: Add reference leak checking to vfs2 tmpfs.inode.

Updates #1486.

PiperOrigin-RevId: 326354750
---
 pkg/sentry/fsimpl/tmpfs/BUILD    | 13 +++++++++++++
 pkg/sentry/fsimpl/tmpfs/tmpfs.go | 27 ++++++---------------------
 2 files changed, 19 insertions(+), 21 deletions(-)

(limited to 'pkg/sentry/fsimpl')

diff --git a/pkg/sentry/fsimpl/tmpfs/BUILD b/pkg/sentry/fsimpl/tmpfs/BUILD
index e73732a6b..5cd428d64 100644
--- a/pkg/sentry/fsimpl/tmpfs/BUILD
+++ b/pkg/sentry/fsimpl/tmpfs/BUILD
@@ -26,6 +26,17 @@ go_template_instance(
     },
 )
 
+go_template_instance(
+    name = "inode_refs",
+    out = "inode_refs.go",
+    package = "tmpfs",
+    prefix = "inode",
+    template = "//pkg/refs_vfs2:refs_template",
+    types = {
+        "T": "inode",
+    },
+)
+
 go_library(
     name = "tmpfs",
     srcs = [
@@ -34,6 +45,7 @@ go_library(
         "directory.go",
         "filesystem.go",
         "fstree.go",
+        "inode_refs.go",
         "named_pipe.go",
         "regular_file.go",
         "socket_file.go",
@@ -47,6 +59,7 @@ go_library(
         "//pkg/context",
         "//pkg/fspath",
         "//pkg/log",
+        "//pkg/refs",
         "//pkg/safemem",
         "//pkg/sentry/arch",
         "//pkg/sentry/fs",
diff --git a/pkg/sentry/fsimpl/tmpfs/tmpfs.go b/pkg/sentry/fsimpl/tmpfs/tmpfs.go
index 4681a2f52..de2af6d01 100644
--- a/pkg/sentry/fsimpl/tmpfs/tmpfs.go
+++ b/pkg/sentry/fsimpl/tmpfs/tmpfs.go
@@ -285,13 +285,10 @@ type inode struct {
 	// fs is the owning filesystem. fs is immutable.
 	fs *filesystem
 
-	// refs is a reference count. refs is accessed using atomic memory
-	// operations.
-	//
 	// A reference is held on all inodes as long as they are reachable in the
 	// filesystem tree, i.e. nlink is nonzero. This reference is dropped when
 	// nlink reaches 0.
-	refs int64
+	refs inodeRefs
 
 	// xattrs implements extended attributes.
 	//
@@ -327,7 +324,6 @@ func (i *inode) init(impl interface{}, fs *filesystem, kuid auth.KUID, kgid auth
 		panic("file type is required in FileMode")
 	}
 	i.fs = fs
-	i.refs = 1
 	i.mode = uint32(mode)
 	i.uid = uint32(kuid)
 	i.gid = uint32(kgid)
@@ -339,6 +335,7 @@ func (i *inode) init(impl interface{}, fs *filesystem, kuid auth.KUID, kgid auth
 	i.mtime = now
 	// i.nlink initialized by caller
 	i.impl = impl
+	i.refs.EnableLeakCheck()
 }
 
 // incLinksLocked increments i's link count.
@@ -369,25 +366,15 @@ func (i *inode) decLinksLocked(ctx context.Context) {
 }
 
 func (i *inode) incRef() {
-	if atomic.AddInt64(&i.refs, 1) <= 1 {
-		panic("tmpfs.inode.incRef() called without holding a reference")
-	}
+	i.refs.IncRef()
 }
 
 func (i *inode) tryIncRef() bool {
-	for {
-		refs := atomic.LoadInt64(&i.refs)
-		if refs == 0 {
-			return false
-		}
-		if atomic.CompareAndSwapInt64(&i.refs, refs, refs+1) {
-			return true
-		}
-	}
+	return i.refs.TryIncRef()
 }
 
 func (i *inode) decRef(ctx context.Context) {
-	if refs := atomic.AddInt64(&i.refs, -1); refs == 0 {
+	i.refs.DecRef(func() {
 		i.watches.HandleDeletion(ctx)
 		if regFile, ok := i.impl.(*regularFile); ok {
 			// Release memory used by regFile to store data. Since regFile is
@@ -395,9 +382,7 @@ func (i *inode) decRef(ctx context.Context) {
 			// metadata.
 			regFile.data.DropAll(regFile.memFile)
 		}
-	} else if refs < 0 {
-		panic("tmpfs.inode.decRef() called without holding a reference")
-	}
+	})
 }
 
 func (i *inode) checkPermissions(creds *auth.Credentials, ats vfs.AccessTypes) error {
-- 
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