From 339536de5eefe782813aabae4aeeb312b3c4dde7 Mon Sep 17 00:00:00 2001
From: Kevin Krakauer <krakauer@google.com>
Date: Thu, 14 Nov 2019 15:55:07 -0800
Subject: Check that a file is a regular file with open(O_TRUNC).

It was possible to panic the sentry by opening a cache revalidating folder with
O_TRUNC|O_CREAT.

Avoids breaking php tests.

PiperOrigin-RevId: 280533213
---
 pkg/sentry/fs/inode.go                | 4 ++++
 pkg/sentry/fs/tty/master.go           | 1 +
 pkg/sentry/fs/tty/slave.go            | 1 +
 pkg/sentry/syscalls/linux/sys_file.go | 9 +++++----
 4 files changed, 11 insertions(+), 4 deletions(-)

(limited to 'pkg/sentry')

diff --git a/pkg/sentry/fs/inode.go b/pkg/sentry/fs/inode.go
index f4ddfa406..2d43dff1d 100644
--- a/pkg/sentry/fs/inode.go
+++ b/pkg/sentry/fs/inode.go
@@ -344,6 +344,10 @@ func (i *Inode) SetTimestamps(ctx context.Context, d *Dirent, ts TimeSpec) error
 
 // Truncate calls i.InodeOperations.Truncate with i as the Inode.
 func (i *Inode) Truncate(ctx context.Context, d *Dirent, size int64) error {
+	if IsDir(i.StableAttr) {
+		return syserror.EISDIR
+	}
+
 	if i.overlay != nil {
 		return overlayTruncate(ctx, i.overlay, d, size)
 	}
diff --git a/pkg/sentry/fs/tty/master.go b/pkg/sentry/fs/tty/master.go
index 19b7557d5..bc56be696 100644
--- a/pkg/sentry/fs/tty/master.go
+++ b/pkg/sentry/fs/tty/master.go
@@ -32,6 +32,7 @@ import (
 // +stateify savable
 type masterInodeOperations struct {
 	fsutil.SimpleFileInode
+	fsutil.InodeNoopTruncate
 
 	// d is the containing dir.
 	d *dirInodeOperations
diff --git a/pkg/sentry/fs/tty/slave.go b/pkg/sentry/fs/tty/slave.go
index 944c4ada1..4cbea0367 100644
--- a/pkg/sentry/fs/tty/slave.go
+++ b/pkg/sentry/fs/tty/slave.go
@@ -31,6 +31,7 @@ import (
 // +stateify savable
 type slaveInodeOperations struct {
 	fsutil.SimpleFileInode
+	fsutil.InodeNoopTruncate
 
 	// d is the containing dir.
 	d *dirInodeOperations
diff --git a/pkg/sentry/syscalls/linux/sys_file.go b/pkg/sentry/syscalls/linux/sys_file.go
index b9a8e3e21..167c2b60b 100644
--- a/pkg/sentry/syscalls/linux/sys_file.go
+++ b/pkg/sentry/syscalls/linux/sys_file.go
@@ -169,10 +169,11 @@ func openAt(t *kernel.Task, dirFD int32, addr usermem.Addr, flags uint) (fd uint
 			if dirPath {
 				return syserror.ENOTDIR
 			}
-			if flags&linux.O_TRUNC != 0 {
-				if err := d.Inode.Truncate(t, d, 0); err != nil {
-					return err
-				}
+		}
+
+		if flags&linux.O_TRUNC != 0 {
+			if err := d.Inode.Truncate(t, d, 0); err != nil {
+				return err
 			}
 		}
 
-- 
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