From 8650614c32c4dc5e8754b7bf4c84278551cff419 Mon Sep 17 00:00:00 2001
From: Rahat Mahmood <rahat@google.com>
Date: Fri, 12 Nov 2021 17:31:23 -0800
Subject: [PATCH] Shift buffer correctly when unmarshalling FUSE dirents.

PiperOrigin-RevId: 409547679
---
 pkg/abi/linux/fuse.go | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/pkg/abi/linux/fuse.go b/pkg/abi/linux/fuse.go
index 1112dadd6..0147077a3 100644
--- a/pkg/abi/linux/fuse.go
+++ b/pkg/abi/linux/fuse.go
@@ -782,21 +782,31 @@ func (r *FUSEDirent) SizeBytes() int {
 	return (dataSize + (FUSE_DIRENT_ALIGN - 1)) & ^(FUSE_DIRENT_ALIGN - 1)
 }
 
+// shiftNextDirent advances buf to the start of the next dirent, per
+// FUSE ABI. buf should begin at the start of a dirent.
+func (r *FUSEDirent) shiftNextDirent(buf []byte) []byte {
+	nextOff := r.SizeBytes()
+	if nextOff > len(buf) { // Handle overflow.
+		return buf[len(buf):]
+	}
+	return buf[nextOff:]
+}
+
 // UnmarshalBytes deserializes FUSEDirent from the src buffer.
 func (r *FUSEDirent) UnmarshalBytes(src []byte) []byte {
-	src = r.Meta.UnmarshalBytes(src)
+	srcP := r.Meta.UnmarshalBytes(src)
 
 	if r.Meta.NameLen > FUSE_NAME_MAX {
 		// The name is too long and therefore invalid. We don't
 		// need to unmarshal the name since it'll be thrown away.
-		return src
+		return r.shiftNextDirent(src)
 	}
 
 	buf := make([]byte, r.Meta.NameLen)
 	name := primitive.ByteSlice(buf)
-	name.UnmarshalBytes(src[:r.Meta.NameLen])
+	name.UnmarshalBytes(srcP[:r.Meta.NameLen])
 	r.Name = string(name)
-	return src[r.Meta.NameLen:]
+	return r.shiftNextDirent(src)
 }
 
 // FATTR_* consts are the attribute flags defined in include/uapi/linux/fuse.h.