From 8f76d1ea0a63f546ad09fa70be1ed7b6a7d29fe6 Mon Sep 17 00:00:00 2001
From: Jakob Unterwurzacher
Date: Fri, 2 Jun 2023 14:24:44 +0200
Subject: fusefrontend: sharedstorage: use byte-range lock on file header
 creation

Multiple host writing to the same empty file at the same time
could have overwritten each other's newly created file header,
leading to data corruption.

Fix the race by placing a byte-range lock on the file when
creating the file header.
---
 internal/syscallcompat/sys_darwin.go | 4 ++++
 internal/syscallcompat/sys_linux.go  | 1 +
 2 files changed, 5 insertions(+)

(limited to 'internal/syscallcompat')

diff --git a/internal/syscallcompat/sys_darwin.go b/internal/syscallcompat/sys_darwin.go
index 06f09f0..b13b6a5 100644
--- a/internal/syscallcompat/sys_darwin.go
+++ b/internal/syscallcompat/sys_darwin.go
@@ -27,6 +27,10 @@ const (
 	RENAME_EXCHANGE  = 2
 	RENAME_WHITEOUT  = 4
 
+	// F_OFD_SETLKW only exists on Linux. On Darwin, fall back to F_SETLKW as a
+	// flawed replacement.
+	F_OFD_SETLKW = unix.F_SETLKW
+
 	// KAUTH_UID_NONE and KAUTH_GID_NONE are special values to
 	// revert permissions to the process credentials.
 	KAUTH_UID_NONE = ^uint32(0) - 100
diff --git a/internal/syscallcompat/sys_linux.go b/internal/syscallcompat/sys_linux.go
index a64b27e..3714b75 100644
--- a/internal/syscallcompat/sys_linux.go
+++ b/internal/syscallcompat/sys_linux.go
@@ -32,6 +32,7 @@ const (
 	RENAME_NOREPLACE = unix.RENAME_NOREPLACE
 	RENAME_WHITEOUT  = unix.RENAME_WHITEOUT
 	RENAME_EXCHANGE  = unix.RENAME_EXCHANGE
+	F_OFD_SETLKW     = unix.F_OFD_SETLKW
 )
 
 var preallocWarn sync.Once
-- 
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