From efc280330c68dc5cbf605921f6c840a54d5841bb Mon Sep 17 00:00:00 2001
From: Sebastian Lackner
Date: Sat, 12 Jan 2019 21:22:52 +0100
Subject: fusefrontend: -allow_other: Use SymlinkatUser in Symlink FUSE call.

Instead of manually adjusting the user after creating the symlink,
adjust effective permissions and let the kernel deal with it.

Related to https://github.com/rfjakob/gocryptfs/issues/338.
---
 internal/syscallcompat/sys_linux.go | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

(limited to 'internal/syscallcompat/sys_linux.go')

diff --git a/internal/syscallcompat/sys_linux.go b/internal/syscallcompat/sys_linux.go
index cf747b1..6f2a70d 100644
--- a/internal/syscallcompat/sys_linux.go
+++ b/internal/syscallcompat/sys_linux.go
@@ -197,6 +197,28 @@ func Symlinkat(oldpath string, newdirfd int, newpath string) (err error) {
 	return unix.Symlinkat(oldpath, newdirfd, newpath)
 }
 
+// SymlinkatUser runs the Symlinkat syscall in the context of a different user.
+func SymlinkatUser(oldpath string, newdirfd int, newpath string, context *fuse.Context) (err error) {
+	if context != nil {
+		runtime.LockOSThread()
+		defer runtime.UnlockOSThread()
+
+		err = syscall.Setregid(-1, int(context.Owner.Gid))
+		if err != nil {
+			return err
+		}
+		defer syscall.Setregid(-1, 0)
+
+		err = syscall.Setreuid(-1, int(context.Owner.Uid))
+		if err != nil {
+			return err
+		}
+		defer syscall.Setreuid(-1, 0)
+	}
+
+	return Symlinkat(oldpath, newdirfd, newpath)
+}
+
 // Mkdirat syscall.
 func Mkdirat(dirfd int, path string, mode uint32) (err error) {
 	return syscall.Mkdirat(dirfd, path, mode)
-- 
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