fusefrontend_reverse: secure GetAttr against symlink races

...by using the OpenNofollow helper & Fstatat.

Also introduce a helper to convert from unix.Stat_t to
syscall.Stat_t.

Tracking ticket: https://github.com/rfjakob/gocryptfs/issues/165

1 files changed, 28 insertions, 0 deletions

diff --git a/internal/syscallcompat/unix2syscall.go b/internal/syscallcompat/unix2syscall.go
new file mode 100644
index 0000000..3162025
--- /dev/null
+++ b/internal/syscallcompat/unix2syscall.go
@@ -0,0 +1,28 @@
+package syscallcompat
+
+import (
+	"syscall"
+
+	"golang.org/x/sys/unix"
+)
+
+// Unix2syscall converts a unix.Stat_t struct to a syscall.Stat_t struct.
+// A direct cast does not work because the padding is named differently in
+// unix.Stat_t for some reason ("X__unused" in syscall, "_" in unix).
+func Unix2syscall(u unix.Stat_t) syscall.Stat_t {
+	return syscall.Stat_t{
+		Dev:     u.Dev,
+		Ino:     u.Ino,
+		Nlink:   u.Nlink,
+		Mode:    u.Mode,
+		Uid:     u.Uid,
+		Gid:     u.Gid,
+		Rdev:    u.Rdev,
+		Size:    u.Size,
+		Blksize: u.Blksize,
+		Blocks:  u.Blocks,
+		Atim:    syscall.Timespec(u.Atim),
+		Mtim:    syscall.Timespec(u.Mtim),
+		Ctim:    syscall.Timespec(u.Ctim),
+	}
+}