util: Limit cryptsetup PBKDF memory usage

By default, `cryptsetup luksFormat` uses Argon2i as Password-Based Key
Derivation Function (PBKDF), which not only has a CPU cost, but also a memory
cost (to make brute-force attacks harder).

The memory cost is based on the available system memory by default, which in
the context of Ceph CSI can be a problem for two reasons:

1. Pods can have a memory limit (much lower that the memory available on the
   node, usually) which isn't taken into account by `cryptsetup`, so it can get
   OOM-killed when formating a new volume;
2. The amount of memory that was used during `cryptsetup luksFormat` will then
   be needed for `cryptsetup luksOpen`, so if the volume was formated on a node
   with a lot of memory, but then needs to be opened on a different node with
   less memory, `cryptsetup` will get OOM-killed.

This commit sets the PBKDF memory limit to a fixed value to ensure consistent
memory usage regardless of the specifications of the nodes where the volume
happens to be formatted in the first place.

The limit is set to a relatively low value (32 MiB) so that the `csi-rbdplugin`
container in the `nodeplugin` pod doesn't require an extravagantly high memory
limit in order to format/open volumes (particularly with operations happening
in parallel), while at the same time not being so low as to render it
completely pointless.

Signed-off-by: Benoît Knecht <bknecht@protonmail.ch>

internal/util/cryptsetup.go

@@ -20,9 +20,13 @@ import (
 	"bytes"
 	"fmt"
 	"os/exec"
+	"strconv"
 	"strings"
 )
 
+// Limit memory used by Argon2i PBKDF to 32 MiB.
+const cryptsetupPBKDFMemoryLimit = 32 << 10 // 32768 KiB
+
 // LuksFormat sets up volume as an encrypted LUKS partition.
 func LuksFormat(devicePath, passphrase string) (string, string, error) {
 	return execCryptsetupCommand(
@@ -33,6 +37,8 @@ func LuksFormat(devicePath, passphrase string) (string, string, error) {
 		"luks2",
 		"--hash",
 		"sha256",
+		"--pbkdf-memory",
+		strconv.Itoa(cryptsetupPBKDFMemoryLimit),
 		devicePath,
 		"-d",
 		"/dev/stdin")