grub2/0002-Requiring-authentication-after-tpm-unlock-for-CLI-ac.patch

From 0ed98269c5631c4d094b2cee81ce385687803730 Mon Sep 17 00:00:00 2001
From: Michael Chang <mchang@suse.com>
Date: Thu, 29 Aug 2024 13:27:30 +0800
Subject: [PATCH 2/2] Requiring authentication after tpm unlock for CLI access

The GRUB may use TPM to verify the integrity of boot components and the
result can determine whether a previously sealed key can be released. If
everything checks out, showing nothing has been tampered with, the key
is released and GRUB unlocks the encrypted root partition for the next
stage of booting.

However, the liberal Command Line Interface (CLI) can be misused by
anyone in this case to access files in the encrypted partition one way
or another. Despite efforts to keep the CLI secure by preventing utility
command output from leaking file content, many techniques in the wild
could still be used to exploit the CLI, enabling attacks or learning
methods to attack. It's nearly impossible to account for all scenarios
where a hack could be applied.

Therefore, to mitigate potential misuse of the CLI after the root device
has been successfully unlocked via TPM, the user should be required to
authenticate using the LUKS password. This added layer of security
ensures that only authorized users can access the CLI reducing the risk
of exploitation or unauthorized access to the encrypted partition.

Fixes: CVE-2024-49504

Signed-off-by: Michael Chang <mchang@suse.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
---
 grub-core/disk/cryptodisk.c   | 84 +++++++++++++++++++++++++++++++++++
 grub-core/kern/main.c         | 12 +++++
 grub-core/normal/auth.c       | 30 +++++++++++++
 grub-core/normal/main.c       |  4 ++
 grub-core/normal/menu_entry.c |  4 ++
 include/grub/auth.h           |  1 +
 include/grub/cryptodisk.h     |  3 ++
 include/grub/misc.h           |  2 +
 8 files changed, 140 insertions(+)

diff --git a/grub-core/disk/cryptodisk.c b/grub-core/disk/cryptodisk.c
index babc94868d..21bf22ead1 100644
--- a/grub-core/disk/cryptodisk.c
+++ b/grub-core/disk/cryptodisk.c
@@ -1188,6 +1188,7 @@ grub_cryptodisk_scan_device_real (const char *name,
 	        goto error;
 #ifndef GRUB_UTIL
 	      is_tpmkey = 1;
+	      grub_cli_set_auth_needed ();
 #endif
 	      goto cleanup;
 	    }
@@ -1706,6 +1707,89 @@ luks_script_get (grub_size_t *sz)
   return ret;
 }
 
+#ifdef GRUB_MACHINE_EFI
+grub_err_t
+grub_cryptodisk_challenge_password (void)
+{
+  grub_cryptodisk_t cr_dev;
+
+  for (cr_dev = cryptodisk_list; cr_dev != NULL; cr_dev = cr_dev->next)
+    {
+      grub_cryptodisk_dev_t cr;
+      grub_disk_t source = NULL;
+      grub_err_t ret = GRUB_ERR_NONE;
+      grub_cryptodisk_t dev = NULL;
+      char *part = NULL;
+      struct grub_cryptomount_args cargs = {0};
+
+      cargs.check_boot = 0;
+      cargs.search_uuid = cr_dev->uuid;
+
+      source = grub_disk_open (cr_dev->source);
+
+      if (source == NULL)
+	{
+	  ret = grub_errno;
+	  goto error_out;
+	}
+
+      FOR_CRYPTODISK_DEVS (cr)
+      {
+	dev = cr->scan (source, &cargs);
+	if (grub_errno)
+	  {
+	    ret = grub_errno;
+	    goto error_out;
+	  }
+	if (dev == NULL)
+	  continue;
+	break;
+      }
+
+      if (dev == NULL)
+	{
+	  ret = grub_error (GRUB_ERR_BAD_MODULE, "no cryptodisk module can handle this device");
+	  goto error_out;
+	}
+
+      part = grub_partition_get_name (source->partition);
+      grub_printf_ (N_("Enter passphrase for %s%s%s (%s): "), source->name,
+		    source->partition != NULL ? "," : "",
+		    part != NULL ? part : N_("UNKNOWN"), cr_dev->uuid);
+      grub_free (part);
+
+      cargs.key_data = grub_malloc (GRUB_CRYPTODISK_MAX_PASSPHRASE);
+      if (cargs.key_data == NULL)
+	{
+	  ret = grub_errno;
+	  goto error_out;
+	}
+
+      if (!grub_password_get ((char *) cargs.key_data, GRUB_CRYPTODISK_MAX_PASSPHRASE))
+	{
+	  ret = grub_error (GRUB_ERR_BAD_ARGUMENT, "passphrase not supplied");
+	  goto error_out;
+	}
+      cargs.key_len = grub_strlen ((char *) cargs.key_data);
+      ret = cr->recover_key (source, dev, &cargs);
+
+ error_out:
+      grub_disk_close (source);
+      if (dev != NULL)
+	cryptodisk_close (dev);
+      if (cargs.key_data)
+	{
+	  grub_memset (cargs.key_data, 0, cargs.key_len);
+	  grub_free (cargs.key_data);
+	}
+
+      return ret;
+    }
+
+  return GRUB_ERR_NONE;
+}
+#endif /* GRUB_MACHINE_EFI */
+
 struct grub_procfs_entry luks_script =
 {
   .name = "luks_script",
diff --git a/grub-core/kern/main.c b/grub-core/kern/main.c
index 07b6940d2e..ef3b3756de 100644
--- a/grub-core/kern/main.c
+++ b/grub-core/kern/main.c
@@ -37,6 +37,7 @@
 #endif
 
 static bool cli_disabled = false;
+static bool cli_need_auth = false;
 
 grub_addr_t
 grub_modules_get_end (void)
@@ -246,6 +247,17 @@ grub_is_cli_disabled (void)
   return cli_disabled;
 }
 
+bool
+grub_is_cli_need_auth (void)
+{
+  return cli_need_auth;
+}
+
+void grub_cli_set_auth_needed (void)
+{
+  cli_need_auth = true;
+}
+
 static void
 check_is_cli_disabled (void)
 {
diff --git a/grub-core/normal/auth.c b/grub-core/normal/auth.c
index d940201866..2931ba604a 100644
--- a/grub-core/normal/auth.c
+++ b/grub-core/normal/auth.c
@@ -25,6 +25,10 @@
 #include <grub/time.h>
 #include <grub/i18n.h>
 
+#ifdef GRUB_MACHINE_EFI
+#include <grub/cryptodisk.h>
+#endif
+
 struct grub_auth_user
 {
   struct grub_auth_user *next;
@@ -200,6 +204,32 @@ grub_username_get (char buf[], unsigned buf_size)
   return (key != GRUB_TERM_ESC);
 }
 
+grub_err_t
+grub_auth_check_cli_access (void)
+{
+  if (grub_is_cli_need_auth () == true)
+    {
+#ifdef GRUB_MACHINE_EFI
+      static bool authenticated = false;
+
+      if (authenticated == false)
+	{
+	  grub_err_t ret;
+
+	  ret = grub_cryptodisk_challenge_password ();
+	  if (ret == GRUB_ERR_NONE)
+	    authenticated = true;
+	  return ret;
+	}
+      return GRUB_ERR_NONE;
+#else
+      return GRUB_ACCESS_DENIED;
+#endif
+    }
+    
+  return GRUB_ERR_NONE;
+}
+
 grub_err_t
 grub_auth_check_authentication (const char *userlist)
 {
diff --git a/grub-core/normal/main.c b/grub-core/normal/main.c
index 8e58ced679..b08fd6977d 100644
--- a/grub-core/normal/main.c
+++ b/grub-core/normal/main.c
@@ -560,9 +560,13 @@ grub_cmdline_run (int nested, int force_auth)
     }
   while (err && force_auth);
 
+  if (err == GRUB_ERR_NONE)
+    err = grub_auth_check_cli_access ();
+
   if (err)
     {
       grub_print_error ();
+      grub_wait_after_message ();
       grub_errno = GRUB_ERR_NONE;
       return;
     }
diff --git a/grub-core/normal/menu_entry.c b/grub-core/normal/menu_entry.c
index e5ba91ea4d..06682a396d 100644
--- a/grub-core/normal/menu_entry.c
+++ b/grub-core/normal/menu_entry.c
@@ -1256,9 +1256,13 @@ grub_menu_entry_run (grub_menu_entry_t entry)
 
   err = grub_auth_check_authentication (NULL);
 
+  if (err == GRUB_ERR_NONE)
+    err = grub_auth_check_cli_access ();
+
   if (err)
     {
       grub_print_error ();
+      grub_wait_after_message ();
       grub_errno = GRUB_ERR_NONE;
       return;
     }
diff --git a/include/grub/auth.h b/include/grub/auth.h
index 7473344517..21d5190f04 100644
--- a/include/grub/auth.h
+++ b/include/grub/auth.h
@@ -33,5 +33,6 @@ grub_err_t grub_auth_unregister_authentication (const char *user);
 grub_err_t grub_auth_authenticate (const char *user);
 grub_err_t grub_auth_deauthenticate (const char *user);
 grub_err_t grub_auth_check_authentication (const char *userlist);
+grub_err_t grub_auth_check_cli_access (void);
 
 #endif /* ! GRUB_AUTH_HEADER */
diff --git a/include/grub/cryptodisk.h b/include/grub/cryptodisk.h
index 0b41e249e8..b3291519b1 100644
--- a/include/grub/cryptodisk.h
+++ b/include/grub/cryptodisk.h
@@ -203,4 +203,7 @@ grub_util_get_geli_uuid (const char *dev);
 grub_cryptodisk_t grub_cryptodisk_get_by_uuid (const char *uuid);
 grub_cryptodisk_t grub_cryptodisk_get_by_source_disk (grub_disk_t disk);
 
+#ifdef GRUB_MACHINE_EFI
+grub_err_t grub_cryptodisk_challenge_password (void);
+#endif
 #endif
diff --git a/include/grub/misc.h b/include/grub/misc.h
index 1578f36c3c..6e94d18f5a 100644
--- a/include/grub/misc.h
+++ b/include/grub/misc.h
@@ -392,6 +392,8 @@ grub_uint64_t EXPORT_FUNC(grub_divmod64) (grub_uint64_t n,
 					  grub_uint64_t *r);
 
 extern bool EXPORT_FUNC(grub_is_cli_disabled) (void);
+extern bool EXPORT_FUNC(grub_is_cli_need_auth) (void);
+extern void EXPORT_FUNC(grub_cli_set_auth_needed) (void);
 
 /* Must match softdiv group in gentpl.py.  */
 #if !defined(GRUB_MACHINE_EMU) && (defined(__arm__) || defined(__ia64__) || \
-- 
2.47.1