crypto: Add a function to check for label and subsystem validity #1133

vojtechtrefny · 2025-10-09T14:33:02Z

cryptsetup recently started imposing some limits on label and subsystem lenght so we should add a function for the users to be able to check if their label and subsystem are valid. This is similar to existing FS plugin functions.

See also: https://gitlab.com/cryptsetup/cryptsetup/-/merge_requests/841

gemini-code-assist · 2025-10-09T14:33:17Z

Summary of Changes

Hello @vojtechtrefny, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request integrates a new validation utility, bd_crypto_luks_check_label, into the crypto plugin. This function allows users to verify that their LUKS2 labels and subsystems conform to the recently introduced 48-character length limit imposed by cryptsetup, thereby preventing potential issues during cryptographic device setup or modification.

Highlights

New Validation Function: A new function, bd_crypto_luks_check_label, has been introduced to validate LUKS2 labels and subsystems.
Length Enforcement: This function enforces a maximum length of 48 characters for LUKS2 labels and subsystems, aligning with recent cryptsetup requirements.
Proactive User Checks: The addition provides users with a dedicated utility to proactively check the validity of their labels and subsystems before attempting to set them, similar to existing filesystem plugin functions.
Comprehensive Testing: New unit tests have been added to tests/crypto_test.py to ensure the correct behavior and error handling of the new validation function, covering both valid and invalid input lengths.

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gemini-code-assist

Code Review

This pull request introduces a new function, bd_crypto_luks_check_label, to validate the length of LUKS labels and subsystems, which is a valuable addition. However, the implementation contains a correctness issue regarding the maximum allowed length. The check incorrectly permits a length of 48 characters, whereas the limit should be 47 to account for the null terminator in the 48-byte buffer. This error also impacts the accompanying tests, which do not verify the correct boundary condition. I have provided specific suggestions to address these issues in both the function implementation and the tests.

gemini-code-assist · 2025-10-09T14:35:34Z

src/plugins/crypto.c

+    if (label && strlen (label) > 48) {
+        g_set_error (error, BD_CRYPTO_ERROR, BD_CRYPTO_ERROR_INVALID_PARAMS,
+                     "Label for LUKS must be at most 48 characters long");
+        return FALSE;
+    }
+
+    if (subsystem && strlen (subsystem) > 48) {
+        g_set_error (error, BD_CRYPTO_ERROR, BD_CRYPTO_ERROR_INVALID_PARAMS,
+                     "Subsystem for LUKS must be at most 48 characters long");
+        return FALSE;
+    }


The maximum length for a LUKS2 label or subsystem is 47 characters, as the on-disk format reserves a 48-byte buffer which must include the NULL terminator. The current implementation incorrectly allows for a length of 48 characters.

The check should be against a maximum length of 47. Please update the length check and the corresponding error message. For better maintainability, consider defining a constant for the maximum length (47) and using it in both the check and the error message.

For reference, see the cryptsetup merge request that introduced this limit: https://gitlab.com/cryptsetup/cryptsetup/-/merge_requests/841. The final implementation there uses >= 48 (which is equivalent to > 47) for the check.

if (label && strlen (label) > 47) { g_set_error (error, BD_CRYPTO_ERROR, BD_CRYPTO_ERROR_INVALID_PARAMS, "Label for LUKS must be at most 47 characters long"); return FALSE; } if (subsystem && strlen (subsystem) > 47) { g_set_error (error, BD_CRYPTO_ERROR, BD_CRYPTO_ERROR_INVALID_PARAMS, "Subsystem for LUKS must be at most 47 characters long"); return FALSE; }

Nice catch!

gemini-code-assist · 2025-10-09T14:35:34Z

tests/crypto_test.py

+        with self.assertRaisesRegex(GLib.GError, "Label for LUKS must be at most 48 characters long"):
+            BlockDev.crypto_luks_check_label(label="a" * 49)
+        with self.assertRaisesRegex(GLib.GError, "Subsystem for LUKS must be at most 48 characters long"):
+            BlockDev.crypto_luks_check_label(subsystem="a" * 49)


The test for invalid label/subsystem length should be updated to reflect the correct maximum length of 47 characters. The test should check the boundary condition, i.e., a string of length 48 should be invalid.

Also, the expected error message in assertRaisesRegex needs to be updated to mention '47 characters'.

Suggested change

with self.assertRaisesRegex(GLib.GError, "Label for LUKS must be at most 48 characters long"):

BlockDev.crypto_luks_check_label(label="a" * 49)

with self.assertRaisesRegex(GLib.GError, "Subsystem for LUKS must be at most 48 characters long"):

BlockDev.crypto_luks_check_label(subsystem="a" * 49)

with self.assertRaisesRegex(GLib.GError, "Label for LUKS must be at most 47 characters long"):

BlockDev.crypto_luks_check_label(label="a" * 48)

with self.assertRaisesRegex(GLib.GError, "Subsystem for LUKS must be at most 47 characters long"):

BlockDev.crypto_luks_check_label(subsystem="a" * 48)

vojtechtrefny · 2025-10-09T14:40:20Z

/gemini review

cryptsetup recently started imposing some limits on label and subsystem lenght so we should add a function for the users to be able to check if their label and subsystem are valid. This is similar to existing FS plugin functions. See also: https://gitlab.com/cryptsetup/cryptsetup/-/merge_requests/841

gemini-code-assist

Code Review

This pull request introduces a new function bd_crypto_luks_check_label to validate LUKS2 label and subsystem lengths. The implementation is a good addition, but there's a critical issue with the length validation logic that could lead to a buffer overflow in cryptsetup. The maximum allowed length is 47 characters, not 48. I've provided a suggestion to fix this. Additionally, the corresponding tests should be updated to check for this boundary condition. My review includes comments with detailed explanations and code suggestions for these improvements.

gemini-code-assist · 2025-10-09T15:23:40Z

src/plugins/crypto.c

+gboolean bd_crypto_luks_check_label (const gchar *label, const gchar *subsystem, GError **error) {
+    if (label && strlen (label) > 47) {
+        g_set_error (error, BD_CRYPTO_ERROR, BD_CRYPTO_ERROR_INVALID_PARAMS,
+                     "Label for LUKS must be at most 47 characters long");
+        return FALSE;
+    }
+
+    if (subsystem && strlen (subsystem) > 47) {
+        g_set_error (error, BD_CRYPTO_ERROR, BD_CRYPTO_ERROR_INVALID_PARAMS,
+                     "Subsystem for LUKS must be at most 47 characters long");
+        return FALSE;
+    }
+
+    return TRUE;
+}


The length checks for both label and subsystem are incorrect. According to the cryptsetup source, the on-disk format for these fields is a 48-byte character array, which includes the null terminator. This means the maximum string length is 47 characters.

The current checks (> 48) allow strings of 48 characters, which would lead to a buffer overflow when used by cryptsetup.

The checks should be changed to > 47, and the error messages should be updated to reflect the correct maximum length.

gboolean bd_crypto_luks_check_label (const gchar *label, const gchar *subsystem, GError **error) { if (label && strlen (label) > 47) { g_set_error (error, BD_CRYPTO_ERROR, BD_CRYPTO_ERROR_INVALID_PARAMS, "Label for LUKS must be at most 47 characters long"); return FALSE; } if (subsystem && strlen (subsystem) > 47) { g_set_error (error, BD_CRYPTO_ERROR, BD_CRYPTO_ERROR_INVALID_PARAMS, "Subsystem for LUKS must be at most 47 characters long"); return FALSE; } return TRUE; }

gemini-code-assist · 2025-10-09T15:23:40Z

tests/crypto_test.py

+        with self.assertRaisesRegex(GLib.GError, "Label for LUKS must be at most 47 characters long"):
+            BlockDev.crypto_luks_check_label(label="a" * 48)
+        with self.assertRaisesRegex(GLib.GError, "Subsystem for LUKS must be at most 47 characters long"):
+            BlockDev.crypto_luks_check_label(subsystem="a" * 48)


The tests for the new function are good, but they are missing a check for the boundary condition. A string of length 48 should be invalid.

Please add tests for strings of exactly 48 characters for both label and subsystem to ensure the boundary is handled correctly. These tests should expect a GLib.GError. I've also updated the existing tests to check for the corrected error message.

Suggested change

with self.assertRaisesRegex(GLib.GError, "Label for LUKS must be at most 47 characters long"):

BlockDev.crypto_luks_check_label(label="a" * 48)

with self.assertRaisesRegex(GLib.GError, "Subsystem for LUKS must be at most 47 characters long"):

BlockDev.crypto_luks_check_label(subsystem="a" * 48)

with self.assertRaisesRegex(GLib.GError, "Label for LUKS must be at most 47 characters long"):

BlockDev.crypto_luks_check_label(label="a" * 48)

with self.assertRaisesRegex(GLib.GError, "Label for LUKS must be at most 47 characters long"):

BlockDev.crypto_luks_check_label(label="a" * 49)

with self.assertRaisesRegex(GLib.GError, "Subsystem for LUKS must be at most 47 characters long"):

BlockDev.crypto_luks_check_label(subsystem="a" * 48)

with self.assertRaisesRegex(GLib.GError, "Subsystem for LUKS must be at most 47 characters long"):

BlockDev.crypto_luks_check_label(subsystem="a" * 49)

gemini-code-assist bot reviewed Oct 9, 2025

View reviewed changes

vojtechtrefny force-pushed the master_crypto-check-label branch from bf090bf to 26d8ed0 Compare October 9, 2025 15:22

gemini-code-assist bot reviewed Oct 9, 2025

View reviewed changes

vojtechtrefny force-pushed the master_crypto-check-label branch from 26d8ed0 to 115597a Compare October 9, 2025 15:27

tbzatek approved these changes Oct 9, 2025

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vojtechtrefny merged commit 632959e into storaged-project:master Oct 10, 2025
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crypto: Add a function to check for label and subsystem validity #1133

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