Re: [PATCH v8 2/5] IMA: Define an IMA hook to measure keys

[Eric Snowberg <eric.snowberg@oracle.com>]

> On Nov 18, 2019, at 3:38 PM, Lakshmi Ramasubramanian <nramas@linux.microsoft.com> wrote:
> 
> Measure asymmetric keys used for verifying file signatures,
> certificates, etc.
> 
> This patch defines a new IMA hook namely ima_post_key_create_or_update()
> to measure asymmetric keys.
> 
> The IMA hook is defined in a new file namely ima_asymmetric_keys.c
> which is built only if CONFIG_ASYMMETRIC_PUBLIC_KEY_SUBTYPE is enabled.
> 
> Signed-off-by: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
> Cc: Sasha Levin <sashal@kernel.org>
> Cc: James Morris <jamorris@linux.microsoft.com>
> ---
> security/integrity/ima/Makefile              |  1 +
> security/integrity/ima/ima_asymmetric_keys.c | 51 ++++++++++++++++++++
> 2 files changed, 52 insertions(+)
> create mode 100644 security/integrity/ima/ima_asymmetric_keys.c
> 
> diff --git a/security/integrity/ima/Makefile b/security/integrity/ima/Makefile
> index 31d57cdf2421..207a0a9eb72c 100644
> --- a/security/integrity/ima/Makefile
> +++ b/security/integrity/ima/Makefile
> @@ -12,3 +12,4 @@ ima-$(CONFIG_IMA_APPRAISE) += ima_appraise.o
> ima-$(CONFIG_IMA_APPRAISE_MODSIG) += ima_modsig.o
> ima-$(CONFIG_HAVE_IMA_KEXEC) += ima_kexec.o
> obj-$(CONFIG_IMA_BLACKLIST_KEYRING) += ima_mok.o
> +obj-$(CONFIG_ASYMMETRIC_PUBLIC_KEY_SUBTYPE) += ima_asymmetric_keys.o
> diff --git a/security/integrity/ima/ima_asymmetric_keys.c b/security/integrity/ima/ima_asymmetric_keys.c
> new file mode 100644
> index 000000000000..f6884641a622
> --- /dev/null
> +++ b/security/integrity/ima/ima_asymmetric_keys.c
> @@ -0,0 +1,51 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +/*
> + * Copyright (C) 2019 Microsoft Corporation
> + *
> + * Author: Lakshmi Ramasubramanian (nramas@linux.microsoft.com)
> + *
> + * File: ima_asymmetric_keys.c
> + *       Defines an IMA hook to measure asymmetric keys on key
> + *       create or update.
> + */
> +
> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> +
> +#include <crypto/public_key.h>
> +#include <keys/asymmetric-type.h>
> +#include "ima.h"
> +
> +/**
> + * ima_post_key_create_or_update - measure asymmetric keys
> + * @keyring: keyring to which the key is linked to
> + * @key: created or updated key
> + * @flags: key flags
> + * @create: flag indicating whether the key was created or updated
> + *
> + * Keys can only be measured, not appraised.
> + */
> +void ima_post_key_create_or_update(struct key *keyring, struct key *key,
> +				   unsigned long flags, bool create)
> +{
> +	const struct public_key *pk;
> +
> +	/* Only asymmetric keys are handled by this hook. */
> +	if (key->type != &key_type_asymmetric)
> +		return;
> +
> +	/* Get the public_key of the given asymmetric key to measure. */
> +	pk = key->payload.data[asym_crypto];
> +
> +	/*
> +	 * keyring->description points to the name of the keyring
> +	 * (such as ".builtin_trusted_keys", ".ima", etc.) to
> +	 * which the given key is linked to.
> +	 *
> +	 * The name of the keyring is passed in the "eventname"
> +	 * parameter to process_buffer_measurement() and is set
> +	 * in the "eventname" field in ima_event_data for
> +	 * the key measurement IMA event.
> +	 */
> +	process_buffer_measurement(pk->key, pk->keylen,
> +				   keyring->description, KEY_CHECK, 0);

I’m interested in using this patch series, however I get the following on every boot:

[    1.185105] Loading compiled-in X.509 certificates
[    1.190240] BUG: kernel NULL pointer dereference, address: 0000000000000000
[    1.191835] #PF: supervisor read access in kernel mode
[    1.193041] #PF: error_code(0x0000) - not-present page
[    1.194224] PGD 0 P4D 0
[    1.194832] Oops: 0000 [#1] SMP PTI
[    1.195654] CPU: 1 PID: 1 Comm: swapper/0 Not tainted 5.4.0-rc7.imakeys.rc1.x86_64 #1
[    1.197667] Hardware name: 
[    1.198987] RIP: 0010:ima_match_policy+0x69/0x4e0
[    1.200072] Code: 48 89 45 90 65 48 8b 04 25 28 00 00 00 48 89 45 d0 31 c0 4d 85 ff 74 08 e8 94 14 00 00 49 89 07 48 8b 05 8a 43 7f 01 45 31 e4 <48> 8b 18 48 39 d8 0f 84 25 02 00 00 41 8d 46 f5 45 89 e0 4c 8b 65
[    1.204401] RSP: 0018:ffffb9f30001bac8 EFLAGS: 00010246
[    1.205622] RAX: 0000000000000000 RBX: ffff9e659de81800 RCX: 000000000000000c
[    1.207275] RDX: 0000000000000000 RSI: ffffffff9b13cdf8 RDI: ffffffff9b13cdf8
[    1.208938] RBP: ffffb9f30001bb48 R08: ffffffff9b529200 R09: 0000000000000000
[    1.210560] R10: ffff9e6447d06c00 R11: 0000000082c49530 R12: 0000000000000000
[    1.212279] R13: 0000000000000000 R14: 000000000000000c R15: ffffb9f30001bbb0
[    1.213944] FS:  0000000000000000(0000) GS:ffff9e65b7a80000(0000) knlGS:0000000000000000
[    1.215768] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    1.217114] CR2: 0000000000000000 CR3: 000000014240a001 CR4: 0000000000760ee0
[    1.218734] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[    1.220481] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[    1.222139] PKRU: 55555554
[    1.222749] Call Trace:
[    1.223344]  ? crypto_destroy_tfm+0x5f/0xb0
[    1.224315]  ima_get_action+0x2c/0x30
[    1.225148]  process_buffer_measurement+0x1da/0x230
[    1.226306]  ima_post_key_create_or_update+0x3b/0x40
[    1.227459]  key_create_or_update+0x371/0x5c0
[    1.228494]  load_system_certificate_list+0x99/0xfa
[    1.229588]  ? system_trusted_keyring_init+0xfb/0xfb
[    1.230705]  ? do_early_param+0x95/0x95
[    1.231574]  do_one_initcall+0x4a/0x1fa
[    1.232444]  ? do_early_param+0x95/0x95
[    1.233313]  kernel_init_freeable+0x1c2/0x267
[    1.234300]  ? rest_init+0xb0/0xb0
[    1.235075]  kernel_init+0xe/0x110
[    1.235842]  ret_from_fork+0x24/0x50
[    1.236659] Modules linked in:
[    1.237358] CR2: 0000000000000000
[    1.238112] ---[ end trace 163f3f61dfaef23f ]—


I believe this is because ima_rules used within ima_match_policy has not been initialized yet, when process_buffer_measurement is called above.