RE: [PATCH v2 3/3] ima: Add digest and digest_len params to the functions to measure a buffer

Roberto Sassu
2021-07-02T10:54:11Z

> From: Lakshmi Ramasubramanian [mailto:nramas@linux.microsoft.com]
> Sent: Thursday, July 1, 2021 7:27 PM
> On 7/1/2021 5:55 AM, Roberto Sassu wrote:
>
> Hi Roberto,
>
> > This patch adds the 'digest' and 'digest_len' parameters to
> > ima_measure_critical_data() and process_buffer_measurement(), so that
> > callers can get the digest of the passed buffer.
> >
> > These functions calculate the digest even if there is no suitable rule in
> > the IMA policy and, in this case, they simply return 1 before generating a
> > new measurement entry.
> >
>
> > diff --git a/security/integrity/ima/ima_main.c
> b/security/integrity/ima/ima_main.c
> > index 3386e7436440..b4b1dc25e4fb 100644
> > --- a/security/integrity/ima/ima_main.c
> > +++ b/security/integrity/ima/ima_main.c
> > @@ -838,17 +838,20 @@ int ima_post_load_data(char *buf, loff_t size,
> > * @pcr: pcr to extend the measurement
> > * @func_data: func specific data, may be NULL
> > * @buf_hash: measure buffer data hash
> > + * @digest: buffer digest will be written to
> > + * @digest_len: buffer length
> > *
> > * Based on policy, either the buffer data or buffer data hash is measured
> > *
> > - * Return: 0 if the buffer has been successfully measured, a negative value
> > - * otherwise.
> > + * Return: 0 if the buffer has been successfully measured, 1 if the digest
> > + * has been written to the passed location but not added to a measurement
> entry,
> > + * a negative value otherwise.
> > */
> > int process_buffer_measurement(struct user_namespace *mnt_userns,
> > struct inode *inode, const void *buf, int size,
> > const char *eventname, enum ima_hooks func,
> > int pcr, const char *func_data,
> > - bool buf_hash)
> > + bool buf_hash, u8 *digest, size_t digest_len)
> > {
> > int ret = 0;
> > const char *audit_cause = "ENOMEM";
> > @@ -869,7 +872,10 @@ int process_buffer_measurement(struct
> user_namespace *mnt_userns,
> > int action = 0;
> > u32 secid;
> >
> > - if (!ima_policy_flag)
> > + if (digest && digest_len < digest_hash_len)
> > + return -EINVAL;
> > +
> > + if (!ima_policy_flag && !digest)
> > return -ENOENT;
>
> Just wanted to check if you have verified this scenario:
>
> If ima_policy_flag is 0, the in-memory ima policy data is not yet
> initialized. In this case calling ima_get_action() will cause kernel
> panic (NULL exception).
>
> Please verify the above issue doesn't exist if the caller passes
> non-NULL digest and ima_policy_flag is 0 (ima policy is not initialized).

Yes, it is fixed with commit 067a436b1b0aa.

Thanks

Roberto

HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063
Managing Director: Li Peng, Li Jian, Shi Yanli

> thanks,
> -lakshmi
>
> >
> > template = ima_template_desc_buf();
> > @@ -891,7 +897,7 @@ int process_buffer_measurement(struct
> user_namespace *mnt_userns,
> > action = ima_get_action(mnt_userns, inode, current_cred(),
> > secid, 0, func, &pcr, &template,
> > func_data);
> > - if (!(action & IMA_MEASURE))
> > + if (!(action & IMA_MEASURE) && !digest)
> > return -ENOENT;
> > }
> >
> > @@ -922,6 +928,12 @@ int process_buffer_measurement(struct
> user_namespace *mnt_userns,
> > event_data.buf_len = digest_hash_len;
> > }
> >
> > + if (digest)
> > + memcpy(digest, iint.ima_hash->digest, digest_hash_len);
> > +
> > + if (!ima_policy_flag || (func && !(action & IMA_MEASURE)))
> > + return 1;
> > +
> > ret = ima_alloc_init_template(&event_data, &entry, template);
> > if (ret < 0) {
> > audit_cause = "alloc_entry";
> > @@ -966,7 +978,7 @@ void ima_kexec_cmdline(int kernel_fd, const void
> *buf, int size)
> > ret = process_buffer_measurement(file_mnt_user_ns(f.file),
> > file_inode(f.file), buf, size,
> > "kexec-cmdline", KEXEC_CMDLINE, 0,
> > - NULL, false);
> > + NULL, false, NULL, 0);
> > fdput(f);
> > }
> >
> > @@ -977,26 +989,30 @@ void ima_kexec_cmdline(int kernel_fd, const void
> *buf, int size)
> > * @buf: pointer to buffer data
> > * @buf_len: length of buffer data (in bytes)
> > * @hash: measure buffer data hash
> > + * @digest: buffer digest will be written to
> > + * @digest_len: buffer length
> > *
> > * Measure data critical to the integrity of the kernel into the IMA log
> > * and extend the pcr. Examples of critical data could be various data
> > * structures, policies, and states stored in kernel memory that can
> > * impact the integrity of the system.
> > *
> > - * Return: 0 if the buffer has been successfully measured, a negative value
> > - * otherwise.
> > + * Return: 0 if the buffer has been successfully measured, 1 if the digest
> > + * has been written to the passed location but not added to a measurement
> entry,
> > + * a negative value otherwise.
> > */
> > int ima_measure_critical_data(const char *event_label,
> > const char *event_name,
> > const void *buf, size_t buf_len,
> > - bool hash)
> > + bool hash, u8 *digest, size_t digest_len)
> > {
> > if (!event_name || !event_label || !buf || !buf_len)
> > return -ENOPARAM;
> >
> > return process_buffer_measurement(&init_user_ns, NULL, buf,
> buf_len,
> > event_name, CRITICAL_DATA, 0,
> > - event_label, hash);
> > + event_label, hash, digest,
> > + digest_len);
> > }
> >
> > static int __init init_ima(void)
> > diff --git a/security/integrity/ima/ima_queue_keys.c
> b/security/integrity/ima/ima_queue_keys.c
> > index e3047ce64f39..b02b061c5fac 100644
> > --- a/security/integrity/ima/ima_queue_keys.c
> > +++ b/security/integrity/ima/ima_queue_keys.c
> > @@ -166,7 +166,7 @@ void ima_process_queued_keys(void)
> > entry-
> >keyring_name,
> > KEY_CHECK, 0,
> > entry-
> >keyring_name,
> > - false);
> > + false, NULL, 0);
> > list_del(&entry->list);
> > ima_free_key_entry(entry);
> > }
> > diff --git a/security/selinux/ima.c b/security/selinux/ima.c
> > index 4db9fa211638..d5d7b3ca9651 100644
> > --- a/security/selinux/ima.c
> > +++ b/security/selinux/ima.c
> > @@ -88,7 +88,7 @@ void selinux_ima_measure_state_locked(struct
> selinux_state *state)
> >
> > measure_rc = ima_measure_critical_data("selinux", "selinux-state",
> > state_str, strlen(state_str),
> > - false);
> > + false, NULL, 0);
> >
> > kfree(state_str);
> >
> > @@ -105,7 +105,8 @@ void selinux_ima_measure_state_locked(struct
> selinux_state *state)
> > }
> >
> > measure_rc = ima_measure_critical_data("selinux", "selinux-policy-
> hash",
> > - policy, policy_len, true);
> > + policy, policy_len, true,
> > + NULL, 0);
> >
> > vfree(policy);
> > }
> >