Re: [PATCH v2 2/3] ima: Return int in the functions to measure a buffer

Lakshmi Ramasubramanian
2021-07-01T16:13:53Z

On 7/1/2021 5:55 AM, Roberto Sassu wrote:
> ima_measure_critical_data() and process_buffer_measurement() currently
> don't return a result. A caller wouldn't be able to know whether those
> functions were executed successfully.
>
> This patch modifies the return type from void to int, and returns 0 if the
> buffer has been successfully measured, a negative value otherwise.
>
> Also, this patch does not modify the behavior of existing callers by
> processing the returned value. Instead, the value is stored in a variable
> marked as __maybe_unused.
>
> Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
> ---
> include/linux/ima.h | 15 +++---
> security/integrity/ima/ima.h | 10 ++--
> security/integrity/ima/ima_appraise.c | 4 +-
> security/integrity/ima/ima_asymmetric_keys.c | 4 +-
> security/integrity/ima/ima_init.c | 6 ++-
> security/integrity/ima/ima_main.c | 48 ++++++++++++--------
> security/integrity/ima/ima_queue_keys.c | 15 +++---
> security/selinux/ima.c | 10 ++--
> 8 files changed, 66 insertions(+), 46 deletions(-)
>
> diff --git a/include/linux/ima.h b/include/linux/ima.h
> index 81e830d01ced..60492263aa64 100644
> --- a/include/linux/ima.h
> +++ b/include/linux/ima.h
> @@ -35,10 +35,10 @@ extern void ima_post_path_mknod(struct user_namespace *mnt_userns,
> extern int ima_file_hash(struct file *file, char *buf, size_t buf_size);
> extern int ima_inode_hash(struct inode *inode, char *buf, size_t buf_size);
> extern void ima_kexec_cmdline(int kernel_fd, const void *buf, int size);
> -extern void ima_measure_critical_data(const char *event_label,
> - const char *event_name,
> - const void *buf, size_t buf_len,
> - bool hash);
> +extern int ima_measure_critical_data(const char *event_label,
> + const char *event_name,
> + const void *buf, size_t buf_len,
> + bool hash);
>
> #ifdef CONFIG_IMA_APPRAISE_BOOTPARAM
> extern void ima_appraise_parse_cmdline(void);
> @@ -144,10 +144,13 @@ static inline int ima_inode_hash(struct inode *inode, char *buf, size_t buf_size
>
> static inline void ima_kexec_cmdline(int kernel_fd, const void *buf, int size) {}
>
> -static inline void ima_measure_critical_data(const char *event_label,
> +static inline int ima_measure_critical_data(const char *event_label,
> const char *event_name,
> const void *buf, size_t buf_len,
> - bool hash) {}
> + bool hash)
> +{
> + return -ENOENT;
> +}
>
> #endif /* CONFIG_IMA */
>
> diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
> index f0e448ed1f9f..03db221324c3 100644
> --- a/security/integrity/ima/ima.h
> +++ b/security/integrity/ima/ima.h
> @@ -264,11 +264,11 @@ void ima_store_measurement(struct integrity_iint_cache *iint, struct file *file,
> struct evm_ima_xattr_data *xattr_value,
> int xattr_len, const struct modsig *modsig, int pcr,
> struct ima_template_desc *template_desc);
> -void 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);
> +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);
> void ima_audit_measurement(struct integrity_iint_cache *iint,
> const unsigned char *filename);
> int ima_alloc_init_template(struct ima_event_data *event_data,
> diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
> index ef9dcfce45d4..275a2377743f 100644
> --- a/security/integrity/ima/ima_appraise.c
> +++ b/security/integrity/ima/ima_appraise.c
> @@ -345,6 +345,7 @@ int ima_check_blacklist(struct integrity_iint_cache *iint,
> enum hash_algo hash_algo;
> const u8 *digest = NULL;
> u32 digestsize = 0;
> + int process_rc __maybe_unused;
> int rc = 0;
>
> if (!(iint->flags & IMA_CHECK_BLACKLIST))
> @@ -355,7 +356,8 @@ int ima_check_blacklist(struct integrity_iint_cache *iint,
>
> rc = is_binary_blacklisted(digest, digestsize);
> if ((rc == -EPERM) && (iint->flags & IMA_MEASURE))
> - process_buffer_measurement(&init_user_ns, NULL, digest, digestsize,
> + process_rc = process_buffer_measurement(&init_user_ns,
I think there is no need to make this change now. If and when
ima_check_blacklist() needs to look at the return value of p_b_m(), this
change can be made.

> + NULL, digest, digestsize,
> "blacklisted-hash", NONE,
> pcr, NULL, false);
> }
> diff --git a/security/integrity/ima/ima_asymmetric_keys.c b/security/integrity/ima/ima_asymmetric_keys.c
> index c985418698a4..910367cdd920 100644
> --- a/security/integrity/ima/ima_asymmetric_keys.c
> +++ b/security/integrity/ima/ima_asymmetric_keys.c
> @@ -31,6 +31,7 @@ void ima_post_key_create_or_update(struct key *keyring, struct key *key,
> unsigned long flags, bool create)
> {
> bool queued = false;
> + int ret __maybe_unused;
>
> /* Only asymmetric keys are handled by this hook. */
> if (key->type != &key_type_asymmetric)
> @@ -60,7 +61,8 @@ void ima_post_key_create_or_update(struct key *keyring, struct key *key,
> * if the IMA policy is configured to measure a key linked
> * to the given keyring.
> */
> - process_buffer_measurement(&init_user_ns, NULL, payload, payload_len,
> + ret = process_buffer_measurement(&init_user_ns, NULL,
> + payload, payload_len,
Same comment as in ima_check_blacklist() - this change be made when needed.

> keyring->description, KEY_CHECK, 0,
> keyring->description, false);
> }
> diff --git a/security/integrity/ima/ima_init.c b/security/integrity/ima/ima_init.c
> index 5076a7d9d23e..6790eea88db8 100644
> --- a/security/integrity/ima/ima_init.c
> +++ b/security/integrity/ima/ima_init.c
> @@ -118,6 +118,7 @@ void __init ima_load_x509(void)
>
> int __init ima_init(void)
> {
> + int measure_rc __maybe_unused;
> int rc;
>
> ima_tpm_chip = tpm_default_chip();
> @@ -153,8 +154,9 @@ int __init ima_init(void)
>
> ima_init_key_queue();
>
> - ima_measure_critical_data("kernel_info", "kernel_version",
> - UTS_RELEASE, strlen(UTS_RELEASE), false);
> + measure_rc = ima_measure_critical_data("kernel_info", "kernel_version",
> + UTS_RELEASE, strlen(UTS_RELEASE),
> + false);
Same comment as in ima_check_blacklist() - this change be made when needed.

>
> return rc;
> }
> diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
> index 8ef1fa357e0c..3386e7436440 100644
> --- a/security/integrity/ima/ima_main.c
> +++ b/security/integrity/ima/ima_main.c
> @@ -827,7 +827,7 @@ int ima_post_load_data(char *buf, loff_t size,
> return 0;
> }
>
> -/*
> +/**
> * process_buffer_measurement - Measure the buffer or the buffer data hash
> * @mnt_userns: user namespace of the mount the inode was found from
> * @inode: inode associated with the object being measured (NULL for KEY_CHECK)
> @@ -840,12 +840,15 @@ int ima_post_load_data(char *buf, loff_t size,
> * @buf_hash: measure buffer data hash
> *
> * 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.
> */
> -void 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)
> +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)
> {
> int ret = 0;
> const char *audit_cause = "ENOMEM";
> @@ -867,7 +870,7 @@ void process_buffer_measurement(struct user_namespace *mnt_userns,
> u32 secid;
>
> if (!ima_policy_flag)
> - return;
> + return -ENOENT;
>
> template = ima_template_desc_buf();
> if (!template) {
> @@ -889,7 +892,7 @@ void process_buffer_measurement(struct user_namespace *mnt_userns,
> secid, 0, func, &pcr, &template,
> func_data);
> if (!(action & IMA_MEASURE))
> - return;
> + return -ENOENT;
> }
>
> if (!pcr)
> @@ -937,7 +940,7 @@ void process_buffer_measurement(struct user_namespace *mnt_userns,
> func_measure_str(func),
> audit_cause, ret, 0, ret);
>
> - return;
> + return ret;
> }
>
> /**
> @@ -951,6 +954,7 @@ void process_buffer_measurement(struct user_namespace *mnt_userns,
> void ima_kexec_cmdline(int kernel_fd, const void *buf, int size)
> {
> struct fd f;
> + int ret __maybe_unused;
>
> if (!buf || !size)
> return;
> @@ -959,9 +963,10 @@ void ima_kexec_cmdline(int kernel_fd, const void *buf, int size)
> if (!f.file)
> return;
>
> - process_buffer_measurement(file_mnt_user_ns(f.file), file_inode(f.file),
> - buf, size, "kexec-cmdline", KEXEC_CMDLINE, 0,
> - NULL, false);
> + ret = process_buffer_measurement(file_mnt_user_ns(f.file),
> + file_inode(f.file), buf, size,
> + "kexec-cmdline", KEXEC_CMDLINE, 0,
> + NULL, false);
Since the return value of p_b_m() is not used here, this change can be
made when needed.

> fdput(f);
> }
>
> @@ -977,18 +982,21 @@ void ima_kexec_cmdline(int kernel_fd, const void *buf, int size)
> * 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.
> */
> -void ima_measure_critical_data(const char *event_label,
> - const char *event_name,
> - const void *buf, size_t buf_len,
> - bool hash)
> +int ima_measure_critical_data(const char *event_label,
> + const char *event_name,
> + const void *buf, size_t buf_len,
> + bool hash)
> {
> if (!event_name || !event_label || !buf || !buf_len)
> - return;
> + return -ENOPARAM;
>
> - process_buffer_measurement(&init_user_ns, NULL, buf, buf_len, event_name,
> - CRITICAL_DATA, 0, event_label,
> - hash);
> + return process_buffer_measurement(&init_user_ns, NULL, buf, buf_len,
> + event_name, CRITICAL_DATA, 0,
> + event_label, hash);
> }
>
> 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 979ef6c71f3d..e3047ce64f39 100644
> --- a/security/integrity/ima/ima_queue_keys.c
> +++ b/security/integrity/ima/ima_queue_keys.c
> @@ -134,6 +134,7 @@ void ima_process_queued_keys(void)
> {
> struct ima_key_entry *entry, *tmp;
> bool process = false;
> + int ret __maybe_unused;
>
> if (ima_process_keys)
> return;
> @@ -159,13 +160,13 @@ void ima_process_queued_keys(void)
>
> list_for_each_entry_safe(entry, tmp, &ima_keys, list) {
> if (!timer_expired)
> - process_buffer_measurement(&init_user_ns, NULL,
> - entry->payload,
> - entry->payload_len,
> - entry->keyring_name,
> - KEY_CHECK, 0,
> - entry->keyring_name,
> - false);
> + ret = process_buffer_measurement(&init_user_ns, NULL,
> + entry->payload,
> + entry->payload_len,
> + entry->keyring_name,
> + KEY_CHECK, 0,
> + entry->keyring_name,
> + false);
Same comment as above.

> list_del(&entry->list);
> ima_free_key_entry(entry);
> }
> diff --git a/security/selinux/ima.c b/security/selinux/ima.c
> index 34d421861bfc..4db9fa211638 100644
> --- a/security/selinux/ima.c
> +++ b/security/selinux/ima.c
> @@ -75,6 +75,7 @@ void selinux_ima_measure_state_locked(struct selinux_state *state)
> char *state_str = NULL;
> void *policy = NULL;
> size_t policy_len;
> + int measure_rc __maybe_unused;
> int rc = 0;
>
> WARN_ON(!mutex_is_locked(&state->policy_mutex));
> @@ -85,8 +86,9 @@ void selinux_ima_measure_state_locked(struct selinux_state *state)
> return;
> }
>
> - ima_measure_critical_data("selinux", "selinux-state",
> - state_str, strlen(state_str), false);
> + measure_rc = ima_measure_critical_data("selinux", "selinux-state",
> + state_str, strlen(state_str),
> + false);
Since the return value of ima_measure_critical_data() is not used here,
this change can be made when needed.

>
> kfree(state_str);
>
> @@ -102,8 +104,8 @@ void selinux_ima_measure_state_locked(struct selinux_state *state)
> return;
> }
>
> - ima_measure_critical_data("selinux", "selinux-policy-hash",
> - policy, policy_len, true);
> + measure_rc = ima_measure_critical_data("selinux", "selinux-policy-hash",
> + policy, policy_len, true);
Same comment as above.

-lakshmi

>
> vfree(policy);
> }
>