Re: [PATCH v3 1/4] added a new ima policy func buffer_check, and ima hook to measure the buffer hash into ima

Mimi Zohar
2019-05-02T16:52:23Z

On Mon, 2019-04-29 at 14:47 -0700, Prakhar Srivastava wrote:
> From: Prakhar Srivastava <prsriva02@gmail.com>
>
> added a new ima policy func buffer_check, and ima hook to
> measure the buffer hash into ima logs.

When defining a new LSN/IMA hook please conform to the existing naming
conventions.  Generally LSM hooks are specific to a particular
function.  In this instance, the name of the hook would be something
like security_kexec_cmdline() or ima_kexec_cmdline(), which would call
the generic process_buffer_measurement() you've defined.

Mimi

>
> Signed-off-by: Prakhar Srivastava <prsriva02@gmail.com>
> ---
> Documentation/ABI/testing/ima_policy | 1 +
> include/linux/ima.h | 5 ++
> security/integrity/ima/ima.h | 1 +
> security/integrity/ima/ima_api.c | 1 +
> security/integrity/ima/ima_main.c | 89 ++++++++++++++++++++++++++++
> security/integrity/ima/ima_policy.c | 8 +++
> 6 files changed, 105 insertions(+)
>
> diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy
> index 74c6702de74e..12cfe3ff2dea 100644
> --- a/Documentation/ABI/testing/ima_policy
> +++ b/Documentation/ABI/testing/ima_policy
> @@ -29,6 +29,7 @@ Description:
> base: func:= [BPRM_CHECK][MMAP_CHECK][CREDS_CHECK][FILE_CHECK][MODULE_CHECK]
> [FIRMWARE_CHECK]
> [KEXEC_KERNEL_CHECK] [KEXEC_INITRAMFS_CHECK]
> + [BUFFER_CHECK]
> mask:= [[^]MAY_READ] [[^]MAY_WRITE] [[^]MAY_APPEND]
> [[^]MAY_EXEC]
> fsmagic:= hex value
> diff --git a/include/linux/ima.h b/include/linux/ima.h
> index dc12fbcf484c..f0abade74707 100644
> --- a/include/linux/ima.h
> +++ b/include/linux/ima.h
> @@ -26,6 +26,8 @@ extern int ima_read_file(struct file *file, enum kernel_read_file_id id);
> extern int ima_post_read_file(struct file *file, void *buf, loff_t size,
> enum kernel_read_file_id id);
> extern void ima_post_path_mknod(struct dentry *dentry);
> +extern void ima_buffer_check(const void *buff, int size,
> + const char *eventname);
>
> #ifdef CONFIG_IMA_KEXEC
> extern void ima_add_kexec_buffer(struct kimage *image);
> @@ -92,6 +94,9 @@ static inline void ima_post_path_mknod(struct dentry *dentry)
> return;
> }
>
> +static inline void ima_buffer_check(const void *buff, int size,
> + const char *eventname)
> +{}
> #endif /* CONFIG_IMA */
>
> #ifndef CONFIG_IMA_KEXEC
> diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
> index d213e835c498..de70df132575 100644
> --- a/security/integrity/ima/ima.h
> +++ b/security/integrity/ima/ima.h
> @@ -184,6 +184,7 @@ static inline unsigned long ima_hash_key(u8 *digest)
> hook(KEXEC_KERNEL_CHECK) \
> hook(KEXEC_INITRAMFS_CHECK) \
> hook(POLICY_CHECK) \
> + hook(BUFFER_CHECK) \
> hook(MAX_CHECK)
> #define __ima_hook_enumify(ENUM) ENUM,
>
> diff --git a/security/integrity/ima/ima_api.c b/security/integrity/ima/ima_api.c
> index c7505fb122d4..cb3f67b366f1 100644
> --- a/security/integrity/ima/ima_api.c
> +++ b/security/integrity/ima/ima_api.c
> @@ -169,6 +169,7 @@ void ima_add_violation(struct file *file, const unsigned char *filename,
> * subj=, obj=, type=, func=, mask=, fsmagic=
> * subj,obj, and type: are LSM specific.
> * func: FILE_CHECK | BPRM_CHECK | CREDS_CHECK | MMAP_CHECK | MODULE_CHECK
> + * | BUFFER_CHECK
> * mask: contains the permission mask
> * fsmagic: hex value
> *
> diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
> index 357edd140c09..3db3f3966ac7 100644
> --- a/security/integrity/ima/ima_main.c
> +++ b/security/integrity/ima/ima_main.c
> @@ -576,6 +576,95 @@ int ima_load_data(enum kernel_load_data_id id)
> return 0;
> }
>
> +/*
> + * process_buffer_measurement - Measure the buffer passed to ima log.
> + * (Instead of using the file hash the buffer hash is used).
> + * @buff - The buffer that needs to be added to the log
> + * @size - size of buffer(in bytes)
> + * @eventname - this is eventname used for the various buffers
> + * that can be measured.
> + *
> + * The buffer passed is added to the ima logs.
> + * If the sig template is used, then the sig field contains the buffer.
> + *
> + * On success return 0.
> + * On error cases surface errors from ima calls.
> + */
> +static int process_buffer_measurement(const void *buff, int size,
> + const char *eventname, const struct cred *cred,
> + u32 secid)
> +{
> + int ret = -EINVAL;
> + struct ima_template_entry *entry = NULL;
> + struct integrity_iint_cache tmp_iint, *iint = &tmp_iint;
> + struct ima_event_data event_data = {iint, NULL, NULL,
> + NULL, 0, NULL};
> + struct {
> + struct ima_digest_data hdr;
> + char digest[IMA_MAX_DIGEST_SIZE];
> + } hash;
> + int violation = 0;
> + int pcr = CONFIG_IMA_MEASURE_PCR_IDX;
> +
> + if (!buff || size == 0 || !eventname)
> + goto err_out;
> +
> + if (ima_get_action(NULL, cred, secid, 0, BUFFER_CHECK, &pcr)
> + != IMA_MEASURE)
> + goto err_out;
> +
> + memset(iint, 0, sizeof(*iint));
> + memset(&hash, 0, sizeof(hash));
> +
> + event_data.filename = eventname;
> +
> + iint->ima_hash = &hash.hdr;
> + iint->ima_hash->algo = ima_hash_algo;
> + iint->ima_hash->length = hash_digest_size[ima_hash_algo];
> +
> + ret = ima_calc_buffer_hash(buff, size, iint->ima_hash);
> + if (ret < 0)
> + goto err_out;
> +
> + ret = ima_alloc_init_template(&event_data, &entry);
> + if (ret < 0)
> + goto err_out;
> +
> + ret = ima_store_template(entry, violation, NULL,
> + buff, pcr);
> + if (ret < 0) {
> + ima_free_template_entry(entry);
> + goto err_out;
> + }
> +
> + return 0;
> +
> +err_out:
> + pr_err("Error in adding buffer measure: %d\n", ret);
> + return ret;
> +}
> +
> +/**
> + * ima_buffer_check - based on policy, collect & store buffer measurement
> + * @buf: pointer to buffer
> + * @size: size of buffer
> + * @eventname: event name identifier
> + *
> + * Buffers can only be measured, not appraised. The buffer identifier
> + * is used as the measurement list entry name (eg. boot_cmdline).
> + */
> +void ima_buffer_check(const void *buf, int size, const char *eventname)
> +{
> + u32 secid;
> +
> + if (buf && size != 0 && eventname) {
> + security_task_getsecid(current, &secid);
> + process_buffer_measurement(buf, size, eventname,
> + current_cred(), secid);
> + }
> +}
> +
> +
> static int __init init_ima(void)
> {
> int error;
> diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
> index e0cc323f948f..b12551ed191c 100644
> --- a/security/integrity/ima/ima_policy.c
> +++ b/security/integrity/ima/ima_policy.c
> @@ -291,6 +291,12 @@ static bool ima_match_rules(struct ima_rule_entry *rule, struct inode *inode,
> {
> int i;
>
> + // Incase of BUFFER_CHECK, Inode is NULL
> + if (!inode) {
> + if ((rule->flags & IMA_FUNC) && (rule->func == func))
> + return true;
> + return false;
> + }
> if ((rule->flags & IMA_FUNC) &&
> (rule->func != func && func != POST_SETATTR))
> return false;
> @@ -869,6 +875,8 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
> entry->func = KEXEC_INITRAMFS_CHECK;
> else if (strcmp(args[0].from, "POLICY_CHECK") == 0)
> entry->func = POLICY_CHECK;
> + else if (strcmp(args[0].from, "BUFFER_CHECK") == 0)
> + entry->func = BUFFER_CHECK;
> else
> result = -EINVAL;
> if (!result)