Re: [PATCH v2 11/11] ima: Support additional conditionals in the KEXEC_CMDLINE hook function
From: Dave Young
Date: Wed Jul 01 2020 - 04:05:38 EST
Hi,
On 06/26/20 at 05:39pm, Tyler Hicks wrote:
> Take the properties of the kexec kernel's inode and the current task
> ownership into consideration when matching a KEXEC_CMDLINE operation to
> the rules in the IMA policy. This allows for some uniformity when
> writing IMA policy rules for KEXEC_KERNEL_CHECK, KEXEC_INITRAMFS_CHECK,
> and KEXEC_CMDLINE operations.
>
> Prior to this patch, it was not possible to write a set of rules like
> this:
>
> dont_measure func=KEXEC_KERNEL_CHECK obj_type=foo_t
> dont_measure func=KEXEC_INITRAMFS_CHECK obj_type=foo_t
> dont_measure func=KEXEC_CMDLINE obj_type=foo_t
> measure func=KEXEC_KERNEL_CHECK
> measure func=KEXEC_INITRAMFS_CHECK
> measure func=KEXEC_CMDLINE
>
> The inode information associated with the kernel being loaded by a
> kexec_kernel_load(2) syscall can now be included in the decision to
> measure or not
>
> Additonally, the uid, euid, and subj_* conditionals can also now be
> used in KEXEC_CMDLINE rules. There was no technical reason as to why
> those conditionals weren't being considered previously other than
> ima_match_rules() didn't have a valid inode to use so it immediately
> bailed out for KEXEC_CMDLINE operations rather than going through the
> full list of conditional comparisons.
>
> Signed-off-by: Tyler Hicks <tyhicks@xxxxxxxxxxxxxxxxxxx>
> Cc: Eric Biederman <ebiederm@xxxxxxxxxxxx>
> Cc: kexec@xxxxxxxxxxxxxxxxxxx
> ---
>
> * v2
> - Moved the inode parameter of process_buffer_measurement() to be the
> first parameter so that it more closely matches process_masurement()
>
> include/linux/ima.h | 4 ++--
> kernel/kexec_file.c | 2 +-
> security/integrity/ima/ima.h | 2 +-
> security/integrity/ima/ima_api.c | 2 +-
> security/integrity/ima/ima_appraise.c | 2 +-
> security/integrity/ima/ima_asymmetric_keys.c | 2 +-
> security/integrity/ima/ima_main.c | 23 +++++++++++++++-----
> security/integrity/ima/ima_policy.c | 17 +++++----------
> security/integrity/ima/ima_queue_keys.c | 2 +-
> 9 files changed, 31 insertions(+), 25 deletions(-)
>
> diff --git a/include/linux/ima.h b/include/linux/ima.h
> index 9164e1534ec9..d15100de6cdd 100644
> --- a/include/linux/ima.h
> +++ b/include/linux/ima.h
> @@ -25,7 +25,7 @@ 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 int ima_file_hash(struct file *file, char *buf, size_t buf_size);
> -extern void ima_kexec_cmdline(const void *buf, int size);
> +extern void ima_kexec_cmdline(int kernel_fd, const void *buf, int size);
>
> #ifdef CONFIG_IMA_KEXEC
> extern void ima_add_kexec_buffer(struct kimage *image);
> @@ -103,7 +103,7 @@ static inline int ima_file_hash(struct file *file, char *buf, size_t buf_size)
> return -EOPNOTSUPP;
> }
>
> -static inline void ima_kexec_cmdline(const void *buf, int size) {}
> +static inline void ima_kexec_cmdline(int kernel_fd, const void *buf, int size) {}
> #endif /* CONFIG_IMA */
>
> #ifndef CONFIG_IMA_KEXEC
> diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
> index bb05fd52de85..07df431c1f21 100644
> --- a/kernel/kexec_file.c
> +++ b/kernel/kexec_file.c
> @@ -287,7 +287,7 @@ kimage_file_prepare_segments(struct kimage *image, int kernel_fd, int initrd_fd,
> goto out;
> }
>
> - ima_kexec_cmdline(image->cmdline_buf,
> + ima_kexec_cmdline(kernel_fd, image->cmdline_buf,
> image->cmdline_buf_len - 1);
> }
>
> diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
> index 59ec28f5c117..ff2bf57ff0c7 100644
> --- a/security/integrity/ima/ima.h
> +++ b/security/integrity/ima/ima.h
> @@ -265,7 +265,7 @@ 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(const void *buf, int size,
> +void process_buffer_measurement(struct inode *inode, const void *buf, int size,
> const char *eventname, enum ima_hooks func,
> int pcr, const char *keyring);
> void ima_audit_measurement(struct integrity_iint_cache *iint,
> diff --git a/security/integrity/ima/ima_api.c b/security/integrity/ima/ima_api.c
> index bf22de8b7ce0..4f39fb93f278 100644
> --- a/security/integrity/ima/ima_api.c
> +++ b/security/integrity/ima/ima_api.c
> @@ -162,7 +162,7 @@ void ima_add_violation(struct file *file, const unsigned char *filename,
>
> /**
> * ima_get_action - appraise & measure decision based on policy.
> - * @inode: pointer to inode to measure
> + * @inode: pointer to the inode associated with the object being validated
> * @cred: pointer to credentials structure to validate
> * @secid: secid of the task being validated
> * @mask: contains the permission mask (MAY_READ, MAY_WRITE, MAY_EXEC,
> diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
> index a9649b04b9f1..6c52bf7ea7f0 100644
> --- a/security/integrity/ima/ima_appraise.c
> +++ b/security/integrity/ima/ima_appraise.c
> @@ -328,7 +328,7 @@ 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(digest, digestsize,
> + process_buffer_measurement(NULL, digest, digestsize,
> "blacklisted-hash", NONE,
> pcr, NULL);
> }
> diff --git a/security/integrity/ima/ima_asymmetric_keys.c b/security/integrity/ima/ima_asymmetric_keys.c
> index aaae80c4e376..1c68c500c26f 100644
> --- a/security/integrity/ima/ima_asymmetric_keys.c
> +++ b/security/integrity/ima/ima_asymmetric_keys.c
> @@ -58,7 +58,7 @@ 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(payload, payload_len,
> + process_buffer_measurement(NULL, payload, payload_len,
> keyring->description, KEY_CHECK, 0,
> keyring->description);
> }
> diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
> index 8351b2fd48e0..8a91711ca79b 100644
> --- a/security/integrity/ima/ima_main.c
> +++ b/security/integrity/ima/ima_main.c
> @@ -726,6 +726,7 @@ int ima_load_data(enum kernel_load_data_id id)
>
> /*
> * process_buffer_measurement - Measure the buffer to ima log.
> + * @inode: inode associated with the object being measured (NULL for KEY_CHECK)
> * @buf: pointer to the buffer that needs to be added to the log.
> * @size: size of buffer(in bytes).
> * @eventname: event name to be used for the buffer entry.
> @@ -735,7 +736,7 @@ int ima_load_data(enum kernel_load_data_id id)
> *
> * Based on policy, the buffer is measured into the ima log.
> */
> -void process_buffer_measurement(const void *buf, int size,
> +void process_buffer_measurement(struct inode *inode, const void *buf, int size,
> const char *eventname, enum ima_hooks func,
> int pcr, const char *keyring)
> {
> @@ -768,7 +769,7 @@ void process_buffer_measurement(const void *buf, int size,
> */
> if (func) {
> security_task_getsecid(current, &secid);
> - action = ima_get_action(NULL, current_cred(), secid, 0, func,
> + action = ima_get_action(inode, current_cred(), secid, 0, func,
> &pcr, &template, keyring);
> if (!(action & IMA_MEASURE))
> return;
> @@ -823,16 +824,26 @@ void process_buffer_measurement(const void *buf, int size,
>
> /**
> * ima_kexec_cmdline - measure kexec cmdline boot args
> + * @kernel_fd: file descriptor of the kexec kernel being loaded
> * @buf: pointer to buffer
> * @size: size of buffer
> *
> * Buffers can only be measured, not appraised.
> */
> -void ima_kexec_cmdline(const void *buf, int size)
> +void ima_kexec_cmdline(int kernel_fd, const void *buf, int size)
> {
> - if (buf && size != 0)
> - process_buffer_measurement(buf, size, "kexec-cmdline",
> - KEXEC_CMDLINE, 0, NULL);
> + struct fd f;
> +
> + if (!buf || !size)
> + return;
> +
> + f = fdget(kernel_fd);
> + if (!f.file)
> + return;
> +
> + process_buffer_measurement(file_inode(f.file), buf, size,
> + "kexec-cmdline", KEXEC_CMDLINE, 0, NULL);
> + fdput(f);
> }
>
> static int __init init_ima(void)
> diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
> index 5eb14b567a31..294323b36d06 100644
> --- a/security/integrity/ima/ima_policy.c
> +++ b/security/integrity/ima/ima_policy.c
> @@ -443,13 +443,9 @@ static bool ima_match_rules(struct ima_rule_entry *rule, struct inode *inode,
> {
> int i;
>
> - if ((func == KEXEC_CMDLINE) || (func == KEY_CHECK)) {
> - if ((rule->flags & IMA_FUNC) && (rule->func == func)) {
> - if (func == KEY_CHECK)
> - return ima_match_keyring(rule, keyring, cred);
> - return true;
> - }
> - return false;
> + if (func == KEY_CHECK) {
> + return (rule->flags & IMA_FUNC) && (rule->func == func) &&
> + ima_match_keyring(rule, keyring, cred);
> }
> if ((rule->flags & IMA_FUNC) &&
> (rule->func != func && func != POST_SETATTR))
> @@ -1007,10 +1003,9 @@ static bool ima_validate_rule(struct ima_rule_entry *entry)
> if (entry->action & ~(MEASURE | DONT_MEASURE))
> return false;
>
> - if (entry->flags & ~(IMA_FUNC | IMA_PCR))
> - return false;
> -
> - if (ima_rule_contains_lsm_cond(entry))
> + if (entry->flags & ~(IMA_FUNC | IMA_FSMAGIC | IMA_UID |
> + IMA_FOWNER | IMA_FSUUID |
> + IMA_EUID | IMA_PCR | IMA_FSNAME))
> return false;
>
> break;
> diff --git a/security/integrity/ima/ima_queue_keys.c b/security/integrity/ima/ima_queue_keys.c
> index 56ce24a18b66..69a8626a35c0 100644
> --- a/security/integrity/ima/ima_queue_keys.c
> +++ b/security/integrity/ima/ima_queue_keys.c
> @@ -158,7 +158,7 @@ void ima_process_queued_keys(void)
>
> list_for_each_entry_safe(entry, tmp, &ima_keys, list) {
> if (!timer_expired)
> - process_buffer_measurement(entry->payload,
> + process_buffer_measurement(NULL, entry->payload,
> entry->payload_len,
> entry->keyring_name,
> KEY_CHECK, 0,
> --
> 2.25.1
>
>
> _______________________________________________
> kexec mailing list
> kexec@xxxxxxxxxxxxxxxxxxx
> http://lists.infradead.org/mailman/listinfo/kexec
>
Although I still do not understand the deep knowledge of IMA, I
still wonder to know what is the effect to the behavior changes end user
visible. Does it work with a kernel built-in commandline? eg no
cmdlien passed at all.
Thanks
Dave