[PATCH v2 11/11] ima: Support additional conditionals in the KEXEC_CMDLINE hook function
Tyler Hicks
tyhicks at linux.microsoft.com
Wed Jul 1 14:38:52 UTC 2020
On 2020-07-01 16:04:16, Dave Young wrote:
> 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 at linux.microsoft.com>
> > Cc: Eric Biederman <ebiederm at xmission.com>
> > Cc: kexec at lists.infradead.org
> > ---
> >
> > * 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 at lists.infradead.org
> > 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.
Ah, very good question. This IMA hook (KEXEC_CMDLINE) only measures the
string passed to the cmdline argument of the kexec_file_load(2) syscall.
However, kernel commandline options injected into a kernel with the
CONFIG_CMDLINE or CONFIG_CMDLINE_EXTEND Kconfig options would still be
measured, as part of the vmlinux as a whole, by the KEXEC_KERNEL_CHECK
IMA hook.
Tyler
>
> Thanks
> Dave
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