Messages in this thread | | | Subject | Re: [PATCH v3 4/5] LSM: Define SELinux function to measure security state | From | Lakshmi Ramasubramanian <> | Date | Mon, 20 Jul 2020 08:17:28 -0700 |
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On 7/20/20 7:31 AM, Stephen Smalley wrote:
>> +void __init selinux_init_measurement(void) >> +{ >> + int i; >> + >> + /* >> + * enabled >> + * enforcing >> + * checkreqport > > checkreqprot (spelling) :( - will fix that.
> > What about initialized? Or do you consider that to be implicitly > true/1 else we wouldn't be taking a measurement? Only caveat there is > that it provides one more means of disabling measurements (at the same > time as disabling enforcement) by setting it to false/0 via kernel > write flaw. Yes - I was thinking measuring SELinux state would be meaningful only when initialized is set to true/1.
I can include "initialized" as well in the measurement.
> >> + * All policy capability flags >> + */ >> + selinux_state_count = 3 + __POLICYDB_CAPABILITY_MAX; >> + >> + selinux_state_string_len = snprintf(NULL, 0, str_format, >> + "enabled", 0); >> + selinux_state_string_len += snprintf(NULL, 0, str_format, >> + "enforcing", 0); >> + selinux_state_string_len += snprintf(NULL, 0, str_format, >> + "checkreqprot", 0); >> + for (i = 3; i < selinux_state_count; i++) { >> + selinux_state_string_len += >> + snprintf(NULL, 0, str_format, >> + selinux_policycap_names[i-3], 0); >> + } > > What's the benefit of this pattern versus just making the loop go from > 0 to __POLICYDB_CAPABILITY_MAX and using selinux_policycap_names[i]?
No real benefit - I was just trying to use selinux_state_count. I'll change the loop to go from 0 to POLICY_CAP_MAX
> >> +void selinux_measure_state(struct selinux_state *selinux_state) >> +{ >> + void *policy = NULL; >> + void *policy_hash = NULL; >> + size_t curr, buflen; >> + int i, policy_hash_len, rc = 0; >> + >> + if (!selinux_initialized(selinux_state)) { >> + pr_warn("%s: SELinux not yet initialized.\n", __func__); >> + return; >> + } > > We could measure the global state variables before full SELinux > initialization (i.e. policy load). > Only the policy hash depends on having loaded the policy.
Thanks for the information. I'll measure the state variables always and measure policy only if "initialized" is true/1.
> >> + >> + if (!selinux_state_string) { >> + pr_warn("%s: Buffer for state not allocated.\n", __func__); >> + return; >> + } >> + >> + curr = snprintf(selinux_state_string, selinux_state_string_len, >> + str_format, "enabled", >> + !selinux_disabled(selinux_state)); >> + curr += snprintf((selinux_state_string + curr), >> + (selinux_state_string_len - curr), >> + str_format, "enforcing", >> + enforcing_enabled(selinux_state)); >> + curr += snprintf((selinux_state_string + curr), >> + (selinux_state_string_len - curr), >> + str_format, "checkreqprot", >> + selinux_checkreqprot(selinux_state)); >> + >> + for (i = 3; i < selinux_state_count; i++) { >> + curr += snprintf((selinux_state_string + curr), >> + (selinux_state_string_len - curr), >> + str_format, >> + selinux_policycap_names[i - 3], >> + selinux_state->policycap[i - 3]); >> + } > > Same question here as for the previous loop; seems cleaner to go from > 0 to __POLICYDB_CAPABILITY_MAX and use [i]. Will change it.
> > What public git tree / branch would you recommend trying to use your > patches against? Didn't seem to apply to any of the obvious ones. >
Please try it on Mimi's next-integrity branch
https://git.kernel.org/pub/scm/linux/kernel/git/zohar/linux-integrity.git/log/?h=next-integrity
You can try it on Linus's mainline as well if you apply the following patch first (have mentioned that in the Cover letter as well)
https://patchwork.kernel.org/patch/11612989/
Thanks for trying out the changes. Please let me know the defects you find.
Just to let you know - I am making the following change (will update in the next patch):
=> Save the last policy hash and state string in selinux_state struct. => Measure policy and hash only if it has changed since the last measurement. => Also, suffix the IMA event name used with time stamp. For example,
10 e32e...5ac3 ima-buf sha256:86e8...4594 selinux-state-1595257807:874963248 656e61626c65643d313b656e666f7263696e673d303b636865636b72657170726f743d313b6e6574706565723d313b6f70656e7065726d3d313b657874736f636b636c6173733d313b616c776179736e6574776f726b3d303b6367726f75707365636c6162656c3d313b6e6e706e6f737569647472616e736974696f6e3d313b67656e66737365636c6162656c73796d6c696e6b3d303b
10 f4a7...9408 ima-buf sha256:4941...68fc selinux-policy-hash-1595257807:874963248 8d1d...1834
The above will ensure the following sequence will be measured: #1 State A - Measured #2 Change from State A to State B - Measured #3 Change from State B back to State A - Since the measured data is same as in #1, the change will be measured only if the event name is different between #1 and #3
thanks, -lakshmi
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