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fix: inaccuracy in SELinux policy evaluation example #112

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fix: inaccuracy in SELinux policy evaluation example #112

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4 changes: 2 additions & 2 deletions secure-computer-systems/09-selinux.md
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Expand Up @@ -205,12 +205,12 @@ Again, DAC is fine.

**Commands for process #1**:

1. No access. `staff_t` does have read access to `home_t`. The effective sensitivity level of s0 is lower than s5, we fail MLS check. No access.
1. No access. `staff_t` has read access to `user_home_t` so it passes type enforcement (DTE), but the effective sensitivity level of s0 is lower than s5, so we fail MLS check. No access.
2. No access. Effective level is still s0 < s5.
3. No access. staff_t can execute the file of type `aide_exec_t` but staff_t has no transition to type aide_t, it will remain at the same type and have no permissions. If staff_t could transition to type aide_t then it would get the mlsfilereadtoclr and mlsfilewritetoclr attributes, allowing us to use the clearance level s15 instead of the effective level s0, this would allow access.

**Commands for process #2**:

1. Allowed. Our **clearance** level is s15, which allows us to read something with sensitivity level s5. Notice that sysadm_t has both `mlsfilewritetoclr` and `mlsfilereadtoclr`. This means when reading and writing we can use the clearance level instead of the effective level.
2. Allowed. Again, clearance of s15 > s5.
3. Allowed. sysadm_t can execute the file of type `aide_exec_t` and transition to type `aide_t` which has `mlsfilewritetoclr` and `mlsfilereadtoclr`. Our clearance of s15 > s0.
3. Allowed. sysadm_t can execute the file of type `aide_exec_t` and transition to type `aide_t` which has `mlsfilewritetoclr` and `mlsfilereadtoclr`. Our clearance of s15 > s0.