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5cd5ffcc50
Change logic of bounds checking to match kernel's bound checking. The following explanation is taken from Stephen Smalley's kernel patch. Under the new logic, if the source type and target types are both bounded, then the parent of the source type must be allowed the same permissions to the parent of the target type. If only the source type is bounded, then the parent of the source type must be allowed the same permissions to the target type. Examples of the new logic and comparisons with the old logic: 1. If we have: typebounds A B; then: allow B self:process <permissions>; will satisfy the bounds constraint iff: allow A self:process <permissions>; is also allowed in policy. Under the old logic, the allow rule on B satisfies the bounds constraint if any of the following three are allowed: allow A B:process <permissions>; or allow B A:process <permissions>; or allow A self:process <permissions>; However, either of the first two ultimately require the third to satisfy the bounds constraint under the old logic, and therefore this degenerates to the same result (but is more efficient - we only need to perform one compute_av call). 2. If we have: typebounds A B; typebounds A_exec B_exec; then: allow B B_exec:file <permissions>; will satisfy the bounds constraint iff: allow A A_exec:file <permissions>; is also allowed in policy. This is essentially the same as #1; it is merely included as an example of dealing with object types related to a bounded domain in a manner that satisfies the bounds relationship. Note that this approach is preferable to leaving B_exec unbounded and having: allow A B_exec:file <permissions>; in policy because that would allow B's entrypoints to be used to enter A. Similarly for _tmp or other related types. 3. If we have: typebounds A B; and an unbounded type T, then: allow B T:file <permissions>; will satisfy the bounds constraint iff: allow A T:file <permissions>; is allowed in policy. The old logic would have been identical for this example. 4. If we have: typebounds A B; and an unbounded domain D, then: allow D B:unix_stream_socket <permissions>; is not subject to any bounds constraints under the new logic because D is not bounded. This is desirable so that we can allow a domain to e.g. connectto a child domain without having to allow it to do the same to its parent. The old logic would have required: allow D A:unix_stream_socket <permissions>; to also be allowed in policy. Signed-off-by: James Carter <jwcart2@tycho.nsa.gov> |
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