fix(deploy-substrate): move boundary-gated IAM policy off the role's inline budget

The first deploy of seahaven-deploy-substrate failed in both prod and dev
with ServiceLimitExceeded: 'Maximum policy size of 10240 bytes exceeded
for role github-cfn-execution-role'. The role's inline policies already
sat ~94 bytes under IAM's hard 10,240-byte per-role limit, so the two
Deny statements added to close the boundary-removal escalation did not
fit (10,656 total).

Moves the whole boundary-gated IAM block (6 Allow + 2 Deny statements)
into an attached managed policy, which carries its own separate
6,144-byte budget. Inline drops to 8,285 with ~1.9 KB of headroom;
the managed policy sits at 2,371.

Effective permissions are unchanged: the union of role statements
(inline + attached) is byte-identical as a sorted set before and after
the move (27 statements both sides), identity policies are unioned, and
an explicit Deny still wins. Boundary and trust policy untouched.

Both failed stacks rolled back cleanly with zero orphaned resources and
were deleted before this retry.
This commit is contained in:
Adam Moussa 2026-07-27 16:43:15 -04:00
parent e898cb6342
commit 2cfc122269
No known key found for this signature in database
2 changed files with 170 additions and 132 deletions

View file

@ -21,7 +21,10 @@ export interface DeploySubstrateStackProps extends cdk.StackProps {
* - `seahaven-lambda-execution-boundary` permissions boundary (the ceiling
* applied to every SAM-generated Lambda execution role),
* - `github-cfn-execution-role` (the shared CloudFormation execution role
* that cd-sam callers pass as cfn-role-arn).
* that cd-sam callers pass as cfn-role-arn), plus
* `seahaven-cfn-exec-iam-management`, the attached managed policy holding
* that role's boundary-gated IAM statements (separated from the inline
* policies to stay under IAM's 10,240-byte per-role inline limit).
*
* Deliberately NOT here: per-repo githubdeploy-* roles. Those are provisioned
* per repo at migration/onboarding time (deploy-role-first playbook) so an

View file

@ -23,6 +23,15 @@ Description: >-
# for mgmt where both resources already exist, so mgmt's copy is
# deliberately unchanged),
# - DeletionPolicy/UpdateReplacePolicy Retain on the OIDC provider,
# - the boundary-gated IAM block moved from an INLINE role policy into an
# attached managed policy (SamCfnIamManagementPolicy). Forced by IAM's
# 10,240-byte per-role inline limit: mgmt's inline set is ~10.1 KB, i.e.
# ~94 bytes from the cap, so the added Deny statements did not fit and the
# first deploy failed with ServiceLimitExceeded (2026-07-27). Effective
# permissions are unchanged — verified by comparing the full 27-statement
# set before and after the move (identical), since identity policies are
# unioned and an explicit Deny still wins. NOTE for the mgmt remediation:
# mgmt needs this same restructure before its Deny statements can be added,
# - SECURITY FIX, deliberate divergence: iam:DeleteRolePermissionsBoundary
# removed from Sid IAMPutPermissionsBoundary and explicit Deny statements
# (DenyBoundaryTampering / DenyBoundaryPolicyEdit) added. The mgmt copy
@ -319,6 +328,8 @@ Resources:
DependsOn: LambdaExecutionBoundary
Properties:
RoleName: github-cfn-execution-role
ManagedPolicyArns:
- !Ref SamCfnIamManagementPolicy
AssumeRolePolicyDocument:
Version: "2012-10-17"
Statement:
@ -751,142 +762,166 @@ Resources:
- wafv2:ListResourcesForWebACL
Resource: "*"
# ── IAM role lifecycle — BOUNDARY-GATED ──────────────────────────
# This is the PRIMARY escalation control for INFRA-97.
#
# iam:CreateRole / iam:AttachRolePolicy / iam:PutRolePolicy are
# conditioned on iam:PermissionsBoundary StringEquals the
# seahaven-lambda-execution-boundary ARN. That condition means
# any role this execution role creates must have the boundary
# applied, so it can never exceed what the boundary allows
# (which is scoped to the services the five stacks actually use).
#
# iam:PassRole is also included here so CloudFormation can pass
# the auto-generated Lambda execution role to the Lambda service.
#
# Why not path-scoped (e.g. iam:ResourceTag / path /cfn-managed/)?
# SAM's AWS::Serverless::Function auto-generates execution roles at
# path / — there is no supported way to set a custom RolePath on
# SAM auto-roles. A path condition would therefore exclude the
# SAM auto-roles and break every deploy. The PermissionsBoundary
# condition achieves the same security goal without a path requirement.
- PolicyName: iam-role-management-boundary-gated
PolicyDocument:
Version: "2012-10-17"
Statement:
# Create role — MUST attach boundary
- Sid: IAMCreateRoleWithBoundary
Effect: Allow
Action:
- iam:CreateRole
Resource:
- !Sub "arn:aws:iam::${AWS::AccountId}:role/*"
Condition:
StringEquals:
"iam:PermissionsBoundary": !Sub "arn:aws:iam::${AWS::AccountId}:policy/seahaven-lambda-execution-boundary"
# ---------------------------------------------------------------------------
# IAM role lifecycle - BOUNDARY-GATED (attached managed policy)
#
# Lives in a MANAGED policy, not inline on the role, because the role's
# inline policies total ~10.1 KB against IAM's hard 10,240-byte per-role
# inline limit - adding the Deny statements below inline exceeds it and
# fails the deploy (ServiceLimitExceeded, hit live 2026-07-27). Attached
# managed policies have their own separate 6,144-byte budget, so moving this
# block out both fits the Denies and leaves ~1.9 KB of inline headroom for
# future statements. Identity policies are unioned and an explicit Deny still
# wins, so effective permissions are unchanged by the relocation.
#
# This is the PRIMARY escalation control for INFRA-97.
#
# iam:CreateRole / iam:AttachRolePolicy / iam:PutRolePolicy are
# conditioned on iam:PermissionsBoundary StringEquals the
# seahaven-lambda-execution-boundary ARN. That condition means
# any role this execution role creates must have the boundary
# applied, so it can never exceed what the boundary allows
# (which is scoped to the services the five stacks actually use).
#
# iam:PassRole is also included here so CloudFormation can pass
# the auto-generated Lambda execution role to the Lambda service.
#
# Why not path-scoped (e.g. iam:ResourceTag / path /cfn-managed/)?
# SAM's AWS::Serverless::Function auto-generates execution roles at
# path / — there is no supported way to set a custom RolePath on
# SAM auto-roles. A path condition would therefore exclude the
# SAM auto-roles and break every deploy. The PermissionsBoundary
# condition achieves the same security goal without a path requirement.
# ---------------------------------------------------------------------------
SamCfnIamManagementPolicy:
Type: AWS::IAM::ManagedPolicy
Properties:
# Fixed name: changing it makes CloudFormation create a replacement policy
# and detach this one, which briefly drops the role's IAM permissions
# mid-update. Treat a rename as a coordinated migration, not an edit. This
# is the role's FIRST attached managed policy (per-role quota is 10).
ManagedPolicyName: seahaven-cfn-exec-iam-management
Description: >-
Boundary-gated IAM role lifecycle for github-cfn-execution-role, plus the
explicit Deny backstops that keep the permissions boundary from being
detached or rewritten. Separated from the role's inline policies to stay
under IAM's 10,240-byte inline limit.
PolicyDocument:
Version: "2012-10-17"
Statement:
# Create role — MUST attach boundary
- Sid: IAMCreateRoleWithBoundary
Effect: Allow
Action:
- iam:CreateRole
Resource:
- !Sub "arn:aws:iam::${AWS::AccountId}:role/*"
Condition:
StringEquals:
"iam:PermissionsBoundary": !Sub "arn:aws:iam::${AWS::AccountId}:policy/seahaven-lambda-execution-boundary"
# Attach managed policies — MUST have boundary already on role
- Sid: IAMAttachPolicyWithBoundary
Effect: Allow
Action:
- iam:AttachRolePolicy
Resource:
- !Sub "arn:aws:iam::${AWS::AccountId}:role/*"
Condition:
StringEquals:
"iam:PermissionsBoundary": !Sub "arn:aws:iam::${AWS::AccountId}:policy/seahaven-lambda-execution-boundary"
# Attach managed policies — MUST have boundary already on role
- Sid: IAMAttachPolicyWithBoundary
Effect: Allow
Action:
- iam:AttachRolePolicy
Resource:
- !Sub "arn:aws:iam::${AWS::AccountId}:role/*"
Condition:
StringEquals:
"iam:PermissionsBoundary": !Sub "arn:aws:iam::${AWS::AccountId}:policy/seahaven-lambda-execution-boundary"
# Put inline policy — MUST have boundary already on role
- Sid: IAMPutRolePolicyWithBoundary
Effect: Allow
Action:
- iam:PutRolePolicy
Resource:
- !Sub "arn:aws:iam::${AWS::AccountId}:role/*"
Condition:
StringEquals:
"iam:PermissionsBoundary": !Sub "arn:aws:iam::${AWS::AccountId}:policy/seahaven-lambda-execution-boundary"
# Put inline policy — MUST have boundary already on role
- Sid: IAMPutRolePolicyWithBoundary
Effect: Allow
Action:
- iam:PutRolePolicy
Resource:
- !Sub "arn:aws:iam::${AWS::AccountId}:role/*"
Condition:
StringEquals:
"iam:PermissionsBoundary": !Sub "arn:aws:iam::${AWS::AccountId}:policy/seahaven-lambda-execution-boundary"
# Boundary management — SET the boundary only. DELETE is NOT
# granted: for a delete, the iam:PermissionsBoundary condition key
# reflects the boundary CURRENTLY attached to the target role, so
# a StringEquals condition on the boundary ARN MATCHES exactly the
# roles the gate protects. Granting delete under that condition
# lets this role create a boundary-gated role with an inline *:*
# policy, strip the boundary, and pass the now-unbounded role to
# Lambda — defeating the primary escalation control. Verified live
# against the mgmt copy 2026-07-27 (simulate-principal-policy:
# iam:DeleteRolePermissionsBoundary = allowed). SAM never needs
# the delete: it only SETS the boundary on roles it creates, and
# stack teardown calls DeleteRole, not DeleteRolePermissionsBoundary.
- Sid: IAMPutPermissionsBoundary
Effect: Allow
Action:
- iam:PutRolePermissionsBoundary
Resource:
- !Sub "arn:aws:iam::${AWS::AccountId}:role/*"
Condition:
StringEquals:
"iam:PermissionsBoundary": !Sub "arn:aws:iam::${AWS::AccountId}:policy/seahaven-lambda-execution-boundary"
# Boundary management — SET the boundary only. DELETE is NOT
# granted: for a delete, the iam:PermissionsBoundary condition key
# reflects the boundary CURRENTLY attached to the target role, so
# a StringEquals condition on the boundary ARN MATCHES exactly the
# roles the gate protects. Granting delete under that condition
# lets this role create a boundary-gated role with an inline *:*
# policy, strip the boundary, and pass the now-unbounded role to
# Lambda — defeating the primary escalation control. Verified live
# against the mgmt copy 2026-07-27 (simulate-principal-policy:
# iam:DeleteRolePermissionsBoundary = allowed). SAM never needs
# the delete: it only SETS the boundary on roles it creates, and
# stack teardown calls DeleteRole, not DeleteRolePermissionsBoundary.
- Sid: IAMPutPermissionsBoundary
Effect: Allow
Action:
- iam:PutRolePermissionsBoundary
Resource:
- !Sub "arn:aws:iam::${AWS::AccountId}:role/*"
Condition:
StringEquals:
"iam:PermissionsBoundary": !Sub "arn:aws:iam::${AWS::AccountId}:policy/seahaven-lambda-execution-boundary"
# Explicit Deny backstop (AWS's documented NoBoundaryPolicyEdit /
# NoBoundaryDelete delegation pattern). A Deny is required, not
# merely omitting the Allow: without it, any future Allow added to
# this role — or a broader managed policy attached to it — silently
# reopens the escalation. Covers both removing a boundary from a
# role and rewriting the boundary POLICY DOCUMENT itself (the
# latter is only implicitly denied today).
- Sid: DenyBoundaryTampering
Effect: Deny
Action:
- iam:DeleteRolePermissionsBoundary
- iam:DeleteUserPermissionsBoundary
Resource:
- !Sub "arn:aws:iam::${AWS::AccountId}:role/*"
- !Sub "arn:aws:iam::${AWS::AccountId}:user/*"
# Explicit Deny backstop (AWS's documented NoBoundaryPolicyEdit /
# NoBoundaryDelete delegation pattern). A Deny is required, not
# merely omitting the Allow: without it, any future Allow added to
# this role — or a broader managed policy attached to it — silently
# reopens the escalation. Covers both removing a boundary from a
# role and rewriting the boundary POLICY DOCUMENT itself (the
# latter is only implicitly denied today).
- Sid: DenyBoundaryTampering
Effect: Deny
Action:
- iam:DeleteRolePermissionsBoundary
- iam:DeleteUserPermissionsBoundary
Resource:
- !Sub "arn:aws:iam::${AWS::AccountId}:role/*"
- !Sub "arn:aws:iam::${AWS::AccountId}:user/*"
- Sid: DenyBoundaryPolicyEdit
Effect: Deny
Action:
- iam:CreatePolicyVersion
- iam:SetDefaultPolicyVersion
- iam:DeletePolicyVersion
- iam:DeletePolicy
Resource:
- !Sub "arn:aws:iam::${AWS::AccountId}:policy/seahaven-lambda-execution-boundary"
- Sid: DenyBoundaryPolicyEdit
Effect: Deny
Action:
- iam:CreatePolicyVersion
- iam:SetDefaultPolicyVersion
- iam:DeletePolicyVersion
- iam:DeletePolicy
Resource:
- !Sub "arn:aws:iam::${AWS::AccountId}:policy/seahaven-lambda-execution-boundary"
# Read / tag / delete role and policy — no boundary condition needed
- Sid: IAMRoleReadAndDelete
Effect: Allow
Action:
- iam:DeleteRole
- iam:DeleteRolePolicy
- iam:DetachRolePolicy
- iam:GetRole
- iam:GetRolePolicy
- iam:ListAttachedRolePolicies
- iam:ListRolePolicies
- iam:ListRoles
- iam:TagRole
- iam:UntagRole
- iam:UpdateRole
- iam:UpdateRoleDescription
- iam:UpdateAssumeRolePolicy
- iam:GetPolicy
- iam:GetPolicyVersion
- iam:ListPolicies
- iam:ListPolicyVersions
Resource: "*"
# Read / tag / delete role and policy — no boundary condition needed
- Sid: IAMRoleReadAndDelete
Effect: Allow
Action:
- iam:DeleteRole
- iam:DeleteRolePolicy
- iam:DetachRolePolicy
- iam:GetRole
- iam:GetRolePolicy
- iam:ListAttachedRolePolicies
- iam:ListRolePolicies
- iam:ListRoles
- iam:TagRole
- iam:UntagRole
- iam:UpdateRole
- iam:UpdateRoleDescription
- iam:UpdateAssumeRolePolicy
- iam:GetPolicy
- iam:GetPolicyVersion
- iam:ListPolicies
- iam:ListPolicyVersions
Resource: "*"
# PassRole — CloudFormation passes the Lambda execution role
# to the Lambda service. Scoped to SAM-generated role pattern.
- Sid: IAMPassRole
Effect: Allow
Action:
- iam:PassRole
Resource:
- !Sub "arn:aws:iam::${AWS::AccountId}:role/*"
Condition:
StringEquals:
"iam:PassedToService": "lambda.amazonaws.com"
# PassRole — CloudFormation passes the Lambda execution role
# to the Lambda service. Scoped to SAM-generated role pattern.
- Sid: IAMPassRole
Effect: Allow
Action:
- iam:PassRole
Resource:
- !Sub "arn:aws:iam::${AWS::AccountId}:role/*"
Condition:
StringEquals:
"iam:PassedToService": "lambda.amazonaws.com"