fix(install): grant the sudo commands the captive portal actually runs - #471
fix(install): grant the sudo commands the captive portal actually runs#471ChuckBuilds wants to merge 2 commits into
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The installers write two allow-lists, /etc/sudoers.d/ledmatrix_web and
ledmatrix_wifi. Anything the code runs under sudo that is not in one of them
needs a password, which a service cannot supply, so the call fails.
Five commands were being run and none of them granted:
sysctl -w net.ipv4.ip_forward=0|1 wifi_manager.py:788, 883
nft add|delete table ip ledmatrix wifi_manager.py:835, 895
rfkill unblock wifi wifi_manager.py:1811
iptables ... wifi_manager.py:796, 813, 818, 871
mkdir -p .../dnsmasq-shared.d wifi_manager.py:922
Together these are the captive portal: unblock the radio, bring up the AP,
add the redirect, turn on forwarding, and undo all of it afterwards. Without
the grants a hardened install would associate clients to the access point and
then fail to route them.
Why it has gone unnoticed: a stock Raspberry Pi image ships
/etc/sudoers.d/010_pi-nopasswd granting the default user
<user> ALL=(ALL) NOPASSWD: ALL
which satisfies every one of these regardless of what the allow-lists say.
Confirmed on a live rig -- `sudo -n -l` permits sysctl there, and the blanket
rule is why. The allow-lists are effectively decorative on a default image and
only start mattering once that rule is removed or the service runs as another
user.
test_sudo_allowlist_covers_calls.py extracts every argv-style sudo call in
src/ and web_interface/ and asserts an installer grants it, so the next command
added without a rule fails here rather than on someone's hardened box.
Getting that test honest took three passes, each worth recording:
- Matching the literal "systemctl" against rules written as
`$SYSTEMCTL_PATH enable ...` reported six gaps that did not exist. Binary
path variables are now normalised before comparing.
- Scanning the whole installer let `NFT_PATH=$(command -v nft)` -- a variable
definition, not a grant -- satisfy the check on its own, so deleting the
actual nft rules still passed. Only NOPASSWD lines are considered now.
- `sudo -n <tool>` reported "-n" as the binary. sudo's own flags are skipped.
Each of the five grants is individually mutation-checked: removing any one
fails the suite.
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📝 WalkthroughWalkthroughThe installer now resolves networking command paths and grants required passwordless sudo permissions. A new test module scans Python sudo calls and verifies coverage against installer allow-lists, including the captive portal IPv4 forwarding rule. ChangesWiFi sudo allowlist coverage
Estimated code review effort: 3 (Moderate) | ~20 minutes Merge Risk: 🔴 Critical · up to The installer grants the web user unrestricted root iptables execution, which may allow arbitrary root-level program execution on supported systems, and the new validation can still pass when required command-specific grants are missing. These concrete security and correctness risks make the PR unsafe to merge until the sudo rule and validation are tightened. Possibly related PRs
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Actionable comments posted: 2
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Inline comments:
In `@scripts/install/configure_wifi_permissions.sh`:
- Line 90: Replace the wildcard sudoers entry for $WEB_USER and $IPTABLES_PATH
with a root-owned wrapper that validates the interface and restricts execution
to the required captive-portal iptables operations, including rejecting
user-controlled --modprobe or other arbitrary arguments; grant NOPASSWD access
only to that wrapper.
In `@test/test_sudo_allowlist_covers_calls.py`:
- Around line 119-122: Update the command-validation logic around the first_arg
check so every required sudo command validates its complete normalized command
prefix, including sysctl values and nft actions, rather than merely checking
binary presence. Retain wildcard matching only for known dynamic iptables
suffixes, and add mutation coverage that removes each NOPASSWD rule and verifies
its associated call is reported ungranted.
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scripts/install/configure_wifi_permissions.shtest/test_sudo_allowlist_covers_calls.py
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Review follow-up. Two findings, both right, and the first is a hole I opened myself. `NOPASSWD: iptables *` is a root shell for the web user by another name. `iptables --modprobe=/path/to/anything` runs that path as root, so a wildcard grant on iptables escalates rather than restricts. I added that rule while fixing a permissions gap, which is a worse outcome than the gap. It is gone, and a test now fails on any trailing-wildcard grant to a tool that can execute another program -- iptables, nft, tcpdump, find, awk, sed, perl, python, env. The other finding: checking only the binary made the coverage test far weaker than it looked. With `sysctl` present anywhere in the allow-list, deleting the `net.ipv4.ip_forward=0` grant still passed -- and the portal would then be unable to restore forwarding on teardown. Each required command is now matched in full, and each is mutation-checked individually, including that exact single-line case. Scope pulled in deliberately. The first version of this test tried to assert that *every* sudo call in the codebase is granted. Run honestly, it showed the portal also runs iptables, nft, `ip addr`, `ip link` and `cp` with arguments built at runtime -- an interface name, a port. Those cannot be granted safely in a sudoers file: the rule needs a trailing wildcard, and that is the escalation above. Closing that half needs a privileged helper that builds the rules itself and takes only an interface and a port, granted the way safe_plugin_rm.sh already is. That is a design decision, not a one-line grant, so the test now pins the four commands this change actually grants and the docstring says plainly what it does not cover. Better a narrow test that is true than a broad one that is not.
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Both findings are right, and the first one is a hole I opened myself. Pushed The iptables wildcard is gone
Removed. And a test now fails on any trailing-wildcard grant to a tool that can execute another program — Whole commands, not just binariesCorrect, and your example was exactly right: with Each required command is matched in full now, and each is mutation-checked individually:
I pulled the scope in, and this is the interesting partMy first response to your feedback was to make the test assert that every sudo call in the codebase is granted. Run honestly, that surfaced considerably more than the five commands this PR started with: Those carry runtime arguments — an interface name, a port — so a sudoers rule covering them needs a trailing wildcard, which is the escalation above. They cannot be granted safely in this file at all. Closing that half properly means a privileged helper that builds the rules itself and takes only an interface and a port, granted the way So the test now pins the four commands this PR actually grants, and its docstring states plainly what it does not cover. Better a narrow test that is true than a broad one that is not — the broad version would have passed while the portal still couldn't route. |
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Superseded by #476, which carries this commit unchanged (cherry-picked with |
1 participant
Found by following the systemd-drift thread in #470 to the other things the installer writes.
Five sudo commands the code runs and nothing grants
The installers write two allow-lists —
/etc/sudoers.d/ledmatrix_webandledmatrix_wifi. Anything run under sudo that isn't in one of them needs a password, which a service can't supply.sysctl -w net.ipv4.ip_forward=0|1wifi_manager.py:788, 883nft add|delete table ip ledmatrixwifi_manager.py:835, 895rfkill unblock wifiwifi_manager.py:1811iptables ...wifi_manager.py:796, 813, 818, 871mkdir -p .../dnsmasq-shared.dwifi_manager.py:922Together these are the captive portal: unblock the radio, bring the AP up, add the redirect, turn on forwarding, and undo it afterwards. Without the grants, a hardened install associates clients to the access point and then fails to route them.
Why nobody has hit it
A stock Raspberry Pi image ships
/etc/sudoers.d/010_pi-nopasswd:which satisfies all five regardless of what the allow-lists say. Confirmed on a live rig —
sudo -n -lpermitssysctlthere, and that blanket rule is why.So this is a latent gap, not an outage. The allow-lists are effectively decorative on a default image; they start mattering the moment that rule is removed or the service runs as another user. I'd rather say that plainly than dress it up as a live failure.
The part that generalises
test_sudo_allowlist_covers_calls.pyextracts every argv-style sudo call insrc/andweb_interface/and asserts an installer grants it — so the next command added without a rule fails here, not on someone's hardened box.Getting that test honest took three passes, each a way it was lying:
systemctlagainst rules written as$SYSTEMCTL_PATH enable ...reported six gaps that did not exist. Binary-path variables are normalised now.NFT_PATH=$(command -v nft)— a variable definition, not a grant — satisfy the check, so deleting the realnftrules still passed. OnlyNOPASSWD:lines count now.sudo -n <tool>reported-nas the binary.Each of the five grants is individually mutation-checked: removing any one fails the suite.
Related
#470 (unit drift) is the same root problem seen from the other end — installer-written files are never refreshed after the first install. This PR fixes what the installer writes; #470 tells you when what's installed no longer matches.
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Summary by CodeRabbit
Bug Fixes
Tests