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fix(drop-sudo): use the shell test builtin for the socket ACL check #191

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fix(drop-sudo): use the shell test builtin for the socket ACL check #191

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8 changes: 5 additions & 3 deletions dist/main.js
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8 changes: 6 additions & 2 deletions src/dropSudo.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -456,15 +456,19 @@ async function isSocketWritable(
identity.supplementaryGroupIds.length === 0
? "--clear-groups"
: `--groups=${identity.supplementaryGroupIds.join(",")}`;
// The shell's test builtin asks the kernel (faccessat), which applies ACLs.
// The uutils /usr/bin/test on Ubuntu 26.04 only reads the mode bits.
const result = await execCommand(
"/usr/bin/setpriv",
[
`--reuid=${credentials.userId}`,
`--regid=${identity.primaryGroupId}`,
groupArgument,
"--",
"/usr/bin/test",
"-w",
"/bin/sh",
"-c",
'test -w "$1"',
"sh",
"/proc/self/fd/3",
],
{
Expand Down
27 changes: 12 additions & 15 deletions test/dropSudo.test.mjs
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Original file line number Diff line number Diff line change
Expand Up @@ -25,6 +25,11 @@ const canTestSocketAcls =
canTestLinuxIsolation &&
spawnSync("/usr/bin/setfacl", ["--version"], { stdio: "ignore" }).status === 0;

// The uutils test on Ubuntu 26.04 ignores ACLs; the shell builtin asks the kernel.
function testWritable(target) {
return ["/bin/sh", "-c", 'test -w "$1"', "sh", target];
}

function sudo(args, options = {}) {
const result = spawnSync("sudo", ["-n", "--", ...args], {
encoding: "utf8",
Expand Down Expand Up @@ -345,17 +350,15 @@ test(
...(canTestSocketAcls ? [namedUserAclSocket] : []),
...(canTestSocketAcls && scenario.staleGroups ? [staleAclSocket] : []),
]) {
sudo(["/usr/bin/sudo", "-n", "-u", user, "--", "test", "-w", socket]);
sudo(["/usr/bin/sudo", "-n", "-u", user, "--", ...testWritable(socket)]);
}
assert.notEqual(
spawnSync("sudo", [
"-n",
"-u",
user,
"--",
"test",
"-w",
fallbackSocket,
...testWritable(fallbackSocket),
]).status,
0
);
Expand All @@ -366,9 +369,7 @@ test(
"-u",
user,
"--",
"test",
"-w",
fallbackAclSocket,
...testWritable(fallbackAclSocket),
]).status,
0
);
Expand All @@ -378,9 +379,7 @@ test(
`--regid=${safeGroup}`,
"--clear-groups",
"--",
"/usr/bin/test",
"-w",
fallbackAclSocket,
...testWritable(fallbackAclSocket),
]);
}

Expand Down Expand Up @@ -529,7 +528,7 @@ fs.writeFileSync(${JSON.stringify(originalCredentialsPath)}, JSON.stringify({
? [
...command.slice(0, 4),
"/bin/sh", "-ec",
'/usr/bin/sudo -n /usr/bin/gpasswd -d "$1" "$2"; /usr/bin/id -G > "$3"; /usr/bin/sudo -n -u "$1" -- /usr/bin/test -w "$4"; shift 4; exec "$@"',
'/usr/bin/sudo -n /usr/bin/gpasswd -d "$1" "$2"; /usr/bin/id -G > "$3"; /usr/bin/sudo -n -u "$1" -- /bin/sh -c \'test -w "$1"\' sh "$4"; shift 4; exec "$@"',
"codex-stale-groups", user, privilegedGroup, liveGroupsPath, shadowSocket,
...command.slice(4),
]
Expand Down Expand Up @@ -739,9 +738,7 @@ fs.writeFileSync(${JSON.stringify(originalCredentialsPath)}, JSON.stringify({
"-u",
user,
"--",
"test",
"-w",
socket,
...testWritable(socket),
]);
assert.notEqual(access.status, 0);
const originalAccess = spawnSync("sudo", [
Expand All @@ -751,7 +748,7 @@ fs.writeFileSync(${JSON.stringify(originalCredentialsPath)}, JSON.stringify({
originalCredentials.supplementaryGroupIds.length === 0
? "--clear-groups"
: `--groups=${originalCredentials.supplementaryGroupIds.join(",")}`,
"--", "/usr/bin/test", "-w", socket,
"--", ...testWritable(socket),
], { encoding: "utf8", timeout: 5_000 });
assert.equal(originalAccess.status, 1,
`original runner credentials retained access to ${socket}: ${originalAccess.stderr}`);
Expand Down
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