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Fix bwrap loopback permission error in secure mode #21

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nbeerbower wants to merge 2 commits into from
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Fix bwrap loopback permission error in secure mode #21

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3e668c4
Fix bwrap loopback error by removing --unshare-net
claude Jan 14, 2026
d3dffc5
Add user namespace check before enabling secure mode
claude Jan 14, 2026
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19 changes: 13 additions & 6 deletions grove.hml
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Original file line number Diff line number Diff line change
Expand Up @@ -253,12 +253,17 @@ fn load_config() {
// Secure mode - enable bubblewrap sandboxing
let secure = getenv("GROVE_SECURE_MODE");
if (secure != null && (secure == "1" || to_lower(secure) == "true")) {
if (CONFIG["bwrap_available"]) {
CONFIG["secure_mode"] = true;
} else {
if (!CONFIG["bwrap_available"]) {
print("WARNING: GROVE_SECURE_MODE requested but bubblewrap not found");
print(" Install bubblewrap: apt install bubblewrap");
print(" Falling back to basic sandbox mode");
} else if (!check_user_namespaces()) {
print("WARNING: GROVE_SECURE_MODE requested but user namespaces not available");
print(" Enable with: sudo sysctl -w kernel.unprivileged_userns_clone=1");
print(" On Ubuntu 24.04+: sudo sysctl -w kernel.apparmor_restrict_unprivileged_userns=0");
print(" Falling back to basic sandbox mode");
} else {
CONFIG["secure_mode"] = true;
}
}

Expand Down Expand Up @@ -492,11 +497,13 @@ fn build_bwrap_command(temp_file, stdin_file, timeout_sec) {

// Construct bwrap command
// Note: Using bash -c to set ulimits inside the sandbox (sh/dash doesn't support -u)
// Note: We don't use --unshare-net because setting up loopback requires CAP_NET_ADMIN
// which unprivileged users don't have. Network restrictions are handled by
// hemlock's --sandbox flag instead.
let bwrap_cmd = `"${CONFIG["bwrap_path"]}" ` +
// Namespace isolation
`--unshare-user ` +
`--unshare-pid ` +
`--unshare-net ` +
`--unshare-ipc ` +
`--unshare-uts ` +
`--unshare-cgroup ` +
Expand Down Expand Up @@ -651,11 +658,11 @@ fn handle_version() {
fn build_bwrap_check_command(temp_file) {
// Build bubblewrap command for type checking (lighter than execute)
// hemlockc only parses, so we can be more restrictive
// Note: We don't use --unshare-net because setting up loopback requires CAP_NET_ADMIN
let check_cmd = `"${CONFIG["hemlockc_path"]}" --check "${temp_file}"`;

let bwrap_cmd = `"${CONFIG["bwrap_path"]}" ` +
`--unshare-user ` +
`--unshare-net ` +
`--unshare-ipc ` +
`--uid 65534 ` +
`--gid 65534 ` +
Expand Down Expand Up @@ -751,11 +758,11 @@ fn handle_check(body) {

fn build_bwrap_format_command(temp_file) {
// Build bubblewrap command for formatting (needs write access to temp file)
// Note: We don't use --unshare-net because setting up loopback requires CAP_NET_ADMIN
let format_cmd = `"${CONFIG["hemlock_path"]}" format "${temp_file}"`;

let bwrap_cmd = `"${CONFIG["bwrap_path"]}" ` +
`--unshare-user ` +
`--unshare-net ` +
`--unshare-ipc ` +
`--uid 65534 ` +
`--gid 65534 ` +
Expand Down