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alloc fs: use case-insensitive check for reads of secret/private dir
When using the Client FS APIs, we check to ensure that reads don't traverse into the allocation's secret dir and private dir. But this check can be bypassed on case-insensitive file systems (ex. Windows, macOS, and Linux with obscure ext4 options enabled). This allows a user with `read-fs` permissions but not `alloc-exec` permissions to read from the secrets dir. This changeset updates the check so that it's case-insensitive. This risks false positives for escape (see linked Go issue), but only if a task without filesystem isolation deliberately writes into the task working directory to do so, which is a fail-safe failure mode. Ref: golang/go#18358
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```release-note:security | ||
security: Fixed a bug in client FS API where the check to prevent reads from the secrets dir could be bypassed on case-insensitive file systems | ||
``` |
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// Copyright (c) HashiCorp, Inc. | ||
// SPDX-License-Identifier: BUSL-1.1 | ||
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//go:build !linux | ||
// +build !linux | ||
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package allocdir | ||
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import ( | ||
"os" | ||
"path/filepath" | ||
"testing" | ||
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"github.com/hashicorp/nomad/ci" | ||
"github.com/hashicorp/nomad/helper/testlog" | ||
"github.com/hashicorp/nomad/nomad/structs" | ||
"github.com/hashicorp/nomad/plugins/drivers/fsisolation" | ||
"github.com/shoenig/test/must" | ||
) | ||
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func TestAllocDir_ReadAt_CaseInsensitiveSecretDir(t *testing.T) { | ||
ci.Parallel(t) | ||
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// On macOS, os.TempDir returns a symlinked path under /var which | ||
// is outside of the directories shared into the VM used for Docker. | ||
// Expand the symlink to get the real path in /private, which is ok. | ||
tmp, err := filepath.EvalSymlinks(t.TempDir()) | ||
must.NoError(t, err) | ||
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d := NewAllocDir(testlog.HCLogger(t), tmp, tmp, "test") | ||
must.NoError(t, d.Build()) | ||
defer func() { _ = d.Destroy() }() | ||
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td := d.NewTaskDir(t1Windows) | ||
must.NoError(t, td.Build(fsisolation.None, nil, "nobody")) | ||
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target := filepath.Join(t1Windows.Name, TaskSecrets, "test_file") | ||
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full := filepath.Join(d.AllocDir, target) | ||
must.NoError(t, os.WriteFile(full, []byte("hi"), 0o600)) | ||
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targetCaseInsensitive := filepath.Join(t1Windows.Name, "sEcReTs", "test_file") | ||
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_, err = d.ReadAt(targetCaseInsensitive, 0) | ||
must.EqError(t, err, "Reading secret file prohibited: "+targetCaseInsensitive) | ||
} | ||
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var ( | ||
t1Windows = &structs.Task{ | ||
Name: "web", | ||
Driver: "exec", | ||
Config: map[string]interface{}{ | ||
"command": "/bin/date", | ||
"args": "+%s", | ||
}, | ||
Resources: &structs.Resources{ | ||
DiskMB: 1, | ||
}, | ||
} | ||
) |
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