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Procfs mounts used a per-mount major number for /proc/gvisor/checkpoint. Since Linux reserves a limited number of dynamic major numbers, running many isolated container actions concurrently would exhaust the pool and crash the sentry with EBUSY. This adds VFS.GetSharedDynamicCharDevMajor(key) to allocate a major on first use and share it across all subsequent mounts for that key. The sentry now consumes exactly two majors for these devices regardless of how many procfs instances are mounted. PiperOrigin-RevId: 967985107
68 lines
2.3 KiB
Go
68 lines
2.3 KiB
Go
// Copyright 2026 The gVisor Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package vfs
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import (
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"testing"
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"gvisor.dev/gvisor/pkg/sentry/contexttest"
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)
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func TestGetSharedDynamicCharDevMajor(t *testing.T) {
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ctx := contexttest.Context(t)
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vfsObj := &VirtualFilesystem{}
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if err := vfsObj.Init(ctx); err != nil {
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t.Fatalf("VFS init: %v", err)
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}
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first, err := vfsObj.GetSharedDynamicCharDevMajor(CheckpointDeviceMajorKey)
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if err != nil {
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t.Fatalf("GetSharedDynamicCharDevMajor(%d) failed: %v", CheckpointDeviceMajorKey, err)
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}
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// Repeated allocations for the same key must return the same major number
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// without consuming additional ones; in particular, many more allocations
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// than the number of dynamic major numbers available must succeed.
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for i := 0; i < 1000; i++ {
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got, err := vfsObj.GetSharedDynamicCharDevMajor(CheckpointDeviceMajorKey)
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if err != nil {
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t.Fatalf("GetSharedDynamicCharDevMajor(%d) failed after %d calls: %v", CheckpointDeviceMajorKey, i+1, err)
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}
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if got != first {
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t.Fatalf("GetSharedDynamicCharDevMajor(%d) = %d, want %d", CheckpointDeviceMajorKey, got, first)
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}
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}
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// Distinct keys must get distinct major numbers.
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second, err := vfsObj.GetSharedDynamicCharDevMajor(FSCheckpointDeviceMajorKey)
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if err != nil {
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t.Fatalf("GetSharedDynamicCharDevMajor(%d) failed: %v", FSCheckpointDeviceMajorKey, err)
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}
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if second == first {
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t.Errorf("GetSharedDynamicCharDevMajor(%d) = %d, want != %d", FSCheckpointDeviceMajorKey, second, first)
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}
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// Shared major numbers must not be handed out by
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// GetDynamicCharDevMajor().
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for {
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major, err := vfsObj.GetDynamicCharDevMajor()
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if err != nil {
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break
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}
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if major == first || major == second {
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t.Fatalf("GetDynamicCharDevMajor() = %d, which is already reserved for a shared key", major)
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}
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}
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}
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