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gofer: open volumes from the initial userns
when gofer can't open them from its user namespace. The gofer namespace can have custom user/group mappings that can prevent it to access volumes. This change repeats the behaviour of runc. If we can't open a volume from the gofer userns, we are trying to open it from the initial userns. For that, we create a small rpc server that the gofer communicates with. Signed-off-by: Andrei Vagin <[email protected]>
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,103 @@ | ||
| // Copyright 2024 The gVisor Authors. | ||
| // | ||
| // Licensed under the Apache License, Version 2.0 (the "License"); | ||
| // you may not use this file except in compliance with the License. | ||
| // You may obtain a copy of the License at | ||
| // | ||
| // http://www.apache.org/licenses/LICENSE-2.0 | ||
| // | ||
| // Unless required by applicable law or agreed to in writing, software | ||
| // distributed under the License is distributed on an "AS IS" BASIS, | ||
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
| // See the License for the specific language governing permissions and | ||
| // limitations under the License. | ||
|
|
||
| package container | ||
|
|
||
| import ( | ||
| "fmt" | ||
| "os" | ||
| "runtime" | ||
| "sync" | ||
|
|
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| specs "github.com/opencontainers/runtime-spec/specs-go" | ||
| "golang.org/x/sys/unix" | ||
| "gvisor.dev/gvisor/pkg/urpc" | ||
| ) | ||
|
|
||
| type openMountRequest struct { | ||
| mount *specs.Mount | ||
| result *OpenMountResult | ||
| done chan error | ||
| } | ||
|
|
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| type goferRPC struct { | ||
| mu sync.Mutex | ||
| openMountRequests chan *openMountRequest | ||
| goferPID int | ||
| } | ||
|
|
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| // OpenMountResult is a result of the rpcp.OpenMount call. | ||
| type OpenMountResult struct { | ||
| urpc.FilePayload | ||
| } | ||
|
|
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| func (rpc *goferRPC) handleRequest(req *openMountRequest) { | ||
| defer close(req.done) | ||
| fd, err := os.OpenFile(req.mount.Source, unix.O_PATH|unix.O_CLOEXEC, 0) | ||
| if err != nil { | ||
| req.done <- err | ||
| return | ||
| } | ||
| req.result.Files = []*os.File{fd} | ||
| } | ||
|
|
||
| func (rpc *goferRPC) openMountLoop() error { | ||
| if err := unix.Unshare(unix.CLONE_FS); err != nil { | ||
| return fmt.Errorf("open mount thread: %w", err) | ||
| } | ||
| nsFd, err := os.Open(fmt.Sprintf("/proc/%d/ns/mnt", rpc.goferPID)) | ||
| if err != nil { | ||
| return fmt.Errorf("open mount thread: open container mntns: %w", err) | ||
| } | ||
| defer nsFd.Close() | ||
| if err := unix.Setns(int(nsFd.Fd()), unix.CLONE_NEWNS); err != nil { | ||
| return fmt.Errorf("open mount thread: join container mntns: %w", err) | ||
| } | ||
| for req := range rpc.openMountRequests { | ||
| rpc.handleRequest(req) | ||
| } | ||
| return nil | ||
| } | ||
|
|
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| // OpenMount is a helper rpc call that a gofer process uses when it can't | ||
| // open/create a mount. | ||
| func (rpc *goferRPC) OpenMount(m *specs.Mount, res *OpenMountResult) error { | ||
| rpc.mu.Lock() | ||
| defer rpc.mu.Unlock() | ||
|
|
||
| if rpc.openMountRequests == nil { | ||
| rpc.openMountRequests = make(chan *openMountRequest) | ||
| go func() { | ||
| // This goroutine holds the current threads forever. It | ||
| // never exits, because child proccesses can set | ||
| // PDEATHSIG. It can't serve other go-routines, because | ||
| // it does unshare CLONE_FS. | ||
| runtime.LockOSThread() | ||
| if err := rpc.openMountLoop(); err != nil { | ||
| for req := range rpc.openMountRequests { | ||
| req.done <- err | ||
| } | ||
| } | ||
| panic("unreachable") | ||
| }() | ||
| } | ||
| req := openMountRequest{ | ||
| mount: m, | ||
| result: res, | ||
| done: make(chan error), | ||
| } | ||
| rpc.openMountRequests <- &req | ||
| err := <-req.done | ||
| return err | ||
| } |