forked from toolshed/abra
54 lines
1.4 KiB
Go
54 lines
1.4 KiB
Go
package userns
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import (
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"bufio"
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"fmt"
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"os"
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"sync"
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)
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var inUserNS = sync.OnceValue(runningInUserNS)
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// runningInUserNS detects whether we are currently running in a user namespace.
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//
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// This code was migrated from [libcontainer/runc] and based on an implementation
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// from [lcx/incus].
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//
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// [libcontainer/runc]: https://github.com/opencontainers/runc/blob/3778ae603c706494fd1e2c2faf83b406e38d687d/libcontainer/userns/userns_linux.go#L12-L49
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// [lcx/incus]: https://github.com/lxc/incus/blob/e45085dd42f826b3c8c3228e9733c0b6f998eafe/shared/util.go#L678-L700
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func runningInUserNS() bool {
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file, err := os.Open("/proc/self/uid_map")
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if err != nil {
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// This kernel-provided file only exists if user namespaces are supported.
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return false
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}
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defer file.Close()
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buf := bufio.NewReader(file)
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l, _, err := buf.ReadLine()
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if err != nil {
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return false
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}
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return uidMapInUserNS(string(l))
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}
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func uidMapInUserNS(uidMap string) bool {
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if uidMap == "" {
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// File exist but empty (the initial state when userns is created,
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// see user_namespaces(7)).
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return true
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}
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var a, b, c int64
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if _, err := fmt.Sscanf(uidMap, "%d %d %d", &a, &b, &c); err != nil {
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// Assume we are in a regular, non user namespace.
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return false
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}
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// As per user_namespaces(7), /proc/self/uid_map of
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// the initial user namespace shows 0 0 4294967295.
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initNS := a == 0 && b == 0 && c == 4294967295
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return !initNS
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}
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