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aaf5254e26
The old version was taken from an MPL-licensed library. This is a cleanroom implementation. The code is shorter and it's now explicit that only Linux ACLs are supported.
89 lines
2.0 KiB
Go
89 lines
2.0 KiB
Go
package dump
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import (
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"encoding/binary"
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"errors"
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"strconv"
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)
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const (
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// Permissions
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aclPermRead = 0x4
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aclPermWrite = 0x2
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aclPermExecute = 0x1
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// Tags
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aclTagUserObj = 0x01 // Owner.
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aclTagUser = 0x02
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aclTagGroupObj = 0x04 // Owning group.
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aclTagGroup = 0x08
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aclTagMask = 0x10
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aclTagOther = 0x20
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)
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// formatLinuxACL converts a Linux ACL from its binary format to the POSIX.1e
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// long text format.
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//
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// User and group IDs are printed in decimal, because we may be dumping
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// a snapshot from a different machine.
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//
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// https://man7.org/linux/man-pages/man5/acl.5.html
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// https://savannah.nongnu.org/projects/acl
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// https://simson.net/ref/1997/posix_1003.1e-990310.pdf
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func formatLinuxACL(acl []byte) (string, error) {
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if len(acl)-4 < 0 || (len(acl)-4)%8 != 0 {
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return "", errors.New("wrong length")
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}
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version := binary.LittleEndian.Uint32(acl)
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if version != 2 {
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return "", errors.New("unsupported ACL format version")
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}
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acl = acl[4:]
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text := make([]byte, 0, 2*len(acl))
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for ; len(acl) >= 8; acl = acl[8:] {
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tag := binary.LittleEndian.Uint16(acl)
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perm := binary.LittleEndian.Uint16(acl[2:])
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id := binary.LittleEndian.Uint32(acl[4:])
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switch tag {
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case aclTagUserObj:
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text = append(text, "user:"...)
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case aclTagUser:
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text = append(text, "user:"...)
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text = strconv.AppendUint(text, uint64(id), 10)
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case aclTagGroupObj:
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text = append(text, "group:"...)
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case aclTagGroup:
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text = append(text, "group:"...)
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text = strconv.AppendUint(text, uint64(id), 10)
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case aclTagMask:
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text = append(text, "mask:"...)
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case aclTagOther:
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text = append(text, "other:"...)
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default:
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return "", errors.New("unknown tag")
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}
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text = append(text, ':')
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text = append(text, aclPermText(perm)...)
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text = append(text, '\n')
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}
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return string(text), nil
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}
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func aclPermText(p uint16) []byte {
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s := []byte("---")
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if p&aclPermRead != 0 {
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s[0] = 'r'
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}
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if p&aclPermWrite != 0 {
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s[1] = 'w'
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}
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if p&aclPermExecute != 0 {
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s[2] = 'x'
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}
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return s
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}
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