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keywords: switch 'xattr' to base64

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Rather than an arbitrary election of hashing the xattr value with SHA1
to avoid leaking the value. By going with base64 encoding it allows for
the possibility of restoring a directory with the values stored in the
manifest.

Signed-off-by: Vincent Batts <vbatts@hashbangbash.com>
This commit is contained in:
Vincent Batts 2016-07-27 17:40:51 -04:00
parent 27459241ae
commit 7e2ed0b70b
2 changed files with 10 additions and 12 deletions
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16
README.md
View file

@ -55,9 +55,9 @@ keyword and values are established in the `/set` command.
```mtree
# .
/set type=file nlink=1 mode=0664 uid=1000 gid=1000
. size=4096 type=dir mode=0775 nlink=6 time=1459370191.11179595 xattr.security.selinux=6b53fb56e2e61a6c6d672817791db03ebe693748
LICENSE size=1502 time=1458851690.583562292 xattr.security.selinux=6b53fb56e2e61a6c6d672817791db03ebe693748
README.md size=2366 mode=0644 time=1459369604.0 xattr.security.selinux=6b53fb56e2e61a6c6d672817791db03ebe693748
. size=4096 type=dir mode=0775 nlink=6 time=1459370191.11179595 xattr.security.selinux=dW5jb25maW5lZF91Om9iamVjdF9yOnVzZXJfaG9tZV90OnMwAA==
LICENSE size=1502 time=1458851690.583562292 xattr.security.selinux=dW5jb25maW5lZF91Om9iamVjdF9yOnVzZXJfaG9tZV90OnMwAA==
README.md size=2366 mode=0644 time=1459369604.0 xattr.security.selinux=dW5jb25maW5lZF91Om9iamVjdF9yOnVzZXJfaG9tZV90OnMwAA==
[...]
```
@ -69,11 +69,9 @@ attributes as well as FreeBSD extended attributes.
Since extended attributes are an unordered hashmap, this approach allows for
checking each `<namespace>.<key>` individually.
The value is the [SHA1 digest][sha1] of the value of the particular extended
attribute. Since the values themselves could be raw bytes, this approach both
avoids issues with encoding, as well as issues of information leaking. The
designation of SHA1 is arbitrary and seen as a general "good enough" assertion
of the value.
The value is the [base64 encoded][base64] of the value of the particular
extended attribute. Since the values themselves could be raw bytes, this
approach avoids issues with encoding.
### Tar form
@ -195,5 +193,5 @@ go build .
[libarchive-formats(5)]: https://www.freebsd.org/cgi/man.cgi?query=libarchive-formats&sektion=5&n=1
[archiecobbs/mtree-port]: https://github.com/archiecobbs/mtree-port
[godoc]: https://godoc.org/github.com/vbatts/go-mtree
[sha1]: https://tools.ietf.org/html/rfc3174
[tar]: http://man7.org/linux/man-pages/man1/tar.1.html
[base64]: https://tools.ietf.org/html/rfc4648

6
keywords_linux.go
View file

@ -2,7 +2,7 @@ package mtree
import (
"archive/tar"
"crypto/sha1"
"encoding/base64"
"fmt"
"io"
"os"
@ -55,7 +55,7 @@ var (
}
klist := []string{}
for k, v := range hdr.Xattrs {
klist = append(klist, fmt.Sprintf("xattr.%s=%x", k, sha1.Sum([]byte(v))))
klist = append(klist, fmt.Sprintf("xattr.%s=%s", k, base64.StdEncoding.EncodeToString([]byte(v))))
}
return strings.Join(klist, " "), nil
}
@ -70,7 +70,7 @@ var (
if err != nil {
return "", err
}
klist[i] = fmt.Sprintf("xattr.%s=%x", xlist[i], sha1.Sum(data))
klist[i] = fmt.Sprintf("xattr.%s=%s", xlist[i], base64.StdEncoding.EncodeToString(data))
}
return strings.Join(klist, " "), nil
}