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archive/tar: use placeholder name for global PAX records

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Several usages of tar (reasonably) just use the Header.FileInfo
to determine the type of the header. However, the os.FileMode type
is not expressive enough to represent "files" that are not files
at all, but some form of metadata.

Thus, Header{Typeflag: TypeXGlobalHeader}.FileInfo().Mode().IsRegular()
reports true, even though the expected result may have been false.

To reduce (not eliminate) the possibility of failure for such usages,
use the placeholder filename from the global PAX headers.
Thus, in the event the user did not handle special "meta" headers
specifically, they will just be written to disk as a regular file.

As an example use case, the "git archive --format=tgz" command produces
an archive where the first "file" is a global PAX header with the
name "global_pax_header". For users that do not explicitly check
the Header.Typeflag field to ignore such headers, they may end up
extracting a file named "global_pax_header". While it is a bogus file,
it at least does not stop the extraction process.

Updates #22748

Change-Id: I28448b528dcfacb4e92311824c33c71b482f49c9
Reviewed-on: https://go-review.googlesource.com/78355
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
This commit is contained in:
Joe Tsai 2017-11-16 10:15:34 -08:00 committed by Joe Tsai
parent ba1943cd23
commit 9ec0c7abe1
4 changed files with 10 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
src/archive/tar/common.go
View File

@ -438,8 +438,9 @@ func (h Header) allowedFormats() (format Format, paxHdrs map[string]string, err
case TypeXHeader, TypeGNULongName, TypeGNULongLink:
return FormatUnknown, nil, headerError{"cannot manually encode TypeXHeader, TypeGNULongName, or TypeGNULongLink headers"}
case TypeXGlobalHeader:
if !reflect.DeepEqual(h, Header{Typeflag: h.Typeflag, Xattrs: h.Xattrs, PAXRecords: h.PAXRecords, Format: h.Format}) {
return FormatUnknown, nil, headerError{"only PAXRecords may be set for TypeXGlobalHeader"}
h2 := Header{Name: h.Name, Typeflag: h.Typeflag, Xattrs: h.Xattrs, PAXRecords: h.PAXRecords, Format: h.Format}
if !reflect.DeepEqual(h, h2) {
return FormatUnknown, nil, headerError{"only PAXRecords should be set for TypeXGlobalHeader"}
}
whyOnlyPAX = "only PAX supports TypeXGlobalHeader"
format.mayOnlyBe(FormatPAX)

1
src/archive/tar/reader.go
View File

@ -95,6 +95,7 @@ loop:
if hdr.Typeflag == TypeXGlobalHeader {
mergePAX(hdr, paxHdrs)
return &Header{
Name: hdr.Name,
Typeflag: hdr.Typeflag,
Xattrs: hdr.Xattrs,
PAXRecords: hdr.PAXRecords,

2
src/archive/tar/reader_test.go
View File

@ -285,6 +285,7 @@ func TestReader(t *testing.T) {
file: "testdata/pax-global-records.tar",
headers: []*Header{{
Typeflag: TypeXGlobalHeader,
Name: "global1",
PAXRecords: map[string]string{"path": "global1", "mtime": "1500000000.0"},
Format: FormatPAX,
}, {
@ -300,6 +301,7 @@ func TestReader(t *testing.T) {
Format: FormatPAX,
}, {
Typeflag: TypeXGlobalHeader,
Name: "GlobalHead.0.0",
PAXRecords: map[string]string{"path": ""},
Format: FormatPAX,
}, {

5
src/archive/tar/writer.go
View File

@ -179,7 +179,10 @@ func (tw *Writer) writePAXHeader(hdr *Header, paxHdrs map[string]string) error {
var name string
var flag byte
if isGlobal {
name = "GlobalHead.0.0"
name = realName
if name == "" {
name = "GlobalHead.0.0"
}
flag = TypeXGlobalHeader
} else {
dir, file := path.Split(realName)