archive/zip: off-by-one writing directory64 records

[rsc]

archive/zip/writer.go says:

if records > uint16max || size > uint32max || offset > uint32max {

but each of these > should probably be >=.

See the similar bug fixed in https://go-review.googlesource.com/#/c/18317/ for writing data files of size uint32max.

[quentinmit]

records should definitely be >= since there is an additional end record. I think the size needs to account for directoryEndLen extra bytes. I don't see why offset needs to be >= however. So I propose this set of rules:

if records > uint16max-1 || size > uint32max-directoryEndLen || offset > uint32max 

ping @rsc

[rsc]

In the zip format encoding, the ^0 value means "there is a bigger value encoded next". If you encode offset 0xFFFFFFFF meaning 0xFFFFFFFF, a decoder will see it as "there's a 64-bit value coming next". If the encoding does not include that 64-bit value, the decoder will get confused. See CL 18317 for an example of this with the file data size field.

[gopherbot]

CL https://golang.org/cl/33012 mentions this issue.

[gopherbot]

CL https://golang.org/cl/33291 mentions this issue.