…llocations in ReadForm

When copying form data to disk with io.Copy,
allocate only one copy buffer and reuse it rather than
creating two buffers per file (one from io.multiReader.WriteTo,
and a second one from os.File.ReadFrom).

Thanks to Jakob Ackermann (@das7pad) for reporting this issue.

For CVE-2023-24536
For #59153
For #59269

Reviewed-on: https://team-review.git.corp.google.com/c/golang/go-private/+/1802453
Run-TryBot: Damien Neil <dneil@google.com>
Reviewed-by: Julie Qiu <julieqiu@google.com>
Reviewed-by: Roland Shoemaker <bracewell@google.com>
Reviewed-on: https://team-review.git.corp.google.com/c/golang/go-private/+/1802395
Run-TryBot: Roland Shoemaker <bracewell@google.com>
Reviewed-by: Damien Neil <dneil@google.com>
Change-Id: Ie405470c92abffed3356913b37d813e982c96c8b
Reviewed-on: https://go-review.googlesource.com/c/go/+/481983
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

…ting of non-file data

For requests containing large numbers of small parts,
memory consumption of a parsed form could be about 250%
over the estimated size.

When considering the size of parsed forms, account for the size of
FileHeader structs and increase the estimate of memory consumed by
map entries.

Thanks to Jakob Ackermann (@das7pad) for reporting this issue.

For CVE-2023-24536
For #59153
For #59269

Reviewed-on: https://team-review.git.corp.google.com/c/golang/go-private/+/1802454
Run-TryBot: Damien Neil <dneil@google.com>
Reviewed-by: Roland Shoemaker <bracewell@google.com>
Reviewed-by: Julie Qiu <julieqiu@google.com>
Reviewed-on: https://team-review.git.corp.google.com/c/golang/go-private/+/1802396
Run-TryBot: Roland Shoemaker <bracewell@google.com>
Reviewed-by: Damien Neil <dneil@google.com>
Change-Id: I31bc50e9346b4eee6fbe51a18c3c57230cc066db
Reviewed-on: https://go-review.googlesource.com/c/go/+/481984
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Michael Knyszek <mknyszek@google.com>

The parsed forms of MIME headers and multipart forms can consume
substantially more memory than the size of the input data.
A malicious input containing a very large number of headers or
form parts can cause excessively large memory allocations.

Set limits on the size of MIME data:

Reader.NextPart and Reader.NextRawPart limit the the number
of headers in a part to 10000.

Reader.ReadForm limits the total number of headers in all
FileHeaders to 10000.

Both of these limits may be set with with
GODEBUG=multipartmaxheaders=<values>.

Reader.ReadForm limits the number of parts in a form to 1000.
This limit may be set with GODEBUG=multipartmaxparts=<value>.

Thanks for Jakob Ackermann (@das7pad) for reporting this issue.

For CVE-2023-24536
For #59153
For #59269

Reviewed-on: https://team-review.git.corp.google.com/c/golang/go-private/+/1802455
Run-TryBot: Damien Neil <dneil@google.com>
Reviewed-by: Roland Shoemaker <bracewell@google.com>
Reviewed-by: Julie Qiu <julieqiu@google.com>
Reviewed-on: https://team-review.git.corp.google.com/c/golang/go-private/+/1801087
Reviewed-by: Damien Neil <dneil@google.com>
Run-TryBot: Roland Shoemaker <bracewell@google.com>
Change-Id: If134890d75f0d95c681d67234daf191ba08e6424
Reviewed-on: https://go-review.googlesource.com/c/go/+/481985
Run-TryBot: Michael Knyszek <mknyszek@google.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

…DEBUG settings

This change documents the new GODEBUG settings introduced for
html/template and mime/multipart, released with Go 1.19.8 and Go 1.20.3
as part of a security fix.

Updates #59153.
For #59269.
Updates #59234.
For #59271.

Change-Id: I25f4d8245da3301dccccfb44da8ff1a5985392a4
Reviewed-on: https://go-review.googlesource.com/c/go/+/482535
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Damien Neil <dneil@google.com>
Run-TryBot: Michael Knyszek <mknyszek@google.com>