Streamed multipart UploadPart called Reserve(contentLength) before reading any
body bytes, so the pool immediately allocated one 1 MiB page per MiB of the
client-declared Content-Length (or X-Amz-Decoded-Content-Length). An client
could declare a huge part size, send no body, and force an arbitrarily large
allocation without paying the bandwidth cost of the declared body.
Drop the Reserve so the pool-backed buffer grows a page at a time as the body
is actually read: memory now tracks the bytes received, not the unverified
header.
Nick Craig-Wood
efc8adb0e5