Backport #38044 by @metsw24-max
**Packages-index stanza injection via Debian control file**
A `.deb` whose `control` file appends extra paragraphs after a blank
line was still accepted, and `ParseControlFile` stored the whole
multi-stanza blob in `p.Control`. That blob is re-emitted verbatim into
the generated `Packages` index, so the embedded blank line splits it
into separate stanzas and an uploader can smuggle a package entry with
an attacker-chosen `Filename` into the shared index. A binary control
file only holds one stanza, so parsing now stops at the blank line that
terminates it; well-formed packages are unaffected and the new subtest
covers the trailing-stanza case.
Signed-off-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: metsw24-max <metsw24@gmail.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: bircni <bircni@icloud.com>
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