https://bz.apache.org/bugzilla/show_bug.cgi?id=65984
Bug ID: 65984
Summary: `fcgi_check_authn` (or rather `handle_response`)
appears to be not robust to flush on socket
Product: Apache httpd-2
Version: 2.4.41
Hardware: All
OS: All
Status: NEW
Severity: normal
Priority: P2
Component: mod_authnz_fcgi
Assignee: [email protected]
Reporter: [email protected]
Target Milestone: ---
Created attachment 38237
--> https://bz.apache.org/bugzilla/attachment.cgi?id=38237&action=edit
try this script with the flush lines commented vs uncommented
I am in the process of writing an authentication module[1] that avails itself
of mod_authnz_fcgi[2] to complement the necessary behaviour. The FastCGI
authenticator[3] is expected to send content (e.g. 401 error pages) when
authentication fails. This currently does not happen. What happens instead is
the default Apache error page is displayed[4] and the body content coming from
the authenticator is discarded.
In order to diagnose this situation, I created two separate, stripped-down
FastCGI scripts that only return a 401 with a body message, one in Ruby and one
in Perl. Both functioned as expected. Upon looking at the
Rack::Handler::FastCGI source I noticed that it flushes its output after the
headers and again after each body chunk, and changed the stripped-down scripts
to mimic it. This change yielded the same body-discarding behaviour as the Rack
version.
What appears to be happening, then, is mod_authnz_fcgi is abandoning its socket
to the FastCGI authenticator after the latter flushes the socket.
Footnotes:
1) Using Ruby and Rack (https://github.com/doriantaylor/rb-lazyauth), though in
principle this detail doesn't matter.
2) Note that the Apache version selected for this report is the one where this
behaviour was observed (i.e., that ships with Ubuntu 20.04 LTS).
3)
https://httpd.apache.org/docs/2.4/mod/mod_authnz_fcgi.html#authnzfcgicheckauthnprovider
4) The error pages' Content-Type header overrides whatever comes out of the
FCGI authenticator no matter what, but that is probably a separate issue.
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