From: DJ Delorie <dj@redhat.com>
To: libc-alpha@sourceware.org
Subject: RFC: system-wide default tunables
Date: Wed, 04 Oct 2023 16:55:18 -0400 [thread overview]
Message-ID: <xn1qeayuo9.fsf@greed.delorie.com> (raw)
Before I start on actual coding, I'm sharing my thoughts on this
project to gain consensus...
Problem: tunables are set by an environment variable, and may be
limited by security settings, containerization, etc. Plus users may
not assume that the env var is pre-set, and just overwrite it.
Solution: Add a way to specify system-wide defaults for tunables.
Ideas:
* Specify some file or files in /etc that contain tunables settings.
Follow the ld.so.conf patterns, allow subdirectories, etc.
* Store tunables info in /etc/ld.so.cache in a new slot at the end,
with a new enum for the chunk. This way older glibc will just
ignore it. Parsing and storing will be done via ldconfig.
* Values in ld.so.cache will be parsed but not range checked; that's
dependent on what the glibc app expects.
* read those, do range checking, and call callbacks at runtime
* To speed processing, encode a hash for each tunable name, both in
glibc's table (which is built at glibc build time) and in
/etc/ld.so.cache. Comparing the hash typically fails but avoids a
string compare. Matching hashes are followed by a string compare to
verify. The hash need not be crypographically secure.
* I'm not going to try to add some "syntax" to specify if a tunable is
overridable or not; this is a simple default-only change.
* Tunables set by these defaults will not be disabled for setuid
programs; it's assumed they're a "trusted source".
next reply other threads:[~2023-10-04 20:55 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-04 20:55 DJ Delorie [this message]
2023-10-06 14:44 ` Adhemerval Zanella Netto
2023-10-06 17:12 ` Adhemerval Zanella Netto
2023-10-06 18:29 ` DJ Delorie
2023-10-06 19:14 ` Adhemerval Zanella Netto
2023-10-06 20:25 ` DJ Delorie
2023-10-17 14:10 ` Adhemerval Zanella Netto
2023-10-17 14:17 ` Siddhesh Poyarekar
2023-10-17 14:37 ` Siddhesh Poyarekar
2023-10-17 15:43 ` DJ Delorie
2023-10-17 15:58 ` Siddhesh Poyarekar
2023-10-17 16:45 ` DJ Delorie
2023-10-17 16:55 ` Siddhesh Poyarekar
2023-10-17 17:14 ` DJ Delorie
2023-10-18 14:20 ` Siddhesh Poyarekar
2023-10-17 17:40 ` Zack Weinberg
2023-10-17 17:47 ` DJ Delorie
2023-10-17 18:17 ` Zack Weinberg
2023-10-17 18:21 ` DJ Delorie
2023-10-06 22:04 ` DJ Delorie
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=xn1qeayuo9.fsf@greed.delorie.com \
--to=dj@redhat.com \
--cc=libc-alpha@sourceware.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).