[Bug 214885] New: random.{4,7} [man-pages 5.13] do not reflect changes to /dev/random semantics since kernel 5.6 - bugzilla-daemon

From: bugzilla-daemon@bugzilla.kernel.org
To: linux-man@vger.kernel.org
Subject: [Bug 214885] New: random.{4,7} [man-pages 5.13] do not reflect changes to /dev/random semantics since kernel 5.6
Date: Sat, 30 Oct 2021 16:42:02 +0000	[thread overview]
Message-ID: <bug-214885-11311@https.bugzilla.kernel.org/> (raw)

https://bugzilla.kernel.org/show_bug.cgi?id=214885

            Bug ID: 214885
           Summary: random.{4,7} [man-pages 5.13] do not reflect changes
                    to /dev/random semantics since kernel 5.6
           Product: Documentation
           Version: unspecified
          Hardware: All
                OS: Linux
            Status: NEW
          Severity: low
          Priority: P1
         Component: man-pages
          Assignee: documentation_man-pages@kernel-bugs.osdl.org
          Reporter: kerbug@zplane.com
        Regression: No

In kernel 5.6, the semantics of reading from /dev/random were changed
significantly [1][2]. If my understanding of [1] is correct -- and perhaps it
is not, I am not claiming any expertise -- /dev/random now behaves essentially
like /dev/urandom, except that it blocks only in the case of insufficient
initial entropy during boot, but never blocks thereafter. A few quick
experiments using kernel 5.14.14 seem to confirm that understanding.

This is a significant behavioral change but it does not seem to be reflected in
either random.4 or random.7 from man-pages release 5.13 (as provided in Arch
Linux man-pages 5.13-1). In looking thru the change history of those pages, it
does not seem that there have been any updates to either since man-pages 4.10. 

I'd be happy to offer a patch, but the required changes are not trivial and am
hestitant to contribute language on something that I don't have sufficient
familiarity with. 

Based on my quick experiments with kernel 5.14.14, at least the following
statements in random.4 seem to be entirely invalidated by the post 5.6
behavior:

  A read(2) from /dev/random will return at most 512 bytes (340
  bytes on Linux kernels before version 2.6.12):

      Observed behavior with 5.14.14: It returns up to 32MB, just as
/dev/urandom does.

  The subsection describing read_wakeup_threshold:

      This pseudo-file read_wakeup_threshold no longer exists in
/proc/sys/kernel/random.

- Glenn

[1]
https://github.com/torvalds/linux/commit/30c08efec8884fb106b8e57094baa51bb4c44e32
[2] https://lwn.net/Articles/808575/

-- 
You may reply to this email to add a comment.

You are receiving this mail because:
You are watching the assignee of the bug.