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Post-Boot Delays in SSH Access Due to Small Entropy Pool

posted by Fnord666 on Friday December 21 2018, @06:19PM   Printer-friendly
from the chaos-monkey dept.

canopic jug writes:

Recent upgrades that depend on the new Linux getrandom() syscall can cause OpenSSH to delay starting for tens of minutes while waiting for enough bytes of randomness. There are currently not any feasible work-arounds.

Systemd makes this behaviour worse, see issue #4271, #4513 and #10621.
Basically as of now the entropy file saved as /var/lib/systemd/random-seed will not - drumroll - add entropy to the random pool when played back during boot. Actually it will. It will just not be accounted for. So Linux doesn't know. And continues blocking getrandom(). This is obviously different from SysVinit times when /var/lib/urandom/random-seed (that you still have laying around on updated systems) made sure the system carried enough entropy over reboot to continue working right after enough of the system was booted.

#4167 is a re-opened discussion about systemd eating randomness early at boot (hashmaps in PID 0...). Some Debian folks participate in the recent discussion and it is worth reading if you want to learn about the mess that booting a Linux system has become.

While we're talking systemd ... #10676 also means systems will use RDRAND in the future despite Ted Ts'o's warning on RDRAND [Archive.org mirror and mirrored locally as 130905_Ted_Tso_on_RDRAND.pdf, 205kB as Google+ will be discontinued in April 2019].

Related post: OneRNG: a Fully-Open Entropy Generator (2014)

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  • (Score: 0) by Anonymous Coward on Friday December 21 2018, @09:07PM

    by Anonymous Coward on Friday December 21 2018, @09:07PM (#777316)

    Proved he didn't know shit.

    The complaint about the driver with the default enable option? They have been doing that since 3.0 or 2.6 something, at least. Plus nobody has been bothering with arch-specific filters, even on things like ARM-specific FPGA glue, causing SPARC, Alpha, S390, and even i686 arches to have loads of crap that are irrelevant to them, as well as dozens to hundreds of default-enabled drivers.

    As stated in PP, the linux kernel has been on the road to a not so well polished turd for a while. I personally peg it at 2.6.9 when they broke API compatibility without using a new kernel major or minor version, instead breaking it twice more in the .1x and .2x series (I don't remember the specific versions, maybe someone with historical digging skills can figure it out.)

    Point being, Linux has lost its way. The downside being nothing else once had the broad compatibility driver and protocol-wise, and now even Linux is taking that away.