Re: [PATCH v1] random: block in /dev/urandom

Guenter Roeck
2022-03-22T16:00:26Z

On Thu, Feb 17, 2022 at 05:28:48PM +0100, Jason A. Donenfeld wrote:
> This topic has come up countless times, and usually doesn't go anywhere.
> This time I thought I'd bring it up with a slightly narrower focus,
> updated for some developments over the last three years: we finally can
> make /dev/urandom always secure, in light of the fact that our RNG is
> now always seeded.
>

[ ... ]

This patch (or a later version of it) made it into mainline and causes a
large number of qemu boot test failures for various architectures (arm,
m68k, microblaze, sparc32, xtensa are the ones I observed). Common
denominator is that boot hangs at "Saving random seed:". A sample bisect
log is attached. Reverting this patch fixes the problem.

Guenter

---
# bad: [8565d64430f8278bea38dab0a3ab60b4e11c71e4] Merge tag 'bounds-fixes-v5.18-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux
# good: [f443e374ae131c168a065ea1748feac6b2e76613] Linux 5.17
git bisect start 'HEAD' 'v5.17'
# bad: [5628b8de1228436d47491c662dc521bc138a3d43] Merge tag 'random-5.18-rc1-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/crng/random
git bisect bad 5628b8de1228436d47491c662dc521bc138a3d43
# good: [a04b1bf574e1f4875ea91f5c62ca051666443200] Merge tag 'for-5.18/parisc-1' of git://git.kernel.org/pub/scm/linux/kernel/git/deller/parisc-linux
git bisect good a04b1bf574e1f4875ea91f5c62ca051666443200
# good: [242ba6656d604aa8dc87451fc08143cb28d5a587] Merge tag 'acpi-5.18-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm
git bisect good 242ba6656d604aa8dc87451fc08143cb28d5a587
# good: [02b82b02c34321dde10d003aafcd831a769b2a8a] Merge tag 'pm-5.18-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm
git bisect good 02b82b02c34321dde10d003aafcd831a769b2a8a
# bad: [77553cf8f44863b31da242cf24671d76ddb61597] random: don't let 644 read-only sysctls be written to
git bisect bad 77553cf8f44863b31da242cf24671d76ddb61597
# good: [a07fdae346c35c6ba286af1c88e0effcfa330bf9] random: add proper SPDX header
git bisect good a07fdae346c35c6ba286af1c88e0effcfa330bf9
# good: [58340f8e952b613e0ead0bed58b97b05bf4743c5] random: defer fast pool mixing to worker
git bisect good 58340f8e952b613e0ead0bed58b97b05bf4743c5
# good: [da3951ebdcd1cb1d5c750e08cd05aee7b0c04d9a] random: round-robin registers as ulong, not u32
git bisect good da3951ebdcd1cb1d5c750e08cd05aee7b0c04d9a
# good: [abded93ec1e9692920fe309f07f40bd1035f2940] random: unify cycles_t and jiffies usage and types
git bisect good abded93ec1e9692920fe309f07f40bd1035f2940
# bad: [6f98a4bfee72c22f50aedb39fb761567969865fe] random: block in /dev/urandom
git bisect bad 6f98a4bfee72c22f50aedb39fb761567969865fe
# good: [c2a7de4feb6e09f23af7accc0f882a8fa92e7ae5] random: do crng pre-init loading in worker rather than irq
git bisect good c2a7de4feb6e09f23af7accc0f882a8fa92e7ae5
# first bad commit: [6f98a4bfee72c22f50aedb39fb761567969865fe] random: block in /dev/urandom