This is a note to let you know that I've just added the patch titled random: always wake up entropy writers after extraction to the 5.17-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: random-always-wake-up-entropy-writers-after-extraction.patch and it can be found in the queue-5.17 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From foo@baz Thu May 26 04:19:10 PM CEST 2022 From: "Jason A. Donenfeld" <Jason@xxxxxxxxx> Date: Sat, 5 Feb 2022 14:00:58 +0100 Subject: random: always wake up entropy writers after extraction From: "Jason A. Donenfeld" <Jason@xxxxxxxxx> commit 489c7fc44b5740d377e8cfdbf0851036e493af00 upstream. Now that POOL_BITS == POOL_MIN_BITS, we must unconditionally wake up entropy writers after every extraction. Therefore there's no point of write_wakeup_threshold, so we can move it to the dustbin of unused compatibility sysctls. While we're at it, we can fix a small comparison where we were waking up after <= min rather than < min. Cc: Theodore Ts'o <tytso@xxxxxxx> Suggested-by: Eric Biggers <ebiggers@xxxxxxxxxx> Reviewed-by: Eric Biggers <ebiggers@xxxxxxxxxx> Reviewed-by: Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- Documentation/admin-guide/sysctl/kernel.rst | 7 ++++- drivers/char/random.c | 33 +++++++++------------------- 2 files changed, 16 insertions(+), 24 deletions(-) --- a/Documentation/admin-guide/sysctl/kernel.rst +++ b/Documentation/admin-guide/sysctl/kernel.rst @@ -1030,14 +1030,17 @@ This is a directory, with the following * ``poolsize``: the entropy pool size, in bits; * ``urandom_min_reseed_secs``: obsolete (used to determine the minimum - number of seconds between urandom pool reseeding). + number of seconds between urandom pool reseeding). This file is + writable for compatibility purposes, but writing to it has no effect + on any RNG behavior. * ``uuid``: a UUID generated every time this is retrieved (this can thus be used to generate UUIDs at will); * ``write_wakeup_threshold``: when the entropy count drops below this (as a number of bits), processes waiting to write to ``/dev/random`` - are woken up. + are woken up. This file is writable for compatibility purposes, but + writing to it has no effect on any RNG behavior. If ``drivers/char/random.c`` is built with ``ADD_INTERRUPT_BENCH`` defined, these additional entries are present: --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -296,12 +296,6 @@ enum { */ static DECLARE_WAIT_QUEUE_HEAD(random_write_wait); static struct fasync_struct *fasync; -/* - * If the entropy count falls under this number of bits, then we - * should wake up processes which are selecting or polling on write - * access to /dev/random. - */ -static int random_write_wakeup_bits = POOL_MIN_BITS; static DEFINE_SPINLOCK(random_ready_list_lock); static LIST_HEAD(random_ready_list); @@ -739,10 +733,8 @@ static void crng_reseed(struct crng_stat return; } while (cmpxchg(&input_pool.entropy_count, entropy_count, 0) != entropy_count); extract_entropy(buf.key, sizeof(buf.key)); - if (random_write_wakeup_bits) { - wake_up_interruptible(&random_write_wait); - kill_fasync(&fasync, SIGIO, POLL_OUT); - } + wake_up_interruptible(&random_write_wait); + kill_fasync(&fasync, SIGIO, POLL_OUT); } else { _extract_crng(&primary_crng, buf.block); _crng_backtrack_protect(&primary_crng, buf.block, @@ -1471,7 +1463,7 @@ static __poll_t random_poll(struct file mask = 0; if (crng_ready()) mask |= EPOLLIN | EPOLLRDNORM; - if (input_pool.entropy_count < random_write_wakeup_bits) + if (input_pool.entropy_count < POOL_MIN_BITS) mask |= EPOLLOUT | EPOLLWRNORM; return mask; } @@ -1556,7 +1548,7 @@ static long random_ioctl(struct file *f, */ if (!capable(CAP_SYS_ADMIN)) return -EPERM; - if (xchg(&input_pool.entropy_count, 0) && random_write_wakeup_bits) { + if (xchg(&input_pool.entropy_count, 0)) { wake_up_interruptible(&random_write_wait); kill_fasync(&fasync, SIGIO, POLL_OUT); } @@ -1636,9 +1628,9 @@ SYSCALL_DEFINE3(getrandom, char __user * #include <linux/sysctl.h> -static int min_write_thresh; -static int max_write_thresh = POOL_BITS; static int random_min_urandom_seed = 60; +static int random_write_wakeup_bits = POOL_MIN_BITS; +static int sysctl_poolsize = POOL_BITS; static char sysctl_bootid[16]; /* @@ -1677,7 +1669,6 @@ static int proc_do_uuid(struct ctl_table return proc_dostring(&fake_table, write, buffer, lenp, ppos); } -static int sysctl_poolsize = POOL_BITS; static struct ctl_table random_table[] = { { .procname = "poolsize", @@ -1698,9 +1689,7 @@ static struct ctl_table random_table[] = .data = &random_write_wakeup_bits, .maxlen = sizeof(int), .mode = 0644, - .proc_handler = proc_dointvec_minmax, - .extra1 = &min_write_thresh, - .extra2 = &max_write_thresh, + .proc_handler = proc_dointvec, }, { .procname = "urandom_min_reseed_secs", @@ -1892,13 +1881,13 @@ void add_hwgenerator_randomness(const ch } /* Throttle writing if we're above the trickle threshold. - * We'll be woken up again once below random_write_wakeup_thresh, - * when the calling thread is about to terminate, or once - * CRNG_RESEED_INTERVAL has lapsed. + * We'll be woken up again once below POOL_MIN_BITS, when + * the calling thread is about to terminate, or once + * CRNG_RESEED_INTERVAL has elapsed. */ wait_event_interruptible_timeout(random_write_wait, !system_wq || kthread_should_stop() || - input_pool.entropy_count <= random_write_wakeup_bits, + input_pool.entropy_count < POOL_MIN_BITS, CRNG_RESEED_INTERVAL); mix_pool_bytes(buffer, count); credit_entropy_bits(entropy); Patches currently in stable-queue which might be from Jason@xxxxxxxxx are queue-5.17/random-remove-ratelimiting-for-in-kernel-unseeded-randomness.patch queue-5.17/random-introduce-drain_entropy-helper-to-declutter-crng_reseed.patch queue-5.17/random-fix-sysctl-documentation-nits.patch queue-5.17/random-help-compiler-out-with-fast_mix-by-using-simpler-arguments.patch queue-5.17/random-use-simpler-fast-key-erasure-flow-on-per-cpu-keys.patch queue-5.17/siphash-use-one-source-of-truth-for-siphash-permutations.patch queue-5.17/um-use-fallback-for-random_get_entropy-instead-of-zero.patch queue-5.17/random-get-rid-of-secondary-crngs.patch queue-5.17/random-check-for-crng_init-0-in-add_device_randomness.patch queue-5.17/random-order-timer-entropy-functions-below-interrupt-functions.patch queue-5.17/random-unify-batched-entropy-implementations.patch queue-5.17/random-remove-unused-tracepoints.patch queue-5.17/random-add-proper-spdx-header.patch queue-5.17/random-group-entropy-collection-functions.patch queue-5.17/random-don-t-let-644-read-only-sysctls-be-written-to.patch queue-5.17/random-make-consistent-use-of-buf-and-len.patch queue-5.17/random-make-consistent-usage-of-crng_ready.patch queue-5.17/random-make-random_get_entropy-return-an-unsigned-long.patch queue-5.17/random-move-randomize_page-into-mm-where-it-belongs.patch queue-5.17/random-use-first-128-bits-of-input-as-fast-init.patch queue-5.17/random-use-computational-hash-for-entropy-extraction.patch queue-5.17/random-unify-cycles_t-and-jiffies-usage-and-types.patch queue-5.17/random-rewrite-header-introductory-comment.patch queue-5.17/random-use-proper-return-types-on-get_random_-int-long-_wait.patch queue-5.17/random-check-for-signal-and-try-earlier-when-generating-entropy.patch queue-5.17/s390-define-get_cycles-macro-for-arch-override.patch queue-5.17/random-ensure-early-rdseed-goes-through-mixer-on-init.patch queue-5.17/random-cleanup-uuid-handling.patch queue-5.17/random-mix-build-time-latent-entropy-into-pool-at-init.patch queue-5.17/random-reseed-more-often-immediately-after-booting.patch queue-5.17/random-remove-ifdef-d-out-interrupt-bench.patch queue-5.17/timekeeping-add-raw-clock-fallback-for-random_get_entropy.patch queue-5.17/random-allow-partial-reads-if-later-user-copies-fail.patch queue-5.17/random.patch queue-5.17/random-use-static-branch-for-crng_ready.patch queue-5.17/arm-use-fallback-for-random_get_entropy-instead-of-zero.patch queue-5.17/random-tie-batched-entropy-generation-to-base_crng-generation.patch queue-5.17/random-round-robin-registers-as-ulong-not-u32.patch queue-5.17/mips-use-fallback-for-random_get_entropy-instead-of-just-c0-random.patch queue-5.17/random-do-not-take-pool-spinlock-at-boot.patch queue-5.17/random-absorb-fast-pool-into-input-pool-after-fast-load.patch queue-5.17/random-remove-useless-header-comment.patch queue-5.17/random-do-not-allow-user-to-keep-crng-key-around-on-stack.patch queue-5.17/random-avoid-initializing-twice-in-credit-race.patch queue-5.17/random-move-initialization-functions-out-of-hot-pages.patch queue-5.17/random-do-not-pretend-to-handle-premature-next-security-model.patch queue-5.17/random-remove-batched-entropy-locking.patch queue-5.17/random-do-not-use-batches-when-crng_ready.patch queue-5.17/random-deobfuscate-irq-u32-u64-contributions.patch queue-5.17/random-group-crng-functions.patch queue-5.17/random-defer-fast-pool-mixing-to-worker.patch queue-5.17/random-group-initialization-wait-functions.patch queue-5.17/random-treat-bootloader-trust-toggle-the-same-way-as-cpu-trust-toggle.patch queue-5.17/random-do-crng-pre-init-loading-in-worker-rather-than-irq.patch queue-5.17/random-give-sysctl_random_min_urandom_seed-a-more-sensible-value.patch queue-5.17/random-re-add-removed-comment-about-get_random_-u32-u64-reseeding.patch queue-5.17/m68k-use-fallback-for-random_get_entropy-instead-of-zero.patch queue-5.17/random-clear-fast-pool-crng-and-batches-in-cpuhp-bring-up.patch queue-5.17/random-move-initialization-out-of-reseeding-hot-path.patch queue-5.17/x86-tsc-use-fallback-for-random_get_entropy-instead-of-zero.patch queue-5.17/random-use-rdseed-instead-of-rdrand-in-entropy-extraction.patch queue-5.17/random-remove-use_input_pool-parameter-from-crng_reseed.patch queue-5.17/random-use-siphash-as-interrupt-entropy-accumulator.patch queue-5.17/random-skip-fast_init-if-hwrng-provides-large-chunk-of-entropy.patch queue-5.17/random-fix-locking-for-crng_init-in-crng_reseed.patch queue-5.17/random-group-entropy-extraction-functions.patch queue-5.17/random-group-userspace-read-write-functions.patch queue-5.17/random-credit-architectural-init-the-exact-amount.patch queue-5.17/random-remove-outdated-int_max-6-check-in-urandom_read.patch queue-5.17/random-use-hash-function-for-crng_slow_load.patch queue-5.17/random-inline-leaves-of-rand_initialize.patch queue-5.17/random-check-for-signals-after-page-of-pool-writes.patch queue-5.17/random-simplify-entropy-debiting.patch queue-5.17/random-remove-extern-from-functions-in-header.patch queue-5.17/random-check-for-signal_pending-outside-of-need_resched-check.patch queue-5.17/random-do-not-use-input-pool-from-hard-irqs.patch queue-5.17/random-wire-up-fops-splice_-read-write-_iter.patch queue-5.17/random-fix-locking-in-crng_fast_load.patch queue-5.17/random-make-more-consistent-use-of-integer-types.patch queue-5.17/random-insist-on-random_get_entropy-existing-in-order-to-simplify.patch queue-5.17/powerpc-define-get_cycles-macro-for-arch-override.patch queue-5.17/parisc-define-get_cycles-macro-for-arch-override.patch queue-5.17/sparc-use-fallback-for-random_get_entropy-instead-of-zero.patch queue-5.17/random-group-sysctl-functions.patch queue-5.17/nios2-use-fallback-for-random_get_entropy-instead-of-zero.patch queue-5.17/init-call-time_init-before-rand_initialize.patch queue-5.17/riscv-use-fallback-for-random_get_entropy-instead-of-zero.patch queue-5.17/random-replace-custom-notifier-chain-with-standard-one.patch queue-5.17/random-always-wake-up-entropy-writers-after-extraction.patch queue-5.17/random-pull-add_hwgenerator_randomness-declaration-into-random.h.patch queue-5.17/ia64-define-get_cycles-macro-for-arch-override.patch queue-5.17/random-handle-latent-entropy-and-command-line-from-random_init.patch queue-5.17/random-make-credit_entropy_bits-always-safe.patch queue-5.17/random-use-proper-jiffies-comparison-macro.patch queue-5.17/random-zero-buffer-after-reading-entropy-from-userspace.patch queue-5.17/random-do-not-xor-rdrand-when-writing-into-dev-random.patch queue-5.17/random-use-linear-min-entropy-accumulation-crediting.patch queue-5.17/random-unify-early-init-crng-load-accounting.patch queue-5.17/alpha-define-get_cycles-macro-for-arch-override.patch queue-5.17/random-convert-to-using-fops-read_iter.patch queue-5.17/xtensa-use-fallback-for-random_get_entropy-instead-of-zero.patch queue-5.17/random-use-symbolic-constants-for-crng_init-states.patch queue-5.17/random-convert-to-using-fops-write_iter.patch queue-5.17/random-only-wake-up-writers-after-zap-if-threshold-was-passed.patch queue-5.17/random-document-crng_fast_key_erasure-destination-possibility.patch queue-5.17/random-remove-whitespace-and-reorder-includes.patch queue-5.17/random-do-not-split-fast-init-input-in-add_hwgenerator_randomness.patch