This is a note to let you know that I've just added the patch titled
random: check for signals every PAGE_SIZE chunk of /dev/[u]random
to the 4.19-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-check-for-signals-every-page_size-chunk-of-dev-random.patch
and it can be found in the queue-4.19 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 Fri Jun 17 08:58:56 AM CEST 2022
From: "Jason A. Donenfeld" <Jason@xxxxxxxxx>
Date: Wed, 6 Apr 2022 02:36:16 +0200
Subject: random: check for signals every PAGE_SIZE chunk of /dev/[u]random
From: "Jason A. Donenfeld" <Jason@xxxxxxxxx>
commit e3c1c4fd9e6d14059ed93ebfe15e1c57793b1a05 upstream.
In 1448769c9cdb ("random: check for signal_pending() outside of
need_resched() check"), Jann pointed out that we previously were only
checking the TIF_NOTIFY_SIGNAL and TIF_SIGPENDING flags if the process
had TIF_NEED_RESCHED set, which meant in practice, super long reads to
/dev/[u]random would delay signal handling by a long time. I tried this
using the below program, and indeed I wasn't able to interrupt a
/dev/urandom read until after several megabytes had been read. The bug
he fixed has always been there, and so code that reads from /dev/urandom
without checking the return value of read() has mostly worked for a long
time, for most sizes, not just for <= 256.
Maybe it makes sense to keep that code working. The reason it was so
small prior, ignoring the fact that it didn't work anyway, was likely
because /dev/random used to block, and that could happen for pretty
large lengths of time while entropy was gathered. But now, it's just a
chacha20 call, which is extremely fast and is just operating on pure
data, without having to wait for some external event. In that sense,
/dev/[u]random is a lot more like /dev/zero.
Taking a page out of /dev/zero's read_zero() function, it always returns
at least one chunk, and then checks for signals after each chunk. Chunk
sizes there are of length PAGE_SIZE. Let's just copy the same thing for
/dev/[u]random, and check for signals and cond_resched() for every
PAGE_SIZE amount of data. This makes the behavior more consistent with
expectations, and should mitigate the impact of Jann's fix for the
age-old signal check bug.
---- test program ----
#include <unistd.h>
#include <signal.h>
#include <stdio.h>
#include <sys/random.h>
static unsigned char x[~0U];
static void handle(int) { }
int main(int argc, char *argv[])
{
pid_t pid = getpid(), child;
signal(SIGUSR1, handle);
if (!(child = fork())) {
for (;;)
kill(pid, SIGUSR1);
}
pause();
printf("interrupted after reading %zd bytes\n", getrandom(x, sizeof(x), 0));
kill(child, SIGTERM);
return 0;
}
Cc: Jann Horn <jannh@xxxxxxxxxx>
Cc: Theodore Ts'o <tytso@xxxxxxx>
Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/char/random.c | 41 ++++++++++++++++++++---------------------
1 file changed, 20 insertions(+), 21 deletions(-)
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -523,9 +523,7 @@ EXPORT_SYMBOL(get_random_bytes);
static ssize_t get_random_bytes_user(void __user *buf, size_t nbytes)
{
- bool large_request = nbytes > 256;
- ssize_t ret = 0;
- size_t len;
+ size_t len, left, ret = 0;
u32 chacha_state[CHACHA20_BLOCK_SIZE / sizeof(u32)];
u8 output[CHACHA20_BLOCK_SIZE];
@@ -537,46 +535,47 @@ static ssize_t get_random_bytes_user(voi
* bytes, in case userspace causes copy_to_user() below to sleep
* forever, so that we still retain forward secrecy in that case.
*/
- crng_make_state(chacha_state, (u8 *)&chacha_state[4], CHACHA_KEY_SIZE);
+ crng_make_state(chacha_state, (u8 *)&chacha_state[4], CHACHA20_KEY_SIZE);
/*
* However, if we're doing a read of len <= 32, we don't need to
* use chacha_state after, so we can simply return those bytes to
* the user directly.
*/
- if (nbytes <= CHACHA_KEY_SIZE) {
- ret = copy_to_user(buf, &chacha_state[4], nbytes) ? -EFAULT : nbytes;
+ if (nbytes <= CHACHA20_KEY_SIZE) {
+ ret = nbytes - copy_to_user(buf, &chacha_state[4], nbytes);
goto out_zero_chacha;
}
- do {
- if (large_request) {
- if (signal_pending(current)) {
- if (!ret)
- ret = -ERESTARTSYS;
- break;
- }
- cond_resched();
- }
-
+ for (;;) {
chacha20_block(chacha_state, output);
if (unlikely(chacha_state[12] == 0))
++chacha_state[13];
len = min_t(size_t, nbytes, CHACHA20_BLOCK_SIZE);
- if (copy_to_user(buf, output, len)) {
- ret = -EFAULT;
+ left = copy_to_user(buf, output, len);
+ if (left) {
+ ret += len - left;
break;
}
- nbytes -= len;
buf += len;
ret += len;
- } while (nbytes);
+ nbytes -= len;
+ if (!nbytes)
+ break;
+
+ BUILD_BUG_ON(PAGE_SIZE % CHACHA20_BLOCK_SIZE != 0);
+ if (ret % PAGE_SIZE == 0) {
+ if (signal_pending(current))
+ break;
+ cond_resched();
+ }
+ }
memzero_explicit(output, sizeof(output));
out_zero_chacha:
memzero_explicit(chacha_state, sizeof(chacha_state));
- return ret;
+ return ret ? ret : -EFAULT;
}
/*
Patches currently in stable-queue which might be from Jason@xxxxxxxxx are
queue-4.19/random-do-not-take-pool-spinlock-at-boot.patch
queue-4.19/random-remove-kernel.random.read_wakeup_threshold.patch
queue-4.19/random-simplify-arithmetic-function-flow-in-account.patch
queue-4.19/random-order-timer-entropy-functions-below-interrupt-functions.patch
queue-4.19/random-introduce-drain_entropy-helper-to-declutter-crng_reseed.patch
queue-4.19/random-fix-locking-in-crng_fast_load.patch
queue-4.19/random-cleanup-uuid-handling.patch
queue-4.19/random-group-userspace-read-write-functions.patch
queue-4.19/random-make-credit_entropy_bits-always-safe.patch
queue-4.19/latent_entropy-avoid-build-error-when-plugin-cflags-are-not-set.patch
queue-4.19/revert-hwrng-core-freeze-khwrng-thread-during-suspend.patch
queue-4.19/drivers-char-random.c-make-primary_crng-static.patch
queue-4.19/random-do-not-re-init-if-crng_reseed-completes-before-primary-init.patch
queue-4.19/random-use-proper-jiffies-comparison-macro.patch
queue-4.19/init-call-time_init-before-rand_initialize.patch
queue-4.19/random-split-primary-secondary-crng-init-paths.patch
queue-4.19/random-pull-add_hwgenerator_randomness-declaration-into-random.h.patch
queue-4.19/random-unify-early-init-crng-load-accounting.patch
queue-4.19/drivers-char-random.c-remove-unused-stuct-poolinfo-poolbits.patch
queue-4.19/random-use-blake2s-instead-of-sha1-in-extraction.patch
queue-4.19/random-convert-to-using-fops-write_iter.patch
queue-4.19/random-initialize-chacha20-constants-with-correct-endianness.patch
queue-4.19/random-remove-incomplete-last_data-logic.patch
queue-4.19/random-group-entropy-extraction-functions.patch
queue-4.19/random-add-proper-spdx-header.patch
queue-4.19/linux-random.h-remove-arch_has_random-arch_has_random_seed.patch
queue-4.19/random-rewrite-header-introductory-comment.patch
queue-4.19/random-make-dev-random-be-almost-like-dev-urandom.patch
queue-4.19/random-remove-ifdef-d-out-interrupt-bench.patch
queue-4.19/um-use-fallback-for-random_get_entropy-instead-of-zero.patch
queue-4.19/lib-crypto-sha1-re-roll-loops-to-reduce-code-size.patch
queue-4.19/random-tie-batched-entropy-generation-to-base_crng-generation.patch
queue-4.19/sparc-use-fallback-for-random_get_entropy-instead-of-zero.patch
queue-4.19/random-use-linear-min-entropy-accumulation-crediting.patch
queue-4.19/random-remove-batched-entropy-locking.patch
queue-4.19/xtensa-use-fallback-for-random_get_entropy-instead-of-zero.patch
queue-4.19/powerpc-remove-arch_has_random-arch_has_random_seed.patch
queue-4.19/fdt-add-support-for-rng-seed.patch
queue-4.19/random-continually-use-hwgenerator-randomness.patch
queue-4.19/random-access-input_pool_data-directly-rather-than-through-pointer.patch
queue-4.19/random-add-arch_get_random_-long_early.patch
queue-4.19/random-inline-leaves-of-rand_initialize.patch
queue-4.19/random-cleanup-poolinfo-abstraction.patch
queue-4.19/random-wire-up-fops-splice_-read-write-_iter.patch
queue-4.19/random-handle-latent-entropy-and-command-line-from-random_init.patch
queue-4.19/random-remove-use_input_pool-parameter-from-crng_reseed.patch
queue-4.19/random-credit-architectural-init-the-exact-amount.patch
queue-4.19/ia64-define-get_cycles-macro-for-arch-override.patch
queue-4.19/random-replace-custom-notifier-chain-with-standard-one.patch
queue-4.19/random-support-freezable-kthreads-in-add_hwgenerator_randomness.patch
queue-4.19/random-document-get_random_int-family.patch
queue-4.19/random-remove-the-blocking-pool.patch
queue-4.19/random-avoid-initializing-twice-in-credit-race.patch
queue-4.19/random-avoid-warnings-for-config_numa-builds.patch
queue-4.19/crypto-drbg-add-fips-140-2-ctrng-for-noise-source.patch
queue-4.19/random-mark-bootloader-randomness-code-as-__init.patch
queue-4.19/random-zero-buffer-after-reading-entropy-from-userspace.patch
queue-4.19/random-remove-whitespace-and-reorder-includes.patch
queue-4.19/random-ignore-grnd_random-in-getentropy-2.patch
queue-4.19/random-clear-fast-pool-crng-and-batches-in-cpuhp-bring-up.patch
queue-4.19/random-document-add_hwgenerator_randomness-with-other-input-functions.patch
queue-4.19/random-fix-typo-in-add_timer_randomness.patch
queue-4.19/random-do-crng-pre-init-loading-in-worker-rather-than-irq.patch
queue-4.19/powerpc-use-bool-in-archrandom.h.patch
queue-4.19/random-do-not-split-fast-init-input-in-add_hwgenerator_randomness.patch
queue-4.19/timekeeping-add-raw-clock-fallback-for-random_get_entropy.patch
queue-4.19/random-early-initialization-of-chacha-constants.patch
queue-4.19/crypto-drbg-prepare-for-more-fine-grained-tracking-of-seeding-state.patch
queue-4.19/random-delete-code-to-pull-data-into-pools.patch
queue-4.19/crypto-drbg-always-try-to-free-jitter-rng-instance.patch
queue-4.19/random-simplify-entropy-debiting.patch
queue-4.19/random-don-t-reset-crng_init_cnt-on-urandom_read.patch
queue-4.19/random-skip-fast_init-if-hwrng-provides-large-chunk-of-entropy.patch
queue-4.19/random-use-siphash-as-interrupt-entropy-accumulator.patch
queue-4.19/random-avoid-checking-crng_ready-twice-in-random_init.patch
queue-4.19/random-fix-soft-lockup-when-trying-to-read-from-an-uninitialized-blocking-pool.patch
queue-4.19/random-group-sysctl-functions.patch
queue-4.19/random-don-t-let-644-read-only-sysctls-be-written-to.patch
queue-4.19/random-document-crng_fast_key_erasure-destination-possibility.patch
queue-4.19/random-only-wake-up-writers-after-zap-if-threshold-was-passed.patch
queue-4.19/random-use-wait_event_freezable-in-add_hwgenerator_randomness.patch
queue-4.19/random-check-for-signal-and-try-earlier-when-generating-entropy.patch
queue-4.19/random-check-for-signals-every-page_size-chunk-of-dev-random.patch
queue-4.19/arm-use-fallback-for-random_get_entropy-instead-of-zero.patch
queue-4.19/random-absorb-fast-pool-into-input-pool-after-fast-load.patch
queue-4.19/random-give-sysctl_random_min_urandom_seed-a-more-sensible-value.patch
queue-4.19/crypto-blake2s-generic-c-library-implementation-and-selftest.patch
queue-4.19/random-cleanup-fractional-entropy-shift-constants.patch
queue-4.19/random-use-rdseed-instead-of-rdrand-in-entropy-extraction.patch
queue-4.19/random-move-rand_initialize-earlier.patch
queue-4.19/random-don-t-wake-crng_init_wait-when-crng_init-1.patch
queue-4.19/random-add-a-urandom_read_nowait-for-random-apis-that-don-t-warn.patch
queue-4.19/random-do-not-sign-extend-bytes-for-rotation-when-mixing.patch
queue-4.19/random-move-initialization-functions-out-of-hot-pages.patch
queue-4.19/random-remove-dead-code-left-over-from-blocking-pool.patch
queue-4.19/drivers-char-random.c-constify-poolinfo_table.patch
queue-4.19/crypto-drbg-track-whether-drbg-was-seeded-with-rng_is_initialized.patch
queue-4.19/random-use-computational-hash-for-entropy-extraction.patch
queue-4.19/random-add-and-use-pr_fmt.patch
queue-4.19/random-round-robin-registers-as-ulong-not-u32.patch
queue-4.19/random-always-wake-up-entropy-writers-after-extraction.patch
queue-4.19/s390-remove-arch_has_random-arch_has_random_seed.patch
queue-4.19/random-do-not-xor-rdrand-when-writing-into-dev-random.patch
queue-4.19/crypto-drbg-make-reseeding-from-get_random_bytes-synchronous.patch
queue-4.19/random-convert-to-entropy_bits-for-better-code-readability.patch
queue-4.19/char-random-add-a-newline-at-the-end-of-the-file.patch
queue-4.19/random-move-randomize_page-into-mm-where-it-belongs.patch
queue-4.19/random-only-call-crng_finalize_init-for-primary_crng.patch
queue-4.19/random-cleanup-integer-types.patch
queue-4.19/random-re-add-removed-comment-about-get_random_-u32-u64-reseeding.patch
queue-4.19/random-unify-cycles_t-and-jiffies-usage-and-types.patch
queue-4.19/random-insist-on-random_get_entropy-existing-in-order-to-simplify.patch
queue-4.19/random-group-initialization-wait-functions.patch
queue-4.19/linux-random.h-mark-config_arch_random-functions-__must_check.patch
queue-4.19/random-remove-unused-extract_entropy-reserved-argument.patch
queue-4.19/random-check-for-signal_pending-outside-of-need_resched-check.patch
queue-4.19/random-access-primary_pool-directly-rather-than-through-pointer.patch
queue-4.19/random-fix-sysctl-documentation-nits.patch
queue-4.19/random-remove-unused-tracepoints.patch
queue-4.19/random-only-read-from-dev-random-after-its-pool-has-received-128-bits.patch
queue-4.19/nios2-use-fallback-for-random_get_entropy-instead-of-zero.patch
queue-4.19/random-treat-bootloader-trust-toggle-the-same-way-as-cpu-trust-toggle.patch
queue-4.19/random-make-consistent-usage-of-crng_ready.patch
queue-4.19/lib-crypto-blake2s-move-hmac-construction-into-wireguard.patch
queue-4.19/parisc-define-get_cycles-macro-for-arch-override.patch
queue-4.19/x86-tsc-use-fallback-for-random_get_entropy-instead-of-zero.patch
queue-4.19/random-add-grnd_insecure-to-return-best-effort-non-cryptographic-bytes.patch
queue-4.19/crypto-drbg-move-dynamic-reseed_threshold-adjustments-to-__drbg_seed.patch
queue-4.19/random-check-for-signals-after-page-of-pool-writes.patch
queue-4.19/random-make-random_get_entropy-return-an-unsigned-long.patch
queue-4.19/random-check-for-crng_init-0-in-add_device_randomness.patch
queue-4.19/random-remove-unnecessary-unlikely.patch
queue-4.19/random-defer-fast-pool-mixing-to-worker.patch
queue-4.19/random-harmonize-crng-init-done-messages.patch
queue-4.19/crypto-blake2s-include-linux-bug.h-instead-of-asm-bug.h.patch
queue-4.19/random-use-static-branch-for-crng_ready.patch
queue-4.19/random-rather-than-entropy_store-abstraction-use-global.patch
queue-4.19/random-remove-extern-from-functions-in-header.patch
queue-4.19/siphash-use-one-source-of-truth-for-siphash-permutations.patch
queue-4.19/random-group-entropy-collection-functions.patch
queue-4.19/random-de-duplicate-input_pool-constants.patch
queue-4.19/random-mix-build-time-latent-entropy-into-pool-at-init.patch
queue-4.19/random-remove-useless-header-comment.patch
queue-4.19/linux-random.h-use-false-with-bool.patch
queue-4.19/maintainers-co-maintain-random.c.patch
queue-4.19/random-remove-outdated-int_max-6-check-in-urandom_read.patch
queue-4.19/m68k-use-fallback-for-random_get_entropy-instead-of-zero.patch
queue-4.19/alpha-define-get_cycles-macro-for-arch-override.patch
queue-4.19/random-mix-bootloader-randomness-into-pool.patch
queue-4.19/random-remove-some-dead-code-of-poolinfo.patch
queue-4.19/random-do-not-use-batches-when-crng_ready.patch
queue-4.19/crypto-drbg-always-seeded-with-sp800-90b-compliant-noise-source.patch
queue-4.19/s390-define-get_cycles-macro-for-arch-override.patch
queue-4.19/random-do-not-pretend-to-handle-premature-next-security-model.patch
queue-4.19/random-avoid-arch_get_random_seed_long-when-collecting-irq-randomness.patch
queue-4.19/random-use-is_enabled-config_numa-instead-of-ifdefs.patch
queue-4.19/random-avoid-superfluous-call-to-rdrand-in-crng-extraction.patch
queue-4.19/random-use-symbolic-constants-for-crng_init-states.patch
queue-4.19/random-reseed-more-often-immediately-after-booting.patch
queue-4.19/random-ensure-early-rdseed-goes-through-mixer-on-init.patch
queue-4.19/random-deobfuscate-irq-u32-u64-contributions.patch
queue-4.19/random-do-not-use-input-pool-from-hard-irqs.patch
queue-4.19/random-help-compiler-out-with-fast_mix-by-using-simpler-arguments.patch
queue-4.19/revert-random-use-static-branch-for-crng_ready.patch
queue-4.19/random-fix-crash-on-multiple-early-calls-to-add_bootloader_randomness.patch
queue-4.19/random-account-for-arch-randomness-in-bits.patch
queue-4.19/crypto-blake2s-adjust-include-guard-naming.patch
queue-4.19/random-do-not-allow-user-to-keep-crng-key-around-on-stack.patch
queue-4.19/x86-remove-arch_has_random-arch_has_random_seed.patch
queue-4.19/random-remove-ratelimiting-for-in-kernel-unseeded-randomness.patch
queue-4.19/random-remove-unused-irq_flags-argument-from-add_interrupt_randomness.patch
queue-4.19/random-prepend-remaining-pool-constants-with-pool_.patch
queue-4.19/powerpc-define-get_cycles-macro-for-arch-override.patch
queue-4.19/random-remove-unused-output_pool-constants.patch
queue-4.19/mips-use-fallback-for-random_get_entropy-instead-of-just-c0-random.patch
queue-4.19/random-use-hash-function-for-crng_slow_load.patch
queue-4.19/random-fix-typo-in-comments.patch
queue-4.19/random-use-proper-return-types-on-get_random_-int-long-_wait.patch
