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Jason A. Donenfeld 1805d20dfb random: check for signals every PAGE_SIZE chunk of /dev/[u]random 
commit e3c1c4fd9e upstream.

In 1448769c9c ("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@google.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2022-05-30 09:33:39 +02:00
arch random: remove unused irq_flags argument from add_interrupt_randomness() 2022-05-30 09:33:27 +02:00
block block-map: add __GFP_ZERO flag for alloc_page in function bio_copy_kern 2022-05-12 12:25:45 +02:00
certs certs: Trigger creation of RSA module signing key if it's not an RSA key 2021-09-15 09:50:29 +02:00
crypto random: replace custom notifier chain with standard one 2022-05-30 09:33:38 +02:00
Documentation random: treat bootloader trust toggle the same way as cpu trust toggle 2022-05-30 09:33:38 +02:00
drivers random: check for signals every PAGE_SIZE chunk of /dev/[u]random 2022-05-30 09:33:39 +02:00
fs afs: Fix afs_getattr() to refetch file status if callback break occurred 2022-05-25 09:18:01 +02:00
include random: replace custom notifier chain with standard one 2022-05-30 09:33:38 +02:00
init init/main.c: return 1 from handled __setup() functions 2022-04-13 21:01:01 +02:00
ipc shm: extend forced shm destroy to support objects from several IPC nses 2021-12-01 09:19:10 +01:00
kernel random: clear fast pool, crng, and batches in cpuhp bring up 2022-05-30 09:33:36 +02:00
lib random: replace custom notifier chain with standard one 2022-05-30 09:33:38 +02:00
LICENSES LICENSES/deprecated: add Zlib license text 2020-09-16 14:33:49 +02:00
mm mm: userfaultfd: fix missing cache flush in mcopy_atomic_pte() and __mcopy_atomic() 2022-05-15 20:00:09 +02:00
net secure_seq: use the 64 bits of the siphash for port offset calculation 2022-05-30 09:33:23 +02:00
samples samples/bpf, xdpsock: Fix race when running for fix duration of time 2022-04-08 14:40:21 +02:00
scripts gcc-plugins: latent_entropy: use /dev/urandom 2022-04-20 09:23:26 +02:00
security lockdown: also lock down previous kgdb use 2022-05-30 09:33:22 +02:00
sound ALSA: hda/realtek: Add quirk for TongFang devices with pop noise 2022-05-25 09:17:55 +02:00
tools selftests: add ping test with ping_group_range tuned 2022-05-25 09:18:00 +02:00
usr usr/include/Makefile: add linux/nfc.h to the compile-test coverage 2022-02-01 17:25:48 +01:00
virt KVM: Prevent module exit until all VMs are freed 2022-04-08 14:40:38 +02:00
.clang-format RDMA 5.10 pull request 2020-10-17 11:18:18 -07:00
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore kbuild: generate Module.symvers only when vmlinux exists 2021-05-19 10:12:59 +02:00
.mailmap mailmap: add two more addresses of Uwe Kleine-König 2020-12-06 10:19:07 -08:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Jason Cooper to CREDITS 2020-11-30 10:20:34 +01:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS MAINTAINERS: add git tree for random.c 2022-05-30 09:33:24 +02:00
Makefile Linux 5.10.118 2022-05-25 09:18:02 +02:00
README

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.