2019-12-13 02:23:14 +00:00
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/* Uncancelable versions of cancelable interfaces. Hurd version.
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2024-01-01 18:12:26 +00:00
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Copyright (C) 2003-2024 Free Software Foundation, Inc.
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2019-12-13 02:23:14 +00:00
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#ifndef NOT_CANCEL_H
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# define NOT_CANCEL_H
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#include <fcntl.h>
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#include <unistd.h>
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arc4random: simplify design for better safety
Rather than buffering 16 MiB of entropy in userspace (by way of
chacha20), simply call getrandom() every time.
This approach is doubtlessly slower, for now, but trying to prematurely
optimize arc4random appears to be leading toward all sorts of nasty
properties and gotchas. Instead, this patch takes a much more
conservative approach. The interface is added as a basic loop wrapper
around getrandom(), and then later, the kernel and libc together can
work together on optimizing that.
This prevents numerous issues in which userspace is unaware of when it
really must throw away its buffer, since we avoid buffering all
together. Future improvements may include userspace learning more from
the kernel about when to do that, which might make these sorts of
chacha20-based optimizations more possible. The current heuristic of 16
MiB is meaningless garbage that doesn't correspond to anything the
kernel might know about. So for now, let's just do something
conservative that we know is correct and won't lead to cryptographic
issues for users of this function.
This patch might be considered along the lines of, "optimization is the
root of all evil," in that the much more complex implementation it
replaces moves too fast without considering security implications,
whereas the incremental approach done here is a much safer way of going
about things. Once this lands, we can take our time in optimizing this
properly using new interplay between the kernel and userspace.
getrandom(0) is used, since that's the one that ensures the bytes
returned are cryptographically secure. But on systems without it, we
fallback to using /dev/urandom. This is unfortunate because it means
opening a file descriptor, but there's not much of a choice. Secondly,
as part of the fallback, in order to get more or less the same
properties of getrandom(0), we poll on /dev/random, and if the poll
succeeds at least once, then we assume the RNG is initialized. This is a
rough approximation, as the ancient "non-blocking pool" initialized
after the "blocking pool", not before, and it may not port back to all
ancient kernels, though it does to all kernels supported by glibc
(≥3.2), so generally it's the best approximation we can do.
The motivation for including arc4random, in the first place, is to have
source-level compatibility with existing code. That means this patch
doesn't attempt to litigate the interface itself. It does, however,
choose a conservative approach for implementing it.
Cc: Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>
Cc: Florian Weimer <fweimer@redhat.com>
Cc: Cristian Rodríguez <crrodriguez@opensuse.org>
Cc: Paul Eggert <eggert@cs.ucla.edu>
Cc: Mark Harris <mark.hsj@gmail.com>
Cc: Eric Biggers <ebiggers@kernel.org>
Cc: linux-crypto@vger.kernel.org
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
2022-07-26 19:58:22 +00:00
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#include <poll.h>
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2019-12-13 02:23:14 +00:00
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#include <sys/wait.h>
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#include <time.h>
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#include <sys/uio.h>
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2022-09-29 19:18:06 +00:00
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#include <sys/random.h>
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2019-12-13 02:23:14 +00:00
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#include <hurd.h>
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#include <hurd/fd.h>
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2020-06-28 15:51:40 +00:00
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/* Non cancellable close syscall. */
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__typeof (__close) __close_nocancel;
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2019-12-13 02:23:14 +00:00
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2019-12-13 02:32:21 +00:00
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void __close_nocancel_nostatus (int fd);
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2019-12-13 02:23:14 +00:00
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2020-06-28 14:27:36 +00:00
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/* Non cancellable open syscall. */
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__typeof (__open) __open_nocancel;
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/* open64 is just the same as open for us. */
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#define __open64_nocancel(...) \
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__open_nocancel (__VA_ARGS__)
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/* Non cancellable openat syscall. */
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__typeof (__openat) __openat_nocancel;
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/* open64 is just the same as open for us. */
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#define __openat64_nocancel(...) \
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__openat_nocancel (__VA_ARGS__)
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2020-06-07 23:16:46 +00:00
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/* Non cancellable read syscall. */
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__typeof (__read) __read_nocancel;
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/* Non cancellable pread syscall (LFS version). */
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__typeof (__pread64) __pread64_nocancel;
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2020-06-14 15:50:44 +00:00
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/* Non cancellable write syscall. */
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__typeof (__write) __write_nocancel;
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/* Non cancellable pwrite syscall (LFS version). */
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__typeof (__pwrite64) __pwrite64_nocancel;
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2020-06-14 17:44:57 +00:00
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/* Non cancellable writev syscall. */
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__typeof (__writev) __writev_nocancel;
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/* Non cancellable writev syscall with no status. */
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void __writev_nocancel_nostatus (int fd, const struct iovec *vector, int count);
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2020-06-28 16:54:49 +00:00
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/* Non cancellable wait4 syscall. */
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__typeof (__wait4) __wait4_nocancel;
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2019-12-13 02:23:14 +00:00
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# define __waitpid_nocancel(pid, stat_loc, options) \
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2020-06-28 16:54:49 +00:00
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__wait4_nocancel (pid, stat_loc, options, NULL)
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2020-06-28 18:18:43 +00:00
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/* Non cancellable fcntl syscall. */
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__typeof (__fcntl) __fcntl_nocancel;
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/* fcntl64 is just the same as fcntl for us. */
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#define __fcntl64_nocancel(...) \
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__fcntl_nocancel (__VA_ARGS__)
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2019-12-13 02:23:14 +00:00
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2024-01-04 13:41:20 +00:00
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/* Non cancellable getrandom syscall that does not also set errno in case of
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failure. */
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2022-09-29 19:18:06 +00:00
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static inline ssize_t
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2024-01-04 13:41:20 +00:00
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__getrandom_nocancel_nostatus (void *buf, size_t buflen, unsigned int flags)
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2022-09-29 19:18:06 +00:00
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{
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int save_errno = errno;
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ssize_t r = __getrandom (buf, buflen, flags);
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r = r == -1 ? -errno : r;
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__set_errno (save_errno);
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return r;
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}
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stdlib: Add arc4random, arc4random_buf, and arc4random_uniform (BZ #4417)
The implementation is based on scalar Chacha20 with per-thread cache.
It uses getrandom or /dev/urandom as fallback to get the initial entropy,
and reseeds the internal state on every 16MB of consumed buffer.
To improve performance and lower memory consumption the per-thread cache
is allocated lazily on first arc4random functions call, and if the
memory allocation fails getentropy or /dev/urandom is used as fallback.
The cache is also cleared on thread exit iff it was initialized (so if
arc4random is not called it is not touched).
Although it is lock-free, arc4random is still not async-signal-safe
(the per thread state is not updated atomically).
The ChaCha20 implementation is based on RFC8439 [1], omitting the final
XOR of the keystream with the plaintext because the plaintext is a
stream of zeros. This strategy is similar to what OpenBSD arc4random
does.
The arc4random_uniform is based on previous work by Florian Weimer,
where the algorithm is based on Jérémie Lumbroso paper Optimal Discrete
Uniform Generation from Coin Flips, and Applications (2013) [2], who
credits Donald E. Knuth and Andrew C. Yao, The complexity of nonuniform
random number generation (1976), for solving the general case.
The main advantage of this method is the that the unit of randomness is not
the uniform random variable (uint32_t), but a random bit. It optimizes the
internal buffer sampling by initially consuming a 32-bit random variable
and then sampling byte per byte. Depending of the upper bound requested,
it might lead to better CPU utilization.
Checked on x86_64-linux-gnu, aarch64-linux, and powerpc64le-linux-gnu.
Co-authored-by: Florian Weimer <fweimer@redhat.com>
Reviewed-by: Yann Droneaud <ydroneaud@opteya.com>
[1] https://datatracker.ietf.org/doc/html/rfc8439
[2] https://arxiv.org/pdf/1304.1916.pdf
2022-07-21 13:04:59 +00:00
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2024-01-04 13:41:20 +00:00
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#define __getrandom_nocancel(buf, size, flags) \
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__getrandom (buf, size, flags)
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arc4random: simplify design for better safety
Rather than buffering 16 MiB of entropy in userspace (by way of
chacha20), simply call getrandom() every time.
This approach is doubtlessly slower, for now, but trying to prematurely
optimize arc4random appears to be leading toward all sorts of nasty
properties and gotchas. Instead, this patch takes a much more
conservative approach. The interface is added as a basic loop wrapper
around getrandom(), and then later, the kernel and libc together can
work together on optimizing that.
This prevents numerous issues in which userspace is unaware of when it
really must throw away its buffer, since we avoid buffering all
together. Future improvements may include userspace learning more from
the kernel about when to do that, which might make these sorts of
chacha20-based optimizations more possible. The current heuristic of 16
MiB is meaningless garbage that doesn't correspond to anything the
kernel might know about. So for now, let's just do something
conservative that we know is correct and won't lead to cryptographic
issues for users of this function.
This patch might be considered along the lines of, "optimization is the
root of all evil," in that the much more complex implementation it
replaces moves too fast without considering security implications,
whereas the incremental approach done here is a much safer way of going
about things. Once this lands, we can take our time in optimizing this
properly using new interplay between the kernel and userspace.
getrandom(0) is used, since that's the one that ensures the bytes
returned are cryptographically secure. But on systems without it, we
fallback to using /dev/urandom. This is unfortunate because it means
opening a file descriptor, but there's not much of a choice. Secondly,
as part of the fallback, in order to get more or less the same
properties of getrandom(0), we poll on /dev/random, and if the poll
succeeds at least once, then we assume the RNG is initialized. This is a
rough approximation, as the ancient "non-blocking pool" initialized
after the "blocking pool", not before, and it may not port back to all
ancient kernels, though it does to all kernels supported by glibc
(≥3.2), so generally it's the best approximation we can do.
The motivation for including arc4random, in the first place, is to have
source-level compatibility with existing code. That means this patch
doesn't attempt to litigate the interface itself. It does, however,
choose a conservative approach for implementing it.
Cc: Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>
Cc: Florian Weimer <fweimer@redhat.com>
Cc: Cristian Rodríguez <crrodriguez@opensuse.org>
Cc: Paul Eggert <eggert@cs.ucla.edu>
Cc: Mark Harris <mark.hsj@gmail.com>
Cc: Eric Biggers <ebiggers@kernel.org>
Cc: linux-crypto@vger.kernel.org
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
2022-07-26 19:58:22 +00:00
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#define __poll_infinity_nocancel(fds, nfds) \
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__poll (fds, nfds, -1)
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2020-06-07 23:16:46 +00:00
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#if IS_IN (libc)
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2020-06-28 15:51:40 +00:00
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hidden_proto (__close_nocancel)
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hidden_proto (__close_nocancel_nostatus)
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2020-06-28 14:27:36 +00:00
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hidden_proto (__open_nocancel)
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hidden_proto (__openat_nocancel)
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2020-06-07 23:16:46 +00:00
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hidden_proto (__read_nocancel)
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hidden_proto (__pread64_nocancel)
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2020-06-14 15:50:44 +00:00
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hidden_proto (__write_nocancel)
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hidden_proto (__pwrite64_nocancel)
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2020-06-14 17:44:57 +00:00
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hidden_proto (__writev_nocancel)
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hidden_proto (__writev_nocancel_nostatus)
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2020-06-28 16:54:49 +00:00
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hidden_proto (__wait4_nocancel)
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2020-06-28 18:18:43 +00:00
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hidden_proto (__fcntl_nocancel)
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2019-12-13 02:32:21 +00:00
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#endif
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2019-12-13 02:23:14 +00:00
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#endif /* NOT_CANCEL_H */
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