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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
96 lines
2.9 KiB
C
96 lines
2.9 KiB
C
/* Uncancelable versions of cancelable interfaces. Hurd version.
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Copyright (C) 2003-2022 Free Software Foundation, Inc.
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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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#include <sys/wait.h>
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#include <time.h>
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#include <sys/uio.h>
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#include <hurd.h>
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#include <hurd/fd.h>
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/* Non cancellable close syscall. */
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__typeof (__close) __close_nocancel;
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void __close_nocancel_nostatus (int fd);
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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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/* 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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/* 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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/* 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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/* Non cancellable wait4 syscall. */
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__typeof (__wait4) __wait4_nocancel;
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# define __waitpid_nocancel(pid, stat_loc, options) \
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__wait4_nocancel (pid, stat_loc, options, NULL)
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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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#define __getrandom_nocancel(buf, size, flags) \
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__getrandom (buf, size, flags)
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#if IS_IN (libc)
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hidden_proto (__close_nocancel)
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hidden_proto (__close_nocancel_nostatus)
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hidden_proto (__open_nocancel)
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hidden_proto (__openat_nocancel)
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hidden_proto (__read_nocancel)
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hidden_proto (__pread64_nocancel)
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hidden_proto (__write_nocancel)
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hidden_proto (__pwrite64_nocancel)
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hidden_proto (__writev_nocancel)
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hidden_proto (__writev_nocancel_nostatus)
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hidden_proto (__wait4_nocancel)
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hidden_proto (__fcntl_nocancel)
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#endif
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#endif /* NOT_CANCEL_H */
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