| 1 | /* Implementation of getentropy based on the getrandom system call. |
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| 2 | Copyright (C) 2016-2022 Free Software Foundation, Inc. |
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| 3 | This file is part of the GNU C Library. |
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| 4 | |
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| 5 | The GNU C Library is free software; you can redistribute it and/or |
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| 6 | modify it under the terms of the GNU Lesser General Public |
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| 7 | License as published by the Free Software Foundation; either |
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| 8 | version 2.1 of the License, or (at your option) any later version. |
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| 9 | |
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| 10 | The GNU C Library is distributed in the hope that it will be useful, |
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| 11 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
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| 12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
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| 13 | Lesser General Public License for more details. |
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| 14 | |
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| 15 | You should have received a copy of the GNU Lesser General Public |
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| 16 | License along with the GNU C Library; if not, see |
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| 17 | <https://www.gnu.org/licenses/>. */ |
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| 18 | |
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| 19 | #include <sys/random.h> |
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| 20 | #include <assert.h> |
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| 21 | #include <errno.h> |
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| 22 | #include <unistd.h> |
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| 23 | #include <sysdep.h> |
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| 24 | |
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| 25 | /* Write LENGTH bytes of randomness starting at BUFFER. Return 0 on |
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| 26 | success and -1 on failure. */ |
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| 27 | int |
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| 28 | getentropy (void *buffer, size_t length) |
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| 29 | { |
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| 30 | /* The interface is documented to return EIO for buffer lengths |
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| 31 | longer than 256 bytes. */ |
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| 32 | if (length > 256) |
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| 33 | { |
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| 34 | __set_errno (EIO); |
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| 35 | return -1; |
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| 36 | } |
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| 37 | |
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| 38 | /* Try to fill the buffer completely. Even with the 256 byte limit |
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| 39 | above, we might still receive an EINTR error (when blocking |
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| 40 | during boot). */ |
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| 41 | void *end = buffer + length; |
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| 42 | while (buffer < end) |
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| 43 | { |
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| 44 | /* NB: No cancellation point. */ |
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| 45 | ssize_t bytes = INLINE_SYSCALL_CALL (getrandom, buffer, end - buffer, 0); |
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| 46 | if (bytes < 0) |
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| 47 | { |
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| 48 | if (errno == EINTR) |
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| 49 | /* Try again if interrupted by a signal. */ |
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| 50 | continue; |
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| 51 | else |
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| 52 | return -1; |
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| 53 | } |
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| 54 | if (bytes == 0) |
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| 55 | { |
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| 56 | /* No more bytes available. This should not happen under |
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| 57 | normal circumstances. */ |
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| 58 | __set_errno (EIO); |
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| 59 | return -1; |
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| 60 | } |
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| 61 | /* Try again in case of a short read. */ |
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| 62 | buffer += bytes; |
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| 63 | } |
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| 64 | return 0; |
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| 65 | } |
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| 66 | |
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