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Merge bitcoin/bitcoin#24238: random: use arc4random on OpenBSD

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0c49e52b22 build: remove unneeded getentropy detection (HAVE_GETENTROPY) (Sebastian Falbesoner)
5cd15ffdce random: use arc4random on OpenBSD (Sebastian Falbesoner)

Pull request description:

  Inspired by a discussion on obtaining randomness on various OSes in a secp256k1 PR (https://github.com/bitcoin-core/secp256k1/pull/748#discussion_r524605472, see also https://bitcoincore.reviews/libsecp256k1-748), I think it makes sense to follow best practices and use `arc4random_buf` rather than `getentropy` on OpenBSD in our random module.

  The [getentropy(2) man page](https://man.openbsd.org/getentropy.2) states:
  ```
  getentropy() is not intended for regular code; please use the
  arc4random(3) family of functions instead.
  ```

  The [arc4random(3) man page](https://man.openbsd.org/arc4random.3) states:

  ```
  Use of these functions is encouraged for almost all random number
  consumption because the other interfaces are deficient in either quality,
  portability, standardization, or availability.
  ```
  On the linked PR discussion worries about using RC4 internally has been expressed (see https://security.stackexchange.com/questions/85601/is-arc4random-secure-enough/172905#172905), but this would only affect users of OpenBSD <5.5, using a version that was released more than 8 years ago.

ACKs for top commit:
  laanwj:
    Tested ACK 0c49e52b22

Tree-SHA512: b5ed3d0718962c5a3839db9a28f93d08a0ac93094cc664f83bc4cf1cfad25049e6240b7b81fe06b71e6a3a0ca24a2c337eab088abec5470ad014e10c04fdb216
This commit is contained in:
laanwj 2022-02-10 10:00:46 +01:00
commit a7e80449c0
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GPG key ID: 1E4AED62986CD25D
2 changed files with 8 additions and 19 deletions
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7
configure.ac
View file

@ -1112,13 +1112,6 @@ AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <unistd.h>
[ AC_MSG_RESULT([no])]
)
AC_MSG_CHECKING([for getentropy])
AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <unistd.h>]],
[[ getentropy(nullptr, 32) ]])],
[ AC_MSG_RESULT([yes]); AC_DEFINE([HAVE_GETENTROPY], [1], [Define this symbol if the BSD getentropy system call is available]) ],
[ AC_MSG_RESULT([no])]
)
AC_MSG_CHECKING([for getentropy via random.h])
AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <unistd.h>
#include <sys/random.h>]],

20
src/random.cpp
View file

@ -32,10 +32,8 @@
#include <sys/syscall.h>
#include <linux/random.h>
#endif
#if defined(HAVE_GETENTROPY) || (defined(HAVE_GETENTROPY_RAND) && defined(MAC_OSX))
#include <unistd.h>
#endif
#if defined(HAVE_GETENTROPY_RAND) && defined(MAC_OSX)
#include <unistd.h>
#include <sys/random.h>
#endif
#ifdef HAVE_SYSCTL_ARND
@ -305,16 +303,14 @@ void GetOSRand(unsigned char *ent32)
RandFailure();
}
}
#elif defined(HAVE_GETENTROPY) && defined(__OpenBSD__)
/* On OpenBSD this can return up to 256 bytes of entropy, will return an
* error if more are requested.
* The call cannot return less than the requested number of bytes.
getentropy is explicitly limited to openbsd here, as a similar (but not
the same) function may exist on other platforms via glibc.
#elif defined(__OpenBSD__)
/* OpenBSD. From the arc4random(3) man page:
"Use of these functions is encouraged for almost all random number
consumption because the other interfaces are deficient in either
quality, portability, standardization, or availability."
The function call is always successful.
*/
if (getentropy(ent32, NUM_OS_RANDOM_BYTES) != 0) {
RandFailure();
}
arc4random_buf(ent32, NUM_OS_RANDOM_BYTES);
// Silence a compiler warning about unused function.
(void)GetDevURandom;
#elif defined(HAVE_GETENTROPY_RAND) && defined(MAC_OSX)