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authorWladimir J. van der Laan <laanwj@gmail.com>2017-02-21 17:36:37 +0100
committerWladimir J. van der Laan <laanwj@gmail.com>2017-02-21 20:57:34 +0100
commit224e6eb089a0f4977d22f3803fc27e44b5e7eea5 (patch)
tree4bbac190c5858510347bc40f825d514a594c1d35 /configure.ac
parent5f0556d0326bf6f4d34f7e8b9ada7bbb09cb1df2 (diff)
util: Specific GetOSRandom for Linux/FreeBSD/OpenBSD
These are available in sandboxes without access to files or devices. Also [they are safer and more straightforward](https://en.wikipedia.org/wiki/Entropy-supplying_system_calls) to use than `/dev/urandom` as reading from a file has quite a few edge cases: - Linux: `getrandom(buf, buflen, 0)`. [getrandom(2)](http://man7.org/linux/man-pages/man2/getrandom.2.html) was introduced in version 3.17 of the Linux kernel. - OpenBSD: `getentropy(buf, buflen)`. The [getentropy(2)](http://man.openbsd.org/cgi-bin/man.cgi/OpenBSD-current/man2/getentropy.2) function appeared in OpenBSD 5.6. - FreeBSD and NetBSD: `sysctl(KERN_ARND)`. Not sure when this was added but it has existed for quite a while. Alternatives: - Linux has sysctl `CTL_KERN` / `KERN_RANDOM` / `RANDOM_UUID` which gives 16 bytes of randomness. This may be available on older kernels, however [sysctl is deprecated on Linux](https://lwn.net/Articles/605392/) and even removed in some distros so we shouldn't use it. Add tests for `GetOSRand()`: - Test that no error happens (otherwise `RandFailure()` which aborts) - Test that all 32 bytes are overwritten (initialize with zeros, try multiple times) Discussion: - When to use these? Currently they are always used when available. Another option would be to use them only when `/dev/urandom` is not available. But this would mean these code paths receive less testing, and I'm not sure there is any reason to prefer `/dev/urandom`. Closes: #9676
Diffstat (limited to 'configure.ac')
-rw-r--r--configure.ac27
1 files changed, 27 insertions, 0 deletions
diff --git a/configure.ac b/configure.ac
index 78129fb202..e454c15f04 100644
--- a/configure.ac
+++ b/configure.ac
@@ -558,6 +558,33 @@ AC_LINK_IFELSE([AC_LANG_SOURCE([
]
)
+# Check for different ways of gathering OS randomness
+AC_MSG_CHECKING(for Linux getrandom syscall)
+AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <unistd.h>
+ #include <sys/syscall.h>
+ #include <linux/random.h>]],
+ [[ syscall(SYS_getrandom, nullptr, 32, 0); ]])],
+ [ AC_MSG_RESULT(yes); AC_DEFINE(HAVE_SYS_GETRANDOM, 1,[Define this symbol if the Linux getrandom system call is available]) ],
+ [ 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 sysctl KERN_ARND)
+AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <sys/types.h>
+ #include <sys/sysctl.h>]],
+ [[ static const int name[2] = {CTL_KERN, KERN_ARND};
+ sysctl(name, 2, nullptr, nullptr, nullptr, 0); ]])],
+ [ AC_MSG_RESULT(yes); AC_DEFINE(HAVE_SYSCTL_ARND, 1,[Define this symbol if the BSD sysctl(KERN_ARND) is available]) ],
+ [ AC_MSG_RESULT(no)]
+)
+
+# Check for reduced exports
if test x$use_reduce_exports = xyes; then
AX_CHECK_COMPILE_FLAG([-fvisibility=hidden],[RE_CXXFLAGS="-fvisibility=hidden"],
[AC_MSG_ERROR([Cannot set default symbol visibility. Use --disable-reduce-exports.])])