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@ -1,4 +1,4 @@ |
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/* $OpenBSD: getentropy_linux.c,v 1.1 2014/06/20 19:08:11 beck Exp $ */ |
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/* $OpenBSD: getentropy_linux.c,v 1.2 2014/06/20 19:53:36 otto Exp $ */ |
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/* |
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* Copyright (c) 2014 Theo de Raadt <deraadt@openbsd.org> |
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@ -61,8 +61,86 @@ |
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int getentropy(void *buf, size_t len); |
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extern int main(int, char *argv[]); |
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static int gotdata(char *buf, size_t len); |
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static int getentropy_urandom(void *buf, size_t len); |
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static int getentropy_sysctl(void *buf, size_t len); |
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static int getentropy_fallback(void *buf, size_t len); |
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int |
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getentropy(void *buf, size_t len) |
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{ |
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int ret = -1; |
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if (len > 256) { |
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errno = EIO; |
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return -1; |
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} |
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/* |
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* Try to get entropy with /dev/urandom |
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* |
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* This can fail if the process is inside a chroot or if file |
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* descriptors are exhausted. |
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*/ |
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ret = getentropy_urandom(buf, len); |
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if (ret != -1) |
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return (ret); |
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#ifdef RANDOM_UUID |
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/* |
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* Try to use sysctl CTL_KERN, KERN_RANDOM, RANDOM_UUID. sysctl is |
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* a failsafe API, so it guarantees a result. This should work |
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* inside a chroot, or when file descriptors are exhuasted. |
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* |
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* However this can fail if the Linux kernel removes support for sysctl. |
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* Starting in 2007, there have been efforts to deprecate the sysctl |
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* API/ABI, and push callers towards use of the chroot-unavailable |
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* fd-using /proc mechanism -- essentially the same problems as |
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* /dev/urandom. |
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* |
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* Numerous setbacks have been encountered in their deprecation |
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* schedule, so as of June 2014 the kernel ABI still exists. The |
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* sysctl() stub in libc is missing on some systems. There are |
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* also reports that some kernels spew messages to the console. |
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*/ |
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ret = getentropy_sysctl(buf, len); |
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if (ret != -1) |
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return (ret); |
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#endif /* RANDOM_UUID */ |
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/* |
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* Entropy collection via /dev/urandom and sysctl have failed. |
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* |
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* No other API exists for collecting entropy. See the large |
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* comment block above. |
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* |
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* We have very few options: |
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* - Even syslog_r is unsafe to call at this low level, so |
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* there is no way to alert the user or program. |
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* - Cannot call abort() because some systems have unsafe corefiles. |
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* - Could raise(SIGKILL) resulting in silent program termination. |
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* - Return EIO, to hint that arc4random's stir function |
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* should raise(SIGKILL) |
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* - Do the best under the circumstances.... |
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* |
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* This code path exists to bring light to the issue that Linux |
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* does not provide a failsafe API for entropy collection. |
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* |
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* We hope this demonstrates that Linux should either retain their |
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* sysctl ABI, or consider providing a new failsafe API which |
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* works in a chroot or when file descriptors are exhausted. |
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*/ |
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#undef FAIL_HARD_WHEN_LINUX_DEPRECATES_SYSCTL |
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#ifdef FAIL_HARD_WHEN_LINUX_DEPRECATES_SYSCTL |
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raise(SIGKILL); |
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#endif |
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ret = getentropy_fallback(buf, len); |
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if (ret != -1) |
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return (ret); |
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errno = EIO; |
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return (ret); |
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} |
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/* |
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* XXX Should be replaced with a proper entropy measure. |
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@ -361,79 +439,3 @@ getentropy_fallback(void *buf, size_t len) |
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errno = EIO; |
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return -1; |
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} |
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int |
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getentropy(void *buf, size_t len) |
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{ |
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int ret = -1; |
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if (len > 256) { |
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errno = EIO; |
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return -1; |
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} |
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/* |
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* Try to get entropy with /dev/urandom |
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* |
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* This can fail if the process is inside a chroot or if file |
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* descriptors are exhausted. |
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*/ |
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ret = getentropy_urandom(buf, len); |
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if (ret != -1) |
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return (ret); |
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#ifdef RANDOM_UUID |
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/* |
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* Try to use sysctl CTL_KERN, KERN_RANDOM, RANDOM_UUID. sysctl is |
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* a failsafe API, so it guarantees a result. This should work |
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* inside a chroot, or when file descriptors are exhuasted. |
|
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|
* |
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* However this can fail if the Linux kernel removes support for sysctl. |
|
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|
* Starting in 2007, there have been efforts to deprecate the sysctl |
|
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|
* API/ABI, and push callers towards use of the chroot-unavailable |
|
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|
* fd-using /proc mechanism -- essentially the same problems as |
|
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|
* /dev/urandom. |
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* |
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* Numerous setbacks have been encountered in their deprecation |
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|
* schedule, so as of June 2014 the kernel ABI still exists. The |
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* sysctl() stub in libc is missing on some systems. There are |
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* also reports that some kernels spew messages to the console. |
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*/ |
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ret = getentropy_sysctl(buf, len); |
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if (ret != -1) |
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return (ret); |
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#endif /* RANDOM_UUID */ |
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/* |
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* Entropy collection via /dev/urandom and sysctl have failed. |
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|
* |
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|
* No other API exists for collecting entropy. See the large |
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|
* comment block above. |
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|
* |
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|
|
* We have very few options: |
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* - Even syslog_r is unsafe to call at this low level, so |
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* there is no way to alert the user or program. |
|
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|
* - Cannot call abort() because some systems have unsafe corefiles. |
|
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|
* - Could raise(SIGKILL) resulting in silent program termination. |
|
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* - Return EIO, to hint that arc4random's stir function |
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|
* should raise(SIGKILL) |
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|
* - Do the best under the circumstances.... |
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* |
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|
* This code path exists to bring light to the issue that Linux |
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* does not provide a failsafe API for entropy collection. |
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* |
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|
* We hope this demonstrates that Linux should either retain their |
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* sysctl ABI, or consider providing a new failsafe API which |
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* works in a chroot or when file descriptors are exhausted. |
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*/ |
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#undef FAIL_HARD_WHEN_LINUX_DEPRECATES_SYSCTL |
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#ifdef FAIL_HARD_WHEN_LINUX_DEPRECATES_SYSCTL |
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raise(SIGKILL); |
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#endif |
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ret = getentropy_fallback(buf, len); |
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if (ret != -1) |
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return (ret); |
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errno = EIO; |
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return (ret); |
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} |
otto
10 years ago