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util: Add general low-level random bytes helper
Currently secret_init() open codes getting good quality random bytes from the OS, either via getrandom(2) or reading /dev/random. We're going to add at least one more place that needs random data in future, so make a general helper for getting random bytes. While we're there, fix a number of minor bugs: - getrandom() can theoretically return a "short read", so handle that case - getrandom() as well as read can return a transient EINTR - We would attempt to read data from /dev/random if we failed to open it (open() returns -1), but not if we opened it as fd 0 (unlikely, but ok) - More specific error reporting Signed-off-by: David Gibson <david@gibson.dropbear.id.au> Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
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3 changed files with 57 additions and 29 deletions
54
util.c
54
util.c
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@ -34,6 +34,9 @@
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#include "passt.h"
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#include "packet.h"
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#include "log.h"
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#ifdef HAS_GETRANDOM
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#include <sys/random.h>
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#endif
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/**
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* sock_l4_sa() - Create and bind socket to socket address, add to epoll list
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@ -783,3 +786,54 @@ bool snprintf_check(char *str, size_t size, const char *format, ...)
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return false;
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}
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#define DEV_RANDOM "/dev/random"
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/**
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* raw_random() - Get high quality random bytes
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* @buf: Buffer to fill with random bytes
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* @buflen: Number of bytes of random data to put in @buf
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*
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* Assumes that the random data is essential, and will die() if unable to obtain
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* it.
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*/
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void raw_random(void *buf, size_t buflen)
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{
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size_t random_read = 0;
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#ifndef HAS_GETRANDOM
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int fd = open(DEV_RANDOM, O_RDONLY);
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if (fd < 0)
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die_perror("Couldn't open %s", DEV_RANDOM);
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#endif
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while (random_read < buflen) {
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ssize_t ret;
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#ifdef HAS_GETRANDOM
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ret = getrandom((char *)buf + random_read,
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buflen - random_read, GRND_RANDOM);
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#else
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ret = read(dev_random, (char *)buf + random_read,
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buflen - random_read);
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#endif
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if (ret == -1 && errno == EINTR)
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continue;
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if (ret < 0)
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die_perror("Error on random data source");
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if (ret == 0)
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break;
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random_read += ret;
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}
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#ifndef HAS_GETRANDOM
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close(dev_random);
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#endif
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if (random_read < buflen)
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die("Unexpected EOF on random data source");
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}
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