random-sysctl-linux.c File Reference

#include "uv.h"
#include "internal.h"
#include <errno.h>
#include <string.h>
#include <syscall.h>
#include <unistd.h>

Go to the source code of this file.

Classes
struct	uv__sysctl_args

Functions
int	uv__random_sysctl (void *buf, size_t buflen)

Function Documentation

uv__random_sysctl()

int uv__random_sysctl	(	void *	buf,
		size_t	buflen
	)

Definition at line 43 of file random-sysctl-linux.c.

                                                {
  static int name[] = {1 /*CTL_KERN*/, 40 /*KERN_RANDOM*/, 6 /*RANDOM_UUID*/};
  struct uv__sysctl_args args;
  char uuid[16];
  char* p;
  char* pe;
  size_t n;
 
  p = buf;
  pe = p + buflen;
 
  while (p < pe) {
    memset(&args, 0, sizeof(args));
 
    args.name = name;
    args.nlen = ARRAY_SIZE(name);
    args.oldval = uuid;
    args.oldlenp = &n;
    n = sizeof(uuid);
 
    /* Emits a deprecation warning with some kernels but that seems like
     * an okay trade-off for the fallback of the fallback: this function is
     * only called when neither getrandom(2) nor /dev/urandom are available.
     * Fails with ENOSYS on kernels configured without CONFIG_SYSCTL_SYSCALL.
     * At least arm64 never had a _sysctl system call and therefore doesn't
     * have a SYS__sysctl define either.
     */
#ifdef SYS__sysctl
    if (syscall(SYS__sysctl, &args) == -1)
      return UV__ERR(errno);
#else
    {
      (void) &args;
      return UV_ENOSYS;
    }
#endif
 
    if (n != sizeof(uuid))
      return UV_EIO;  /* Can't happen. */
 
    /* uuid[] is now a type 4 UUID. Bytes 6 and 8 (counting from zero) contain
     * 4 and 5 bits of entropy, respectively. For ease of use, we skip those
     * and only use 14 of the 16 bytes.
     */
    uuid[6] = uuid[14];
    uuid[8] = uuid[15];
 
    n = pe - p;
    if (n > 14)
      n = 14;
 
    memcpy(p, uuid, n);
    p += n;
  }
 
  return 0;
}

References args, ARRAY_SIZE, buflen, count, len, memcpy(), memset(), n, name, NULL, p, req, syscall, and UV__ERR.

Referenced by uv__random().