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glibc/include/stdlib.h
Jason A. Donenfeld eaad4f9e8f arc4random: simplify design for better safety 
Rather than buffering 16 MiB of entropy in userspace (by way of
chacha20), simply call getrandom() every time.

This approach is doubtlessly slower, for now, but trying to prematurely
optimize arc4random appears to be leading toward all sorts of nasty
properties and gotchas. Instead, this patch takes a much more
conservative approach. The interface is added as a basic loop wrapper
around getrandom(), and then later, the kernel and libc together can
work together on optimizing that.

This prevents numerous issues in which userspace is unaware of when it
really must throw away its buffer, since we avoid buffering all
together. Future improvements may include userspace learning more from
the kernel about when to do that, which might make these sorts of
chacha20-based optimizations more possible. The current heuristic of 16
MiB is meaningless garbage that doesn't correspond to anything the
kernel might know about. So for now, let's just do something
conservative that we know is correct and won't lead to cryptographic
issues for users of this function.

This patch might be considered along the lines of, "optimization is the
root of all evil," in that the much more complex implementation it
replaces moves too fast without considering security implications,
whereas the incremental approach done here is a much safer way of going
about things. Once this lands, we can take our time in optimizing this
properly using new interplay between the kernel and userspace.

getrandom(0) is used, since that's the one that ensures the bytes
returned are cryptographically secure. But on systems without it, we
fallback to using /dev/urandom. This is unfortunate because it means
opening a file descriptor, but there's not much of a choice. Secondly,
as part of the fallback, in order to get more or less the same
properties of getrandom(0), we poll on /dev/random, and if the poll
succeeds at least once, then we assume the RNG is initialized. This is a
rough approximation, as the ancient "non-blocking pool" initialized
after the "blocking pool", not before, and it may not port back to all
ancient kernels, though it does to all kernels supported by glibc
(≥3.2), so generally it's the best approximation we can do.

The motivation for including arc4random, in the first place, is to have
source-level compatibility with existing code. That means this patch
doesn't attempt to litigate the interface itself. It does, however,
choose a conservative approach for implementing it.

Cc: Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>
Cc: Florian Weimer <fweimer@redhat.com>
Cc: Cristian Rodríguez <crrodriguez@opensuse.org>
Cc: Paul Eggert <eggert@cs.ucla.edu>
Cc: Mark Harris <mark.hsj@gmail.com>
Cc: Eric Biggers <ebiggers@kernel.org>
Cc: linux-crypto@vger.kernel.org
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>
2022-07-27 08:58:27 -03:00

334 lines
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#ifndef _STDLIB_H
#ifndef _ISOMAC
# include <stddef.h>
#endif
/* Workaround PR90731 with GCC 9 when using ldbl redirects in C++. */
#include <bits/floatn.h>
#if defined __cplusplus && __LDOUBLE_REDIRECTS_TO_FLOAT128_ABI == 1
# if __GNUC_PREREQ (9, 0) && !__GNUC_PREREQ (9, 3)
# pragma GCC system_header
# endif
#endif
#include <stdlib/stdlib.h>
/* Now define the internal interfaces. */
#if !defined _ISOMAC
# include <sys/stat.h>
# include <rtld-malloc.h>
extern __typeof (strtol_l) __strtol_l;
extern __typeof (strtoul_l) __strtoul_l;
extern __typeof (strtoll_l) __strtoll_l;
extern __typeof (strtoull_l) __strtoull_l;
extern __typeof (strtod_l) __strtod_l;
extern __typeof (strtof_l) __strtof_l;
extern __typeof (strtold_l) __strtold_l;
libc_hidden_proto (__strtol_l)
libc_hidden_proto (__strtoul_l)
libc_hidden_proto (__strtoll_l)
libc_hidden_proto (__strtoull_l)
libc_hidden_proto (__strtod_l)
libc_hidden_proto (__strtof_l)
libc_hidden_proto (__strtold_l)
libc_hidden_proto (exit)
libc_hidden_proto (abort)
libc_hidden_proto (getenv)
extern __typeof (secure_getenv) __libc_secure_getenv;
libc_hidden_proto (__libc_secure_getenv)
libc_hidden_proto (bsearch)
libc_hidden_proto (qsort)
extern __typeof (qsort_r) __qsort_r;
libc_hidden_proto (__qsort_r)
libc_hidden_proto (lrand48_r)
libc_hidden_proto (wctomb)
extern long int __random (void) attribute_hidden;
extern void __srandom (unsigned int __seed);
extern char *__initstate (unsigned int __seed, char *__statebuf,
size_t __statelen);
extern char *__setstate (char *__statebuf);
extern int __random_r (struct random_data *__buf, int32_t *__result)
attribute_hidden;
extern int __srandom_r (unsigned int __seed, struct random_data *__buf)
attribute_hidden;
extern int __initstate_r (unsigned int __seed, char *__statebuf,
size_t __statelen, struct random_data *__buf)
attribute_hidden;
extern int __setstate_r (char *__statebuf, struct random_data *__buf)
attribute_hidden;
extern int __rand_r (unsigned int *__seed);
extern int __erand48_r (unsigned short int __xsubi[3],
struct drand48_data *__buffer, double *__result)
attribute_hidden;
extern int __nrand48_r (unsigned short int __xsubi[3],
struct drand48_data *__buffer,
long int *__result) attribute_hidden;
extern int __jrand48_r (unsigned short int __xsubi[3],
struct drand48_data *__buffer,
long int *__result) attribute_hidden;
extern int __srand48_r (long int __seedval,
struct drand48_data *__buffer) attribute_hidden;
extern int __seed48_r (unsigned short int __seed16v[3],
struct drand48_data *__buffer) attribute_hidden;
extern int __lcong48_r (unsigned short int __param[7],
struct drand48_data *__buffer) attribute_hidden;
/* Internal function to compute next state of the generator. */
extern int __drand48_iterate (unsigned short int __xsubi[3],
struct drand48_data *__buffer)
attribute_hidden;
/* Global state for non-reentrant functions. Defined in drand48-iter.c. */
extern struct drand48_data __libc_drand48_data attribute_hidden;
extern int __setenv (const char *__name, const char *__value, int __replace)
attribute_hidden;
extern int __unsetenv (const char *__name) attribute_hidden;
extern int __clearenv (void) attribute_hidden;
extern char *__mktemp (char *__template) __THROW __nonnull ((1));
libc_hidden_proto (__mktemp)
extern char *__canonicalize_file_name (const char *__name);
extern char *__realpath (const char *__name, char *__resolved);
libc_hidden_proto (__realpath)
extern int __ptsname_r (int __fd, char *__buf, size_t __buflen)
attribute_hidden;
# ifndef _ISOMAC
extern int __ptsname_internal (int fd, char *buf, size_t buflen,
struct stat64 *stp) attribute_hidden;
# endif
extern int __getpt (void);
extern int __posix_openpt (int __oflag) attribute_hidden;
extern int __add_to_environ (const char *name, const char *value,
const char *combines, int replace)
attribute_hidden;
extern void _quicksort (void *const pbase, size_t total_elems,
size_t size, __compar_d_fn_t cmp, void *arg);
extern int __on_exit (void (*__func) (int __status, void *__arg), void *__arg);
extern int __cxa_atexit (void (*func) (void *), void *arg, void *d);
libc_hidden_proto (__cxa_atexit);
extern int __cxa_thread_atexit_impl (void (*func) (void *), void *arg,
void *d);
extern void __call_tls_dtors (void)
#ifndef SHARED
__attribute__ ((weak))
#endif
;
libc_hidden_proto (__call_tls_dtors)
extern void __cxa_finalize (void *d);
extern int __posix_memalign (void **memptr, size_t alignment, size_t size);
extern void *__libc_memalign (size_t alignment, size_t size)
__attribute_malloc__;
extern void *__libc_reallocarray (void *__ptr, size_t __nmemb, size_t __size)
__THROW __attribute_warn_unused_result__;
libc_hidden_proto (__libc_reallocarray)
extern int __libc_system (const char *line);
extern __typeof (getpt) __getpt;
extern __typeof (ptsname_r) __ptsname_r;
libc_hidden_proto (__getpt)
libc_hidden_proto (__ptsname_r)
libc_hidden_proto (grantpt)
libc_hidden_proto (unlockpt)
__typeof (arc4random) __arc4random;
libc_hidden_proto (__arc4random);
__typeof (arc4random_buf) __arc4random_buf;
libc_hidden_proto (__arc4random_buf);
__typeof (arc4random_uniform) __arc4random_uniform;
libc_hidden_proto (__arc4random_uniform);
extern void __arc4random_buf_internal (void *buffer, size_t len)
attribute_hidden;
extern double __strtod_internal (const char *__restrict __nptr,
char **__restrict __endptr, int __group)
__THROW __nonnull ((1)) __wur;
extern float __strtof_internal (const char *__restrict __nptr,
char **__restrict __endptr, int __group)
__THROW __nonnull ((1)) __wur;
extern long double __strtold_internal (const char *__restrict __nptr,
char **__restrict __endptr,
int __group)
__THROW __nonnull ((1)) __wur;
extern long int __strtol_internal (const char *__restrict __nptr,
char **__restrict __endptr,
int __base, int __group)
__THROW __nonnull ((1)) __wur;
extern unsigned long int __strtoul_internal (const char *__restrict __nptr,
char **__restrict __endptr,
int __base, int __group)
__THROW __nonnull ((1)) __wur;
__extension__
extern long long int __strtoll_internal (const char *__restrict __nptr,
char **__restrict __endptr,
int __base, int __group)
__THROW __nonnull ((1)) __wur;
__extension__
extern unsigned long long int __strtoull_internal (const char *
__restrict __nptr,
char **__restrict __endptr,
int __base, int __group)
__THROW __nonnull ((1)) __wur;
libc_hidden_proto (__strtof_internal)
libc_hidden_proto (__strtod_internal)
libc_hidden_proto (__strtold_internal)
libc_hidden_proto (__strtol_internal)
libc_hidden_proto (__strtoll_internal)
libc_hidden_proto (__strtoul_internal)
libc_hidden_proto (__strtoull_internal)
extern double ____strtod_l_internal (const char *__restrict __nptr,
char **__restrict __endptr, int __group,
locale_t __loc);
extern float ____strtof_l_internal (const char *__restrict __nptr,
char **__restrict __endptr, int __group,
locale_t __loc);
extern long double ____strtold_l_internal (const char *__restrict __nptr,
char **__restrict __endptr,
int __group, locale_t __loc);
extern long int ____strtol_l_internal (const char *__restrict __nptr,
char **__restrict __endptr,
int __base, int __group,
locale_t __loc);
extern unsigned long int ____strtoul_l_internal (const char *
__restrict __nptr,
char **__restrict __endptr,
int __base, int __group,
locale_t __loc);
__extension__
extern long long int ____strtoll_l_internal (const char *__restrict __nptr,
char **__restrict __endptr,
int __base, int __group,
locale_t __loc);
__extension__
extern unsigned long long int ____strtoull_l_internal (const char *
__restrict __nptr,
char **
__restrict __endptr,
int __base, int __group,
locale_t __loc);
libc_hidden_proto (____strtof_l_internal)
libc_hidden_proto (____strtod_l_internal)
libc_hidden_proto (____strtold_l_internal)
libc_hidden_proto (____strtol_l_internal)
libc_hidden_proto (____strtoll_l_internal)
libc_hidden_proto (____strtoul_l_internal)
libc_hidden_proto (____strtoull_l_internal)
#include <bits/floatn.h>
libc_hidden_proto (strtof)
libc_hidden_proto (strtod)
#if __LDOUBLE_REDIRECTS_TO_FLOAT128_ABI == 0
libc_hidden_proto (strtold)
#endif
libc_hidden_proto (strtol)
libc_hidden_proto (strtoll)
libc_hidden_proto (strtoul)
libc_hidden_proto (strtoull)
libc_hidden_proto (atoi)
extern float __strtof_nan (const char *, char **, char);
extern double __strtod_nan (const char *, char **, char);
extern long double __strtold_nan (const char *, char **, char);
extern float __wcstof_nan (const wchar_t *, wchar_t **, wchar_t);
extern double __wcstod_nan (const wchar_t *, wchar_t **, wchar_t);
extern long double __wcstold_nan (const wchar_t *, wchar_t **, wchar_t);
libc_hidden_proto (__strtof_nan)
libc_hidden_proto (__strtod_nan)
libc_hidden_proto (__strtold_nan)
libc_hidden_proto (__wcstof_nan)
libc_hidden_proto (__wcstod_nan)
libc_hidden_proto (__wcstold_nan)
/* Enable _FloatN bits as needed. */
#include <bits/floatn.h>
#if __HAVE_DISTINCT_FLOAT128
extern __typeof (strtof128_l) __strtof128_l;
libc_hidden_proto (__strtof128_l)
libc_hidden_proto (strtof128)
extern _Float128 __strtof128_nan (const char *, char **, char);
extern _Float128 __wcstof128_nan (const wchar_t *, wchar_t **, wchar_t);
libc_hidden_proto (__strtof128_nan)
libc_hidden_proto (__wcstof128_nan)
extern _Float128 __strtof128_internal (const char *__restrict __nptr,
char **__restrict __endptr,
int __group);
libc_hidden_proto (__strtof128_internal)
extern _Float128 ____strtof128_l_internal (const char *__restrict __nptr,
char **__restrict __endptr,
int __group, locale_t __loc);
libc_hidden_proto (____strtof128_l_internal)
#endif
extern char *__ecvt (double __value, int __ndigit, int *__restrict __decpt,
int *__restrict __sign);
extern char *__fcvt (double __value, int __ndigit, int *__restrict __decpt,
int *__restrict __sign);
extern char *__gcvt (double __value, int __ndigit, char *__buf);
extern int __ecvt_r (double __value, int __ndigit, int *__restrict __decpt,
int *__restrict __sign, char *__restrict __buf,
size_t __len);
libc_hidden_proto (__ecvt_r)
extern int __fcvt_r (double __value, int __ndigit, int *__restrict __decpt,
int *__restrict __sign, char *__restrict __buf,
size_t __len);
libc_hidden_proto (__fcvt_r)
extern char *__qecvt (long double __value, int __ndigit,
int *__restrict __decpt, int *__restrict __sign);
extern char *__qfcvt (long double __value, int __ndigit,
int *__restrict __decpt, int *__restrict __sign);
extern char *__qgcvt (long double __value, int __ndigit, char *__buf);
extern int __qecvt_r (long double __value, int __ndigit,
int *__restrict __decpt, int *__restrict __sign,
char *__restrict __buf, size_t __len);
libc_hidden_proto (__qecvt_r)
extern int __qfcvt_r (long double __value, int __ndigit,
int *__restrict __decpt, int *__restrict __sign,
char *__restrict __buf, size_t __len);
libc_hidden_proto (__qfcvt_r)
# if IS_IN (libc)
# undef MB_CUR_MAX
# define MB_CUR_MAX (_NL_CURRENT_WORD (LC_CTYPE, _NL_CTYPE_MB_CUR_MAX))
# endif
struct abort_msg_s
{
unsigned int size;
char msg[0];
};
extern struct abort_msg_s *__abort_msg;
libc_hidden_proto (__abort_msg)
# if IS_IN (rtld)
extern __typeof (unsetenv) unsetenv attribute_hidden;
extern __typeof (__strtoul_internal) __strtoul_internal attribute_hidden;
# endif
#endif
#endif /* include/stdlib.h */
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