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patch 8.1.2343: using time() for srand() is not very random

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Problem:    Using time() for srand() is not very random.
Solution:   use /dev/urandom if available
This commit is contained in:
Bram Moolenaar 2019-11-26 12:23:30 +01:00
parent 06b0b4bc27
commit 07e4a19795
3 changed files with 50 additions and 5 deletions
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39
src/evalfunc.c
View File

@ -7095,10 +7095,45 @@ f_sqrt(typval_T *argvars, typval_T *rettv)
static void
f_srand(typval_T *argvars, typval_T *rettv)
{
static int dev_urandom_state = -1; // FAIL or OK once tried
if (rettv_list_alloc(rettv) == FAIL)
return;
if (argvars[0].v_type == VAR_UNKNOWN)
list_append_number(rettv->vval.v_list, (varnumber_T)vim_time());
{
if (dev_urandom_state != FAIL)
{
int fd = open("/dev/urandom", O_RDONLY);
struct {
union {
UINT32_T number;
char bytes[sizeof(UINT32_T)];
} cont;
} buf;
// Attempt reading /dev/urandom.
if (fd == -1)
dev_urandom_state = FAIL;
else
{
buf.cont.number = 0;
if (read(fd, buf.cont.bytes, sizeof(UINT32_T))
!= sizeof(UINT32_T))
dev_urandom_state = FAIL;
else
{
dev_urandom_state = OK;
list_append_number(rettv->vval.v_list,
(varnumber_T)buf.cont.number);
}
close(fd);
}
}
if (dev_urandom_state != OK)
// Reading /dev/urandom doesn't work, fall back to time().
list_append_number(rettv->vval.v_list, (varnumber_T)vim_time());
}
else
{
int error = FALSE;
@ -7107,7 +7142,7 @@ f_srand(typval_T *argvars, typval_T *rettv)
if (error)
return;
list_append_number(rettv->vval.v_list, x);
list_append_number(rettv->vval.v_list, (varnumber_T)x);
}
list_append_number(rettv->vval.v_list, 362436069);
list_append_number(rettv->vval.v_list, 521288629);

14
src/testdir/test_random.vim
View File

@ -11,9 +11,15 @@ func Test_Rand()
call test_settime(12341234)
let s = srand()
call assert_equal(s, srand())
call test_settime(12341235)
call assert_notequal(s, srand())
if filereadable('/dev/urandom')
" using /dev/urandom
call assert_notequal(s, srand())
else
" using time()
call assert_equal(s, srand())
call test_settime(12341235)
call assert_notequal(s, srand())
endif
call srand()
let v = rand()
@ -25,4 +31,6 @@ func Test_Rand()
call assert_fails('echo rand([1, [2], 3, 4])', 'E475:')
call assert_fails('echo rand([1, 2, [3], 4])', 'E475:')
call assert_fails('echo rand([1, 2, 3, [4]])', 'E475:')
call test_settime(0)
endfunc

2
src/version.c
View File

@ -737,6 +737,8 @@ static char *(features[]) =
static int included_patches[] =
{ /* Add new patch number below this line */
/**/
2343,
/**/
2342,
/**/