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Make tempname more random, via the randint module.

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* gl/modules/tempname (Depends-on): Add randint and stdbool.
* gl/lib/tempname.c: Include randint.h and stdbool.h.
(uint64_t): Remove definition.  Not needed.
[_LIBC] (RANDOM_BITS): Remove this block, now that we have proper random bits.
(check_x_suffix): New function.
(gen_tempname_len): Rename from __gen_tempname.
Add a parameter, x_suffix_len, telling how many X's there must be at
the end of the template.
Use pseudo-random numbers all the way, rather than adding 7777
from one iteration to the next.
(__gen_tempname): New function, to call gen_tempname_len, requiring a
suffix length of 6.
* gl/lib/tempname.h: Add prototype for gen_tempname_len.

Signed-off-by: Jim Meyering <meyering@redhat.com>
This commit is contained in:
Jim Meyering
2007-09-01 10:33:33 +02:00
parent 58a7ead41d
commit 7eab7d027e
4 changed files with 77 additions and 70 deletions
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16
ChangeLog
View File

@@ -1,5 +1,21 @@
2007-10-07 Jim Meyering <meyering@redhat.com>
Make tempname more random, via the randint module.
* gl/modules/tempname (Depends-on): Add randint and stdbool.
* gl/lib/tempname.c: Include randint.h and stdbool.h.
(uint64_t): Remove definition. Not needed.
[_LIBC] (RANDOM_BITS): Remove this block, now that we have proper
random bits.
(check_x_suffix): New function.
(gen_tempname_len): Rename from __gen_tempname.
Add a parameter, x_suffix_len, telling how many X's there must be at
the end of the template.
Use pseudo-random numbers all the way, rather than adding 7777
from one iteration to the next.
(__gen_tempname): New function, to call gen_tempname_len, requiring a
suffix length of 6.
* gl/lib/tempname.h: Add prototype for gen_tempname_len.
Convert coreutils' rand*.{c,h,m4} into modules.
First step: move these files to gl/lib:
* lib/rand-isaac.c, lib/rand-isaac.h

123
gl/lib/tempname.c
View File

@@ -23,6 +23,7 @@
#if !_LIBC
# include <config.h>
# include "tempname.h"
# include "randint.h"
#endif
#include <sys/types.h>
@@ -47,6 +48,7 @@
# define __GT_NOCREATE 3
#endif
#include <stdbool.h>
#include <stddef.h>
#include <stdlib.h>
#include <string.h>
@@ -78,34 +80,6 @@
# define __secure_getenv getenv
#endif
#ifdef _LIBC
# include <hp-timing.h>
# if HP_TIMING_AVAIL
# define RANDOM_BITS(Var) \
if (__builtin_expect (value == UINT64_C (0), 0)) \
{ \
/* If this is the first time this function is used initialize \
the variable we accumulate the value in to some somewhat \
random value. If we'd not do this programs at startup time \
might have a reduced set of possible names, at least on slow \
machines. */ \
struct timeval tv; \
__gettimeofday (&tv, NULL); \
value = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec; \
} \
HP_TIMING_NOW (Var)
# endif
#endif
/* Use the widest available unsigned type if uint64_t is not
available. The algorithm below extracts a number less than 62**6
(approximately 2**35.725) from uint64_t, so ancient hosts where
uintmax_t is only 32 bits lose about 3.725 bits of randomness,
which is better than not having mkstemp at all. */
#if !defined UINT64_MAX && !defined uint64_t
# define uint64_t uintmax_t
#endif
#if _LIBC
/* Return nonzero if DIR is an existent directory. */
static int
@@ -179,12 +153,18 @@ __path_search (char *tmpl, size_t tmpl_len, const char *dir, const char *pfx,
}
#endif /* _LIBC */
static inline bool
check_x_suffix (char const *s, size_t len)
{
return strspn (s, "X") == len;
}
/* These are the characters used in temporary file names. */
static const char letters[] =
"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
/* Generate a temporary file name based on TMPL. TMPL must match the
rules for mk[s]temp (i.e. end in "XXXXXX"). The name constructed
/* Generate a temporary file name based on TMPL. TMPL must end in a
a sequence of at least X_SUFFIX_LEN "X"s. The name constructed
does not exist at the time of the call to __gen_tempname. TMPL is
overwritten with the result.
@@ -198,16 +178,15 @@ static const char letters[] =
We use a clever algorithm to get hard-to-predict names. */
int
__gen_tempname (char *tmpl, int kind)
gen_tempname_len (char *tmpl, int kind, size_t x_suffix_len)
{
int len;
size_t len;
char *XXXXXX;
static uint64_t value;
uint64_t random_time_bits;
unsigned int count;
int fd = -1;
int save_errno = errno;
struct_stat64 st;
struct randint_source *rand_src;
/* A lower bound on the number of temporary files to attempt to
generate. The maximum total number of temporary file names that
@@ -226,43 +205,28 @@ __gen_tempname (char *tmpl, int kind)
#endif
len = strlen (tmpl);
if (len < 6 || strcmp (&tmpl[len - 6], "XXXXXX"))
if (len < x_suffix_len || ! check_x_suffix (&tmpl[len - x_suffix_len],
x_suffix_len))
{
__set_errno (EINVAL);
return -1;
}
rand_src = randint_all_new (NULL, 8);
if (! rand_src)
return -1;
/* This is where the Xs start. */
XXXXXX = &tmpl[len - 6];
XXXXXX = &tmpl[len - x_suffix_len];
/* Get some more or less random data. */
#ifdef RANDOM_BITS
RANDOM_BITS (random_time_bits);
#else
{
struct timeval tv;
__gettimeofday (&tv, NULL);
random_time_bits = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec;
}
#endif
value += random_time_bits ^ __getpid ();
for (count = 0; count < attempts; value += 7777, ++count)
for (count = 0; count < attempts; ++count)
{
uint64_t v = value;
size_t i;
/* Fill in the random bits. */
XXXXXX[0] = letters[v % 62];
v /= 62;
XXXXXX[1] = letters[v % 62];
v /= 62;
XXXXXX[2] = letters[v % 62];
v /= 62;
XXXXXX[3] = letters[v % 62];
v /= 62;
XXXXXX[4] = letters[v % 62];
v /= 62;
XXXXXX[5] = letters[v % 62];
for (i = 0; i < x_suffix_len; i++)
{
XXXXXX[i] = letters[randint_genmax (rand_src, sizeof letters - 2)];
}
switch (kind)
{
@@ -279,7 +243,7 @@ __gen_tempname (char *tmpl, int kind)
break;
case __GT_NOCREATE:
/* This case is backward from the other three. __gen_tempname
/* This case is backward from the other three. This function
succeeds if __xstat fails because the name does not exist.
Note the continue to bypass the common logic at the bottom
of the loop. */
@@ -288,11 +252,15 @@ __gen_tempname (char *tmpl, int kind)
if (errno == ENOENT)
{
__set_errno (save_errno);
return 0;
fd = 0;
goto done;
}
else
/* Give up now. */
return -1;
{
/* Give up now. */
fd = -1;
goto done;
}
}
continue;
@@ -303,13 +271,32 @@ __gen_tempname (char *tmpl, int kind)
if (fd >= 0)
{
__set_errno (save_errno);
return fd;
goto done;
}
else if (errno != EEXIST)
return -1;
{
fd = -1;
goto done;
}
}
randint_all_free (rand_src);
/* We got out of the loop because we ran out of combinations to try. */
__set_errno (EEXIST);
return -1;
done:
{
int saved_errno = errno;
randint_all_free (rand_src);
__set_errno (saved_errno);
}
return fd;
}
int
__gen_tempname (char *tmpl, int kind)
{
return gen_tempname_len (tmpl, kind, 6);
}

4
gl/lib/tempname.h
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@@ -1,6 +1,6 @@
/* Create a temporary file or directory.
Copyright (C) 2006 Free Software Foundation, Inc.
Copyright (C) 2006, 2007 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
@@ -37,4 +37,6 @@
GT_DIR: create a directory, which will be mode 0700.
We use a clever algorithm to get hard-to-predict names. */
#include <stddef.h>
extern int gen_tempname (char *tmpl, int kind);
extern int gen_tempname_len (char *tmpl, int kind, size_t x_suffix_len);

4
gl/modules/tempname
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@@ -1,5 +1,5 @@
Description:
gen_tempname() function: create a private temporary file or directory.
gen_tempname, gen_tempname_len: create a private temporary file or directory.
Files:
lib/tempname.c
@@ -9,6 +9,8 @@ m4/tempname.m4
Depends-on:
extensions
gettimeofday
randint
stdbool
stdint
sys_stat
sys_time