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Diffstat (limited to 'lib/tempname.c')
| -rw-r--r-- | lib/tempname.c | 286 |
1 files changed, 286 insertions, 0 deletions
diff --git a/lib/tempname.c b/lib/tempname.c new file mode 100644 index 0000000..bf362db --- /dev/null +++ b/lib/tempname.c @@ -0,0 +1,286 @@ +/* Copyright (C) 1991-2023 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + <https://www.gnu.org/licenses/>. */ + +#if !_LIBC +# include <libc-config.h> +# include "tempname.h" +#endif + +#include <errno.h> + +#include <stdio.h> +#ifndef TMP_MAX +# define TMP_MAX 238328 +#endif +#ifndef __GT_FILE +# define __GT_FILE 0 +# define __GT_DIR 1 +# define __GT_NOCREATE 2 +#endif +#if !_LIBC && (GT_FILE != __GT_FILE || GT_DIR != __GT_DIR \ + || GT_NOCREATE != __GT_NOCREATE) +# error report this to bug-gnulib@gnu.org +#endif + +#include <stdlib.h> +#include <string.h> + +#include <fcntl.h> +#include <stdint.h> +#include <sys/random.h> +#include <sys/stat.h> +#include <time.h> + +#if _LIBC +# define struct_stat64 struct __stat64_t64 +#else +# define struct_stat64 struct stat +# define __gen_tempname gen_tempname +# define __mkdir mkdir +# define __open open +# define __lstat64_time64(file, buf) lstat (file, buf) +# define __getrandom getrandom +# define __clock_gettime64 clock_gettime +# define __timespec64 timespec +#endif + +/* Use getrandom if it works, falling back on a 64-bit linear + congruential generator that starts with Var's value + mixed in with a clock's low-order bits if available. */ +typedef uint_fast64_t random_value; +#define RANDOM_VALUE_MAX UINT_FAST64_MAX +#define BASE_62_DIGITS 10 /* 62**10 < UINT_FAST64_MAX */ +#define BASE_62_POWER (62LL * 62 * 62 * 62 * 62 * 62 * 62 * 62 * 62 * 62) + +/* Return the result of mixing the entropy from R and S. + Assume that R and S are not particularly random, + and that the result should look randomish to an untrained eye. */ + +static random_value +mix_random_values (random_value r, random_value s) +{ + /* As this code is used only when high-quality randomness is neither + available nor necessary, there is no need for fancier polynomials + such as those in the Linux kernel's 'random' driver. */ + return (2862933555777941757 * r + 3037000493) ^ s; +} + +/* Set *R to a random value. + Return true if *R is set to high-quality value taken from getrandom. + Otherwise return false, falling back to a low-quality *R that might + depend on S. + + This function returns false only when getrandom fails. + On GNU systems this should happen only early in the boot process, + when the fallback should be good enough for programs using tempname + because any attacker likely has root privileges already. */ + +static bool +random_bits (random_value *r, random_value s) +{ + /* Without GRND_NONBLOCK it can be blocked for minutes on some systems. */ + if (__getrandom (r, sizeof *r, GRND_NONBLOCK) == sizeof *r) + return true; + + /* If getrandom did not work, use ersatz entropy based on low-order + clock bits. On GNU systems getrandom should fail only + early in booting, when ersatz should be good enough. + Do not use ASLR-based entropy, as that would leak ASLR info into + the resulting file name which is typically public. + + Of course we are in a state of sin here. */ + + random_value v = s; + +#if _LIBC || (defined CLOCK_REALTIME && HAVE_CLOCK_GETTIME) + struct __timespec64 tv; + __clock_gettime64 (CLOCK_REALTIME, &tv); + v = mix_random_values (v, tv.tv_sec); + v = mix_random_values (v, tv.tv_nsec); +#endif + + *r = mix_random_values (v, clock ()); + return false; +} + +#if _LIBC +static int try_tempname_len (char *, int, void *, int (*) (char *, void *), + size_t); +#endif + +static int +try_file (char *tmpl, void *flags) +{ + int *openflags = flags; + return __open (tmpl, + (*openflags & ~O_ACCMODE) + | O_RDWR | O_CREAT | O_EXCL, S_IRUSR | S_IWUSR); +} + +static int +try_dir (char *tmpl, _GL_UNUSED void *flags) +{ + return __mkdir (tmpl, S_IRUSR | S_IWUSR | S_IXUSR); +} + +static int +try_nocreate (char *tmpl, _GL_UNUSED void *flags) +{ + struct_stat64 st; + + if (__lstat64_time64 (tmpl, &st) == 0 || errno == EOVERFLOW) + __set_errno (EEXIST); + return errno == ENOENT ? 0 : -1; +} + +/* 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 at least X_SUFFIX_LEN "X"s, + possibly with a suffix). + The name constructed does not exist at the time of the call to + this function. TMPL is overwritten with the result. + + KIND may be one of: + __GT_NOCREATE: simply verify that the name does not exist + at the time of the call. + __GT_FILE: create the file using open(O_CREAT|O_EXCL) + and return a read-write fd. The file is mode 0600. + __GT_DIR: create a directory, which will be mode 0700. + + */ +#ifdef _LIBC +static +#endif +int +gen_tempname_len (char *tmpl, int suffixlen, int flags, int kind, + size_t x_suffix_len) +{ + static int (*const tryfunc[]) (char *, void *) = + { + [__GT_FILE] = try_file, + [__GT_DIR] = try_dir, + [__GT_NOCREATE] = try_nocreate + }; + return try_tempname_len (tmpl, suffixlen, &flags, tryfunc[kind], + x_suffix_len); +} + +#ifdef _LIBC +static +#endif +int +try_tempname_len (char *tmpl, int suffixlen, void *args, + int (*tryfunc) (char *, void *), size_t x_suffix_len) +{ + size_t len; + char *XXXXXX; + unsigned int count; + int fd = -1; + int save_errno = errno; + + /* A lower bound on the number of temporary files to attempt to + generate. The maximum total number of temporary file names that + can exist for a given template is 62**6. It should never be + necessary to try all of these combinations. Instead if a reasonable + number of names is tried (we define reasonable as 62**3) fail to + give the system administrator the chance to remove the problems. + This value requires that X_SUFFIX_LEN be at least 3. */ +#define ATTEMPTS_MIN (62 * 62 * 62) + + /* The number of times to attempt to generate a temporary file. To + conform to POSIX, this must be no smaller than TMP_MAX. */ +#if ATTEMPTS_MIN < TMP_MAX + unsigned int attempts = TMP_MAX; +#else + unsigned int attempts = ATTEMPTS_MIN; +#endif + + /* A random variable. */ + random_value v = 0; + + /* A value derived from the random variable, and how many random + base-62 digits can currently be extracted from VDIGBUF. */ + random_value vdigbuf; + int vdigits = 0; + + /* Least biased value for V. If V is less than this, V can generate + BASE_62_DIGITS unbiased digits. Otherwise the digits are biased. */ + random_value const biased_min + = RANDOM_VALUE_MAX - RANDOM_VALUE_MAX % BASE_62_POWER; + + len = strlen (tmpl); + if (len < x_suffix_len + suffixlen + || strspn (&tmpl[len - x_suffix_len - suffixlen], "X") < x_suffix_len) + { + __set_errno (EINVAL); + return -1; + } + + /* This is where the Xs start. */ + XXXXXX = &tmpl[len - x_suffix_len - suffixlen]; + + for (count = 0; count < attempts; ++count) + { + for (size_t i = 0; i < x_suffix_len; i++) + { + if (vdigits == 0) + { + /* Worry about bias only if the bits are high quality. */ + while (random_bits (&v, v) && biased_min <= v) + continue; + + vdigbuf = v; + vdigits = BASE_62_DIGITS; + } + + XXXXXX[i] = letters[vdigbuf % 62]; + vdigbuf /= 62; + vdigits--; + } + + fd = tryfunc (tmpl, args); + if (fd >= 0) + { + __set_errno (save_errno); + return fd; + } + else if (errno != EEXIST) + return -1; + } + + /* We got out of the loop because we ran out of combinations to try. */ + __set_errno (EEXIST); + return -1; +} + +int +__gen_tempname (char *tmpl, int suffixlen, int flags, int kind) +{ + return gen_tempname_len (tmpl, suffixlen, flags, kind, 6); +} + +#if !_LIBC +int +try_tempname (char *tmpl, int suffixlen, void *args, + int (*tryfunc) (char *, void *)) +{ + return try_tempname_len (tmpl, suffixlen, args, tryfunc, 6); +} +#endif |