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Diffstat (limited to '')
| -rw-r--r-- | lib/tempname.c | 345 |
1 files changed, 345 insertions, 0 deletions
diff --git a/lib/tempname.c b/lib/tempname.c new file mode 100644 index 0000000..5fc5efe --- /dev/null +++ b/lib/tempname.c @@ -0,0 +1,345 @@ +/* Copyright (C) 1991-2022 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 <sys/types.h> +#include <assert.h> +#include <stdbool.h> + +#include <errno.h> + +#include <stdio.h> +#ifndef P_tmpdir +# define P_tmpdir "/tmp" +#endif +#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 <stddef.h> +#include <stdlib.h> +#include <string.h> + +#include <fcntl.h> +#include <stdalign.h> +#include <stdint.h> +#include <sys/random.h> +#include <sys/stat.h> +#include <time.h> + +#if _LIBC +# define struct_stat64 struct stat64 +# define __secure_getenv __libc_secure_getenv +#else +# define struct_stat64 struct stat +# define __gen_tempname gen_tempname +# define __mkdir mkdir +# define __open open +# define __lstat64(file, buf) lstat (file, buf) +# define __stat64(file, buf) stat (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) + +static random_value +random_bits (random_value var, bool use_getrandom) +{ + random_value r; + /* Without GRND_NONBLOCK it can be blocked for minutes on some systems. */ + if (use_getrandom && __getrandom (&r, sizeof r, GRND_NONBLOCK) == sizeof r) + return r; +#if _LIBC || (defined CLOCK_MONOTONIC && HAVE_CLOCK_GETTIME) + /* Add entropy if getrandom did not work. */ + struct __timespec64 tv; + __clock_gettime64 (CLOCK_MONOTONIC, &tv); + var ^= tv.tv_nsec; +#endif + return 2862933555777941757 * var + 3037000493; +} + +#if _LIBC +/* Return nonzero if DIR is an existent directory. */ +static int +direxists (const char *dir) +{ + struct_stat64 buf; + return __stat64 (dir, &buf) == 0 && S_ISDIR (buf.st_mode); +} + +/* Path search algorithm, for tmpnam, tmpfile, etc. If DIR is + non-null and exists, uses it; otherwise uses the first of $TMPDIR, + P_tmpdir, /tmp that exists. Copies into TMPL a template suitable + for use with mk[s]temp. Will fail (-1) if DIR is non-null and + doesn't exist, none of the searched dirs exists, or there's not + enough space in TMPL. */ +int +__path_search (char *tmpl, size_t tmpl_len, const char *dir, const char *pfx, + int try_tmpdir) +{ + const char *d; + size_t dlen, plen; + + if (!pfx || !pfx[0]) + { + pfx = "file"; + plen = 4; + } + else + { + plen = strlen (pfx); + if (plen > 5) + plen = 5; + } + + if (try_tmpdir) + { + d = __secure_getenv ("TMPDIR"); + if (d != NULL && direxists (d)) + dir = d; + else if (dir != NULL && direxists (dir)) + /* nothing */ ; + else + dir = NULL; + } + if (dir == NULL) + { + if (direxists (P_tmpdir)) + dir = P_tmpdir; + else if (strcmp (P_tmpdir, "/tmp") != 0 && direxists ("/tmp")) + dir = "/tmp"; + else + { + __set_errno (ENOENT); + return -1; + } + } + + dlen = strlen (dir); + while (dlen > 1 && dir[dlen - 1] == '/') + dlen--; /* remove trailing slashes */ + + /* check we have room for "${dir}/${pfx}XXXXXX\0" */ + if (tmpl_len < dlen + 1 + plen + 6 + 1) + { + __set_errno (EINVAL); + return -1; + } + + sprintf (tmpl, "%.*s/%.*sXXXXXX", (int) dlen, dir, (int) plen, pfx); + return 0; +} +#endif /* _LIBC */ + +#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 (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. + + We use a clever algorithm to get hard-to-predict names. */ +#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. The initial value is used only the for fallback path + on 'random_bits' on 'getrandom' failure. Its initial value tries to use + some entropy from the ASLR and ignore possible bits from the stack + alignment. */ + random_value v = ((uintptr_t) &v) / alignof (max_align_t); + + /* How many random base-62 digits can currently be extracted from V. */ + int vdigits = 0; + + /* Whether to consume entropy when acquiring random bits. On the + first try it's worth the entropy cost with __GT_NOCREATE, which + is inherently insecure and can use the entropy to make it a bit + less secure. On the (rare) second and later attempts it might + help against DoS attacks. */ + bool use_getrandom = tryfunc == try_nocreate; + + /* Least unfair value for V. If V is less than this, V can generate + BASE_62_DIGITS digits fairly. Otherwise it might be biased. */ + random_value const unfair_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) + { + do + { + v = random_bits (v, use_getrandom); + use_getrandom = true; + } + while (unfair_min <= v); + + vdigits = BASE_62_DIGITS; + } + + XXXXXX[i] = letters[v % 62]; + v /= 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 |