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841785bad1
This is a major rewrite of the description of 'crypt', 'getentropy', and 'getrandom'. A few highlights of the content changes: - Throughout the manual, public headers, and user-visible messages, I replaced the term "password" with "passphrase", the term "password database" with "user database", and the term "encrypt(ion)" with "(one-way) hashing" whenever it was applied to passphrases. I didn't bother making this change in internal code or tests. The use of the term "password" in ruserpass.c survives, because that refers to a keyword in netrc files, but it is adjusted to make this clearer. There is a note in crypt.texi explaining that they were traditionally called passwords but single words are not good enough anymore, and a note in users.texi explaining that actual passphrase hashes are found in a "shadow" database nowadays. - There is a new short introduction to the "Cryptographic Functions" section, explaining how we do not intend to be a general-purpose cryptography library, and cautioning that there _are_, or have been, legal restrictions on the use of cryptography in many countries, without getting into any kind of detail that we can't promise to keep up to date. - I added more detail about what a "one-way function" is, and why they are used to obscure passphrases for storage. I removed the paragraph saying that systems not connected to a network need no user authentication, because that's a pretty rare situation nowadays. (It still says "sometimes it is necessary" to authenticate the user, though.) - I added documentation for all of the hash functions that glibc actually supports, but not for the additional hash functions supported by libxcrypt. If we're going to keep this manual section around after the transition is more advanced, it would probably make sense to add them then. - There is much more detailed discussion of how to generate a salt, and the failure behavior for crypt is documented. (Returning an invalid hash on failure is what libxcrypt does; Solar Designer's notes say that this was done "for compatibility with old programs that assume crypt can never fail".) - As far as I can tell, the header 'crypt.h' is entirely a GNU invention, and never existed on any other Unix lineage. The function 'crypt', however, was in Issue 1 of the SVID and is now in the XSI component of POSIX. I tried to make all of the @standards annotations consistent with this, but I'm not sure I got them perfectly right. - The genpass.c example has been improved to use getentropy instead of the current time to generate the salt, and to use a SHA-256 hash instead of MD5. It uses more random bytes than is strictly necessary because I didn't want to complicate the code with proper base64 encoding. - The testpass.c example has three hardwired hashes now, to demonstrate that different one-way functions produce different hashes for the same input. It also demonstrates how DES hashing only pays attention to the first eight characters of the input. - There is new text explaining in more detail how a CSPRNG differs from a regular random number generator, and how getentropy/getrandom are not exactly a CSPRNG. I tried not to make specific falsifiable claims here. I also tried to make the blocking/cancellation/error behavior of both getentropy and getrandom clearer.
190 lines
6.0 KiB
C
190 lines
6.0 KiB
C
/* Copyright (C) 1991-2018 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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/*
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* POSIX Standard: 9.2.2 User Database Access <pwd.h>
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*/
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#ifndef _PWD_H
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#define _PWD_H 1
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#include <features.h>
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__BEGIN_DECLS
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#include <bits/types.h>
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#define __need_size_t
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#include <stddef.h>
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#if defined __USE_XOPEN || defined __USE_XOPEN2K
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/* The Single Unix specification says that some more types are
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available here. */
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# ifndef __gid_t_defined
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typedef __gid_t gid_t;
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# define __gid_t_defined
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# endif
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# ifndef __uid_t_defined
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typedef __uid_t uid_t;
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# define __uid_t_defined
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# endif
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#endif
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/* A record in the user database. */
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struct passwd
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{
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char *pw_name; /* Username. */
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char *pw_passwd; /* Hashed passphrase, if shadow database
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not in use (see shadow.h). */
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__uid_t pw_uid; /* User ID. */
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__gid_t pw_gid; /* Group ID. */
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char *pw_gecos; /* Real name. */
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char *pw_dir; /* Home directory. */
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char *pw_shell; /* Shell program. */
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};
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#ifdef __USE_MISC
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# include <bits/types/FILE.h>
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#endif
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#if defined __USE_MISC || defined __USE_XOPEN_EXTENDED
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/* Rewind the user database stream.
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This function is a possible cancellation point and therefore not
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marked with __THROW. */
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extern void setpwent (void);
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/* Close the user database stream.
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This function is a possible cancellation point and therefore not
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marked with __THROW. */
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extern void endpwent (void);
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/* Read an entry from the user database stream, opening it if necessary.
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This function is a possible cancellation point and therefore not
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marked with __THROW. */
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extern struct passwd *getpwent (void);
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#endif
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#ifdef __USE_MISC
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/* Read a user database entry from STREAM.
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This function is not part of POSIX and therefore no official
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cancellation point. But due to similarity with an POSIX interface
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or due to the implementation it is a cancellation point and
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therefore not marked with __THROW. */
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extern struct passwd *fgetpwent (FILE *__stream) __nonnull ((1));
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/* Write a given user database entry onto the given stream.
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This function is not part of POSIX and therefore no official
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cancellation point. But due to similarity with an POSIX interface
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or due to the implementation it is a cancellation point and
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therefore not marked with __THROW. */
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extern int putpwent (const struct passwd *__restrict __p,
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FILE *__restrict __f);
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#endif
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/* Retrieve the user database entry for the given user ID.
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This function is a possible cancellation point and therefore not
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marked with __THROW. */
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extern struct passwd *getpwuid (__uid_t __uid);
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/* Retrieve the user database entry for the given username.
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This function is a possible cancellation point and therefore not
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marked with __THROW. */
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extern struct passwd *getpwnam (const char *__name) __nonnull ((1));
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#ifdef __USE_POSIX
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# ifdef __USE_MISC
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/* Reasonable value for the buffer sized used in the reentrant
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functions below. But better use `sysconf'. */
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# define NSS_BUFLEN_PASSWD 1024
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# endif
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/* Reentrant versions of some of the functions above.
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PLEASE NOTE: the `getpwent_r' function is not (yet) standardized.
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The interface may change in later versions of this library. But
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the interface is designed following the principals used for the
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other reentrant functions so the chances are good this is what the
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POSIX people would choose. */
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# ifdef __USE_MISC
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/* This function is not part of POSIX and therefore no official
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cancellation point. But due to similarity with an POSIX interface
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or due to the implementation it is a cancellation point and
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therefore not marked with __THROW. */
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extern int getpwent_r (struct passwd *__restrict __resultbuf,
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char *__restrict __buffer, size_t __buflen,
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struct passwd **__restrict __result)
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__nonnull ((1, 2, 4));
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# endif
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extern int getpwuid_r (__uid_t __uid,
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struct passwd *__restrict __resultbuf,
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char *__restrict __buffer, size_t __buflen,
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struct passwd **__restrict __result)
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__nonnull ((2, 3, 5));
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extern int getpwnam_r (const char *__restrict __name,
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struct passwd *__restrict __resultbuf,
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char *__restrict __buffer, size_t __buflen,
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struct passwd **__restrict __result)
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__nonnull ((1, 2, 3, 5));
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# ifdef __USE_MISC
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/* Read a user database entry from STREAM. This function is not
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standardized and probably never will.
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This function is not part of POSIX and therefore no official
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cancellation point. But due to similarity with an POSIX interface
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or due to the implementation it is a cancellation point and
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therefore not marked with __THROW. */
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extern int fgetpwent_r (FILE *__restrict __stream,
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struct passwd *__restrict __resultbuf,
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char *__restrict __buffer, size_t __buflen,
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struct passwd **__restrict __result)
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__nonnull ((1, 2, 3, 5));
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# endif
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#endif /* POSIX or reentrant */
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#ifdef __USE_GNU
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/* Write a traditional /etc/passwd line, based on the user database
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entry for the given UID, to BUFFER; space for BUFFER must be
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allocated by the caller.
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This function is not part of POSIX and therefore no official
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cancellation point. But due to similarity with an POSIX interface
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or due to the implementation it is a cancellation point and
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therefore not marked with __THROW. */
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extern int getpw (__uid_t __uid, char *__buffer);
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#endif
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__END_DECLS
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#endif /* pwd.h */
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