[PATCH 05/13] lib/crypt: Add helpers for operating on /etc/shadow

[Stewart Smith]

Samuel Mendoza-Jonas <sam at mendozajonas.com> writes:
> Provides helper functions for reading, writing, and checking against
> /etc/shadow. The main use case if for authenticating clients against the
> "system" password, which is set as the root password.
>
> Signed-off-by: Samuel Mendoza-Jonas <sam at mendozajonas.com>
> ---
>  configure.ac      |  22 ++++++++
>  lib/Makefile.am   |   9 ++++
>  lib/crypt/crypt.c | 126 ++++++++++++++++++++++++++++++++++++++++++++++
>  lib/crypt/crypt.h |  49 ++++++++++++++++++
>  4 files changed, 206 insertions(+)
>  create mode 100644 lib/crypt/crypt.c
>  create mode 100644 lib/crypt/crypt.h
>
> diff --git a/configure.ac b/configure.ac
> index 2bf6e6f6..4151b002 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -76,6 +76,27 @@ AC_CHECK_LIB([devmapper], [dm_task_create],
>  	[AC_MSG_FAILURE([The libdevmapper development library is required by petitboot.  Try installing the package libdevmapper-dev or device-mapper-devel.])]
>  )
>
> +AC_ARG_ENABLE(
> +	[crypt],
> +	[AS_HELP_STRING(
> +		[--enable-crypt],
> +		[Include crypt support to enable password use [default=no]]
> +	)],
> +	[],
> +	[enable_crypt=no]
> +)
> +AM_CONDITIONAL([ENABLE_CRYPT], [test "x$enable_crypt" = "xyes"])
> +AS_IF([test "x$enable_crypt" = "xyes"],
> +      [AC_DEFINE(CRYPT_SUPPORT, 1, [Enable crypt/password support])],
> +      []
> +)
> +AS_IF([test "x$enable_crypt" = "xyes"],
> +	AC_CHECK_LIB([crypt], [crypt],
> +		[CRYPT_LIBS=-lcrypt],
> +		[AC_MSG_FAILURE([shadow/crypt libs required])]
> +	)
> +)
> +
>  AC_ARG_WITH([fdt],
>  	AS_HELP_STRING([--without-fdt],
>  		[Build without libfdt (default: no)]))
> @@ -455,6 +476,7 @@ AS_IF(
>   
>  AC_SUBST([UDEV_LIBS])
>  AC_SUBST([DEVMAPPER_LIBS])
> +AC_SUBST([CRYPT_LIBS])
>  AC_SUBST([FDT_LIBS])
>  AC_SUBST([LIBFLASH_LIBS])
>  AC_SUBST([LIBTOOL_DEPS])
> diff --git a/lib/Makefile.am b/lib/Makefile.am
> index 016a14dd..69a66c37 100644
> --- a/lib/Makefile.am
> +++ b/lib/Makefile.am
> @@ -35,6 +35,7 @@ lib_libpbcore_la_CFLAGS = \
>
>  lib_libpbcore_la_SOURCES = \
>  	lib/ccan/endian/endian.h \
> +	lib/crypt/crypt.h \
>  	lib/file/file.h \
>  	lib/file/file.c \
>  	lib/fold/fold.h \
> @@ -93,3 +94,11 @@ lib_libpbcore_la_SOURCES += \
>  	lib/security/none.c
>  endif
>  endif
> +
> +if ENABLE_CRYPT
> +lib_libpbcore_la_SOURCES += \
> +	lib/crypt/crypt.c
> +
> +lib_libpbcore_la_LDFLAGS += \
> +	$(CRYPT_LIBS)
> +endif
> diff --git a/lib/crypt/crypt.c b/lib/crypt/crypt.c
> new file mode 100644
> index 00000000..dcaf3afe
> --- /dev/null
> +++ b/lib/crypt/crypt.c
> @@ -0,0 +1,126 @@
> +/*
> + *  Copyright (C) 2018 IBM Corporation
> + *
> + *  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
> + *  the Free Software Foundation; version 2 of the License.
> + *
> + *  This program 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 General Public License for more details.
> + *
> + */
> +#include <string.h>
> +#include <errno.h>
> +#include <stdlib.h>
> +#include <shadow.h>
> +#include <crypt.h>
> +#include <errno.h>
> +
> +#include <talloc/talloc.h>
> +#include <log/log.h>
> +
> +#include "crypt.h"
> +
> +int crypt_set_password_hash(void *ctx, const char *hash)
> +{
> +	struct spwd *shadow;
> +	FILE *fp;
> +	int rc;
> +
> +	shadow = getspnam("root");
> +	if (!shadow) {
> +		pb_log("Could not find root shadow\n");
> +		return -1;
> +	}
> +
> +	shadow->sp_pwdp = talloc_strdup(ctx, hash);
> +	if (!shadow->sp_pwdp) {
> +		pb_log("Could not assign password\n");
> +		return -1;
> +	}
> +
> +	lckpwdf();
> +
> +	fp = fopen("/etc/shadow", "w+");
> +	if (!fp) {
> +		pb_log("Could not open shadow file\n");
> +		rc = -1;
> +		goto out;
> +	}
> +
> +	rc = putspent(shadow, fp);
> +	if (rc)
> +		pb_log("Failed to set password hash\n");
> +
> +	talloc_free(shadow->sp_pwdp);
> +out:
> +	fclose(fp);

I don't think fclose() can take NULL, which would be hit by a failure in
the fopen() path above.

*technically* fclose() can also file with EIO,ENOSPC etc (everything
close(2), write(2), or fflush(3) can fail with) so *possibly* worthwhile
checking for it here, at least so we have well defined behaviour?


-- 
Stewart Smith
OPAL Architect, IBM.