From 42158472a5e6854888a16aa2e0216040ec2eae36 Mon Sep 17 00:00:00 2001
From: Guillem Jover <guillem@debian.org>
Date: Sat, 13 Apr 2024 22:51:39 +0200
Subject: [PATCH] dpkg-realpath: Rewrite in C

This should make the code more robust against system issues on missing
shell interpreters or realpath and readlink commands.
---
 po/POTFILES.in       |   2 +
 src/Makefile.am      |   7 +-
 src/dpkg-realpath.sh | 179 -------------------------------------
 src/realpath/main.c  | 242 +++++++++++++++++++++++++++++++++++++++++++++++++++
 t/shellcheck.t       |   1 -
 5 files changed, 249 insertions(+), 182 deletions(-)
 delete mode 100755 src/dpkg-realpath.sh
 create mode 100644 src/realpath/main.c

diff --git a/po/POTFILES.in b/po/POTFILES.in
index a2386011a..34dea53f4 100644
--- a/po/POTFILES.in
+++ b/po/POTFILES.in
@@ -76,6 +76,8 @@ lib/dpkg/version.c
 src/common/force.c
 src/common/selinux.c
 
+src/realpath/main.c
+
 src/deb/build.c
 src/deb/extract.c
 src/deb/info.c
diff --git a/src/Makefile.am b/src/Makefile.am
index 6d0f2f24a..abb1d96cf 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -27,6 +27,7 @@ bin_PROGRAMS = \
 	dpkg-deb \
 	dpkg-divert \
 	dpkg-query \
+	dpkg-realpath \
 	dpkg-split \
 	dpkg-statoverride \
 	dpkg-trigger \
@@ -34,7 +35,6 @@ bin_PROGRAMS = \
 
 bin_SCRIPTS = \
 	dpkg-maintscript-helper \
-	dpkg-realpath \
 	# EOL
 
 pkglibexec_SCRIPTS = \
@@ -46,7 +46,6 @@ EXTRA_DIST += \
 	dpkg-db-backup.sh \
 	dpkg-db-keeper.sh \
 	dpkg-maintscript-helper.sh \
-	dpkg-realpath.sh \
 	# EOL
 
 CLEANFILES += \
@@ -107,6 +106,10 @@ dpkg_query_SOURCES = \
 	query/main.c \
 	# EOL
 
+dpkg_realpath_SOURCES = \
+	realpath/main.c \
+	# EOL
+
 dpkg_split_SOURCES = \
 	split/dpkg-split.h \
 	split/info.c \
diff --git a/src/dpkg-realpath.sh b/src/dpkg-realpath.sh
deleted file mode 100755
index 84438b49e..000000000
--- a/src/dpkg-realpath.sh
+++ /dev/null
@@ -1,179 +0,0 @@
-#!/bin/sh
-#
-# Copyright © 2020 Helmut Grohne <helmut@subdivi.de>
-# Copyright © 2020 Guillem Jover <guillem@debian.org>
-#
-# 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; either version 2 of the License, or
-# (at your option) any later version.
-#
-# 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.
-#
-# You should have received a copy of the GNU General Public License
-# along with this program.  If not, see <https://www.gnu.org/licenses/>.
-
-set -e
-
-PROGNAME=$(basename "$0")
-version="unknown"
-EOL="\n"
-
-PKGDATADIR_DEFAULT=src
-PKGDATADIR="${DPKG_DATADIR:-$PKGDATADIR_DEFAULT}"
-
-# shellcheck source=src/sh/dpkg-error.sh
-. "$PKGDATADIR/sh/dpkg-error.sh"
-
-show_version()
-{
-  cat <<END
-Debian $PROGNAME version $version.
-
-This is free software; see the GNU General Public License version 2 or
-later for copying conditions. There is NO warranty.
-END
-}
-
-show_usage()
-{
-  cat <<END
-Usage: $PROGNAME [<option>...] <pathname>
-
-Options:
-  -z, --zero                   end output line with NUL, not newline.
-      --instdir <directory>    set the root directory.
-      --root <directory>       set the root directory.
-      --version                show the version.
-  -?, --help                   show this help message.
-END
-}
-
-canonicalize() {
-  local src="$1"
-  local root="$DPKG_ROOT"
-  local loop=0
-  local result="$root"
-  local dst
-
-  # Check whether the path is relative and make it absolute otherwise.
-  if [ "$src" = "${src#/}" ]; then
-    src="$(pwd)/$src"
-    src="${src#"$root"}"
-  fi
-
-  # Remove prefixed slashes.
-  while [ "$src" != "${src#/}" ]; do
-     src=${src#/}
-  done
-  while [ -n "$src" ]; do
-    # Get the first directory component.
-    prefix=${src%%/*}
-    # Remove the first directory component from src.
-    src=${src#"$prefix"}
-    # Remove prefixed slashes.
-    while [ "$src" != "${src#/}" ]; do
-      src=${src#/}
-    done
-    # Resolve the first directory component.
-    if [ "$prefix" = . ]; then
-      # Ignore, stay at the same directory.
-      :
-    elif [ "$prefix" = .. ]; then
-      # Go up one directory.
-      result=${result%/*}
-      if [ -n "$root" ] && [ "${result#"$root"}" = "$result" ]; then
-        result="$root"
-      fi
-    elif [ -h "$result/$prefix" ]; then
-      loop=$((loop + 1))
-      if [ "$loop" -gt 25 ]; then
-        error "too many levels of symbolic links"
-      fi
-      # Resolve the symlink within $result.
-      dst=$(readlink "$result/$prefix")
-      case "$dst" in
-      /*)
-        # Absolute pathname, reset result back to $root.
-        result=$root
-        src="$dst${src:+/$src}"
-        # Remove prefixed slashes.
-        while [ "$src" != "${src#/}" ]; do
-          src=${src#/}
-        done
-        ;;
-      *)
-        # Relative pathname.
-        src="$dst${src:+/$src}"
-        ;;
-      esac
-    else
-      # Otherwise append the prefix.
-      result="$result/$prefix"
-    fi
-  done
-  # We are done, print the resolved pathname, w/o $root.
-  result="${result#"$root"}"
-  printf "%s$EOL" "${result:-/}"
-}
-
-setup_colors
-
-DPKG_ROOT="${DPKG_ROOT:-}"
-export DPKG_ROOT
-
-while [ $# -ne 0 ]; do
-  case "$1" in
-  -z|--zero)
-    EOL="\0"
-    ;;
-  --instdir|--root)
-    shift
-    DPKG_ROOT=$1
-    ;;
-  --instdir=*)
-    DPKG_ROOT="${1#--instdir=}"
-    ;;
-  --root=*)
-    DPKG_ROOT="${1#--root=}"
-    ;;
-  --version)
-    show_version
-    exit 0
-    ;;
-  --help|-\?)
-    show_usage
-    exit 0
-    ;;
-  --)
-    shift
-    pathname="$1"
-    ;;
-  -*)
-    badusage "unknown option: $1"
-    ;;
-  *)
-    pathname="$1"
-    ;;
-  esac
-  shift
-done
-
-# Normalize root directory.
-DPKG_ROOT="${DPKG_ROOT:+$(realpath "$DPKG_ROOT")}"
-# Remove default root dir.
-if [ "$DPKG_ROOT" = "/" ]; then
-  DPKG_ROOT=""
-fi
-
-[ -n "$pathname" ] || badusage "missing pathname"
-if [ "${pathname#"$DPKG_ROOT"}" != "$pathname" ]; then
-  error "link '$pathname' includes root prefix '$DPKG_ROOT'"
-fi
-
-canonicalize "$pathname"
-
-exit 0
diff --git a/src/realpath/main.c b/src/realpath/main.c
new file mode 100644
index 000000000..387294a61
--- /dev/null
+++ b/src/realpath/main.c
@@ -0,0 +1,242 @@
+/*
+ * dpkg-realpath - print the resolved pathname with DPKG_ROOT support
+ *
+ * Copyright © 2020 Helmut Grohne <helmut@subdivi.de>
+ * Copyright © 2020-2024 Guillem Jover <guillem@debian.org>
+ *
+ * This 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; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This 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.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <config.h>
+#include <compat.h>
+
+#include <sys/types.h>
+#include <sys/stat.h>
+
+#include <errno.h>
+#if HAVE_LOCALE_H
+#include <locale.h>
+#endif
+#include <string.h>
+#include <unistd.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <stdio.h>
+
+#include <dpkg/i18n.h>
+#include <dpkg/dpkg.h>
+#include <dpkg/dpkg-db.h>
+#include <dpkg/debug.h>
+#include <dpkg/string.h>
+#include <dpkg/db-fsys.h>
+#include <dpkg/options.h>
+
+static const char printforhelp[] = N_(
+"Use --help for help about this utility.");
+
+static void DPKG_ATTR_NORET
+printversion(const struct cmdinfo *cip, const char *value)
+{
+	printf(_("Debian %s version %s.\n"), dpkg_get_progname(),
+	       PACKAGE_RELEASE);
+
+	printf(_(
+"This is free software; see the GNU General Public License version 2 or\n"
+"later for copying conditions. There is NO warranty.\n"));
+
+	m_output(stdout, _("<standard output>"));
+
+	exit(0);
+}
+
+static void DPKG_ATTR_NORET
+usage(const struct cmdinfo *cip, const char *value)
+{
+	printf(_(
+"Usage: %s [<option>...] <pathname>\n"
+"\n"), dpkg_get_progname());
+
+	printf(_(
+"Options:\n"
+"  -z, --zero                   end output line with NUL, not newline.\n"
+"      --instdir <directory>    set the root directory.\n"
+"      --root <directory>       set the root directory.\n"
+"      --version                show the version.\n"
+"      --help                   show this help message.\n"
+"\n"));
+
+	m_output(stdout, _("<standard output>"));
+
+	exit(0);
+}
+
+static int opt_eol = '\n';
+
+static char *
+realpath_relative_to(const char *pathname, const char *rootdir)
+{
+	struct varbuf root = VARBUF_INIT;
+	struct varbuf src = VARBUF_INIT;
+	struct varbuf dst = VARBUF_INIT;
+	struct varbuf slink = VARBUF_INIT;
+	struct varbuf result = VARBUF_INIT;
+	struct varbuf prefix = VARBUF_INIT;
+	int loop = 0;
+
+	varbuf_set_str(&root, rootdir);
+	varbuf_set_str(&src, pathname);
+	varbuf_set_str(&result, rootdir);
+
+	/* Check whether the path is relative, make it absolute otherwise. */
+	if (src.buf[0] != '/') {
+		struct varbuf abs_src = VARBUF_INIT;
+
+		file_getcwd(&abs_src);
+		varbuf_add_char(&abs_src, '/');
+		varbuf_add_varbuf(&abs_src, &src);
+
+		varbuf_set_varbuf(&src, &abs_src);
+		varbuf_destroy(&abs_src);
+
+		varbuf_trim_varbuf_prefix(&src, &root);
+	}
+
+	/* Remove prefixed slashes. */
+	varbuf_trim_char_prefix(&src, '/');
+
+	while (src.used) {
+		struct stat st;
+		const char *slash;
+
+		/* Get the first directory component. */
+		varbuf_set_varbuf(&prefix, &src);
+		slash = strchrnul(prefix.buf, '/');
+		varbuf_trunc(&prefix, slash - prefix.buf);
+
+		/* Remove the first directory component from src. */
+		varbuf_trim_varbuf_prefix(&src, &prefix);
+
+		/* Remove prefixed slashes. */
+		varbuf_trim_char_prefix(&src, '/');
+
+		varbuf_set_varbuf(&slink, &result);
+		varbuf_add_char(&slink, '/');
+		varbuf_add_varbuf(&slink, &prefix);
+
+		/* Resolve the first directory component. */
+		if (strcmp(prefix.buf, ".") == 0) {
+			/* Ignore, stay at the same directory. */
+		} else if (strcmp(prefix.buf, "..") == 0) {
+			/* Go up one directory. */
+			slash = strrchr(result.buf, '/');
+			if (slash != NULL)
+				varbuf_trunc(&result, slash - result.buf);
+
+			if (root.used && !varbuf_has_prefix(&result, &root))
+				varbuf_set_varbuf(&result, &root);
+		} else if (lstat(slink.buf, &st) == 0 && S_ISLNK(st.st_mode)) {
+			ssize_t linksize;
+
+			loop++;
+			if (loop > 25)
+				ohshit(_("too many levels of symbolic links"));
+
+			/* Resolve the symlink within result. */
+			linksize = file_readlink(slink.buf, &dst, st.st_size);
+			if (linksize < 0)
+				ohshite(_("cannot read link '%s'"), slink.buf);
+			else if ((off_t)linksize != st.st_size)
+				ohshit(_("symbolic link '%s' size has changed from %jd to %zd"),
+				       slink.buf, (intmax_t)st.st_size, linksize);
+
+			if (dst.buf[0] == '/') {
+				/* Absolute pathname, reset result back to
+				 * root. */
+				varbuf_set_varbuf(&result, &root);
+
+				if (src.used) {
+					varbuf_add_char(&dst, '/');
+					varbuf_add_varbuf(&dst, &src);
+				}
+				varbuf_set_varbuf(&src, &dst);
+
+				/* Remove prefixed slashes. */
+				varbuf_trim_char_prefix(&src, '/');
+			} else {
+				/* Relative pathname. */
+				if (src.used) {
+					varbuf_add_char(&dst, '/');
+					varbuf_add_varbuf(&dst, &src);
+				}
+				varbuf_set_varbuf(&src, &dst);
+			}
+		} else {
+			/* Otherwise append the prefix. */
+			varbuf_add_char(&result, '/');
+			varbuf_add_varbuf(&result, &prefix);
+		}
+	}
+
+	/* We are done, return the resolved pathname, w/o root. */
+	varbuf_trim_varbuf_prefix(&result, &root);
+
+	varbuf_destroy(&root);
+	varbuf_destroy(&src);
+	varbuf_destroy(&dst);
+	varbuf_destroy(&slink);
+	varbuf_destroy(&prefix);
+
+	return varbuf_detach(&result);
+}
+
+static const struct cmdinfo cmdinfos[] = {
+	{ "zero",       'z', 0,  &opt_eol,     NULL,      NULL,         '\0' },
+	{ "instdir",    0,   1,  NULL,         NULL,      set_instdir,  0 },
+	{ "root",       0,   1,  NULL,         NULL,      set_instdir,  0 },
+	{ "version",    0,   0,  NULL,         NULL,      printversion  },
+	{ "help",       '?', 0,  NULL,         NULL,      usage         },
+	{  NULL,        0                                               }
+};
+
+int
+main(int argc, const char *const *argv)
+{
+	const char *instdir;
+	const char *pathname;
+	char *real_pathname;
+
+	dpkg_locales_init(PACKAGE);
+	dpkg_program_init("dpkg-realpath");
+	dpkg_options_parse(&argv, cmdinfos, printforhelp);
+
+	debug(dbg_general, "root=%s admindir=%s", dpkg_fsys_get_dir(), dpkg_db_get_dir());
+
+	pathname = argv[0];
+	if (pathname == NULL)
+		badusage(_("need a pathname argument"));
+
+	instdir = dpkg_fsys_get_dir();
+	if (strlen(instdir) && strncmp(pathname, instdir, strlen(instdir)) == 0)
+		badusage(_("link '%s' includes root prefix '%s'"),
+		         pathname, instdir);
+
+	real_pathname = realpath_relative_to(pathname, instdir);
+	printf("%s%c", real_pathname, opt_eol);
+	free(real_pathname);
+
+	dpkg_program_done();
+	dpkg_locales_done();
+
+	return 0;
+}
diff --git a/t/shellcheck.t b/t/shellcheck.t
index 12858ecd3..046bbb3eb 100644
--- a/t/shellcheck.t
+++ b/t/shellcheck.t
@@ -42,7 +42,6 @@ my @files = qw(
     src/dpkg-db-backup.sh
     src/dpkg-db-keeper.sh
     src/dpkg-maintscript-helper.sh
-    src/dpkg-realpath.sh
 );
 my @shellcheck_opts = (
     '--external-sources', # Allow checking external source files.
-- 
2.11.4.GIT