3 files changed, 91 insertions, 31 deletions

diff --git a/include/libbb.h b/include/libbb.h
index b72576f28..296417dae 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -578,7 +578,7 @@ DIR *xopendir(const char *path) FAST_FUNC;
 DIR *warn_opendir(const char *path) FAST_FUNC;
 
 char *xmalloc_realpath(const char *path) FAST_FUNC RETURNS_MALLOC;
-char *xmalloc_realpath_coreutils(const char *path) FAST_FUNC RETURNS_MALLOC;
+char *xmalloc_realpath_coreutils(char *path) FAST_FUNC RETURNS_MALLOC;
 char *xmalloc_readlink(const char *path) FAST_FUNC RETURNS_MALLOC;
 char *xmalloc_readlink_or_warn(const char *path) FAST_FUNC RETURNS_MALLOC;
 /* !RETURNS_MALLOC: it's a realloc-like function */
diff --git a/libbb/xreadlink.c b/libbb/xreadlink.c
index a18dd0748..2682f6975 100644
--- a/libbb/xreadlink.c
+++ b/libbb/xreadlink.c
@@ -123,7 +123,7 @@ char* FAST_FUNC xmalloc_realpath(const char *path)
 #endif
 }
 
-char* FAST_FUNC xmalloc_realpath_coreutils(const char *path)
+char* FAST_FUNC xmalloc_realpath_coreutils(char *path)
 {
         char *buf;
 
@@ -137,32 +137,19 @@ char* FAST_FUNC xmalloc_realpath_coreutils(const char *path)
          * (the directory must exist).
          */
         if (!buf && errno == ENOENT) {
-                char *last_slash = strrchr(path, '/');
-                if (last_slash) {
-                        *last_slash++ = '\0';
-                        buf = xmalloc_realpath(path);
-                        if (buf) {
-                                unsigned len = strlen(buf);
-                                buf = xrealloc(buf, len + strlen(last_slash) + 2);
-                                buf[len++] = '/';
-                                strcpy(buf + len, last_slash);
-                        }
-                } else {
-                        char *target = xmalloc_readlink(path);
-                        if (target) {
-                                char *cwd;
-                                if (target[0] == '/') {
-                                        /*
-                                         * $ ln -s /bin/qwe symlink  # note: /bin is a link to /usr/bin
-                                         * $ readlink -f symlink
-                                         * /usr/bin/qwe/target_does_not_exist
-                                         * $ realpath symlink
-                                         * /usr/bin/qwe/target_does_not_exist
-                                         */
-                                        buf = xmalloc_realpath_coreutils(target);
-                                        free(target);
-                                        return buf;
-                                }
+                char *target, c, *last_slash;
+                size_t i;
+
+                target = xmalloc_readlink(path);
+                if (target) {
+                        /*
+                         * $ ln -s /bin/qwe symlink  # note: /bin is a link to /usr/bin
+                         * $ readlink -f symlink
+                         * /usr/bin/qwe
+                         * $ realpath symlink
+                         * /usr/bin/qwe
+                         */
+                        if (target[0] != '/') {
                                 /*
                                  * $ ln -s target_does_not_exist symlink
                                  * $ readlink -f symlink
@@ -170,13 +157,41 @@ char* FAST_FUNC xmalloc_realpath_coreutils(const char *path)
                                  * $ realpath symlink
                                  * /CURDIR/target_does_not_exist
                                  */
-                                cwd = xrealloc_getcwd_or_warn(NULL);
-                                buf = concat_path_file(cwd, target);
+                                char *cwd = xrealloc_getcwd_or_warn(NULL);
+                                char *tmp = concat_path_file(cwd, target);
                                 free(cwd);
                                 free(target);
-                                return buf;
+                                target = tmp;
+                        }
+                        buf = xmalloc_realpath_coreutils(target);
+                        free(target);
+                        return buf;
+                }
+
+                /* ignore leading and trailing slashes */
+                while (path[0] == '/' && path[1] == '/')
+                        ++path;
+                i = strlen(path) - 1;
+                while (i > 0 && path[i] == '/')
+                        i--;
+                c = path[i + 1];
+                path[i + 1] = '\0';
+
+                last_slash = strrchr(path, '/');
+                if (last_slash == path)
+                        buf = xstrdup(path);
+                else if (last_slash) {
+                        *last_slash = '\0';
+                        buf = xmalloc_realpath(path);
+                        *last_slash++ = '/';
+                        if (buf) {
+                                unsigned len = strlen(buf);
+                                buf = xrealloc(buf, len + strlen(last_slash) + 2);
+                                buf[len++] = '/';
+                                strcpy(buf + len, last_slash);
                         }
                 }
+                path[i + 1] = c;
         }
 
         return buf;
diff --git a/testsuite/realpath.tests b/testsuite/realpath.tests
new file mode 100755
index 000000000..0e68e0279
--- /dev/null
+++ b/testsuite/realpath.tests
@@ -0,0 +1,45 @@
+#!/bin/sh
+
+# Realpath tests.
+# Copyright 2006 by Natanael Copa <n@tanael.org>
+# Copyright 2021 by Ron Yorston <rmy@pobox.com>
+# Licensed under GPLv2, see file LICENSE in this source tree.
+
+. ./testing.sh
+
+unset LC_ALL
+unset LC_MESSAGES
+unset LANG
+unset LANGUAGE
+
+TESTDIR=realpath_testdir
+TESTLINK1="link1"
+TESTLINK2="link2"
+
+# create the dir and test files
+mkdir -p "./$TESTDIR"
+ln -s "./$TESTDIR/not_file" "./$TESTLINK1"
+ln -s "./$TESTDIR/not_file/not_dir" "./$TESTLINK2"
+
+# shell's $PWD may leave symlinks unresolved.
+# "pwd" may be a built-in and have the same problem.
+# External pwd _can't_ have that problem (current dir on Unix is physical).
+pwd=`which pwd`
+pwd=`$pwd`
+testing "realpath on non-existent absolute path 1" "realpath /not_file" "/not_file\n" "" ""
+testing "realpath on non-existent absolute path 2" "realpath /not_file/" "/not_file\n" "" ""
+testing "realpath on non-existent absolute path 3" "realpath //not_file" "/not_file\n" "" ""
+testing "realpath on non-existent absolute path 4" "realpath /not_dir/not_file 2>&1" "realpath: /not_dir/not_file: No such file or directory\n" "" ""
+
+testing "realpath on non-existent local file 1" "realpath $TESTDIR/not_file" "$pwd/$TESTDIR/not_file\n" "" ""
+testing "realpath on non-existent local file 2" "realpath $TESTDIR/not_dir/not_file 2>&1" "realpath: $TESTDIR/not_dir/not_file: No such file or directory\n" "" ""
+
+testing "realpath on link to non-existent file 1" "realpath $TESTLINK1" "$pwd/$TESTDIR/not_file\n" "" ""
+testing "realpath on link to non-existent file 2" "realpath $TESTLINK2 2>&1" "realpath: $TESTLINK2: No such file or directory\n" "" ""
+testing "realpath on link to non-existent file 3" "realpath ./$TESTLINK1" "$pwd/$TESTDIR/not_file\n" "" ""
+testing "realpath on link to non-existent file 4" "realpath ./$TESTLINK2 2>&1" "realpath: ./$TESTLINK2: No such file or directory\n" "" ""
+
+# clean up
+rm -r "$TESTLINK1" "$TESTLINK2" "$TESTDIR"
+
+exit $((FAILCOUNT <= 255 ? FAILCOUNT : 255))