Add a GNU-compatible version of basename(3).

Unlike POSIX basename(3), the GNU variant does not modify its argument.
Note that basename of a path ending in "/" returns an empty string.

MANIFEST

@@ -158,6 +158,7 @@ lib/util/aix.c
 lib/util/arc4random.c
 lib/util/arc4random_buf.c
 lib/util/arc4random_uniform.c
+lib/util/basename.c
 lib/util/cfmakeraw.c
 lib/util/chacha_private.h
 lib/util/closefrom.c

include/sudo_util.h

@@ -188,6 +188,10 @@ sudo_dso_public int aix_setauthdb_v1(char *user);
 sudo_dso_public int aix_setauthdb_v2(char *user, char *registry);
 #define aix_setauthdb(_a, _b) aix_setauthdb_v2((_a), (_b))
 
+/* basename.c */
+sudo_dso_public char *sudo_basename_v1(const char *filename);
+#define sudo_basename(_a) sudo_basename_v1(_a)
+
 /* gethostname.c */
 sudo_dso_public char *sudo_gethostname_v1(void);
 #define sudo_gethostname() sudo_gethostname_v1()

lib/util/Makefile.in

@@ -120,8 +120,8 @@ DEVEL = @DEVEL@
 
 SHELL = @SHELL@
 
-LTOBJS = @DIGEST@ event.lo fatal.lo key_val.lo gethostname.lo gettime.lo \
-	 getgrouplist.lo gidlist.lo json.lo lbuf.lo locking.lo \
+LTOBJS = basename.lo @DIGEST@ event.lo fatal.lo key_val.lo gethostname.lo \
+	 gettime.lo getgrouplist.lo gidlist.lo json.lo lbuf.lo locking.lo \
          logfac.lo logpri.lo mkdir_parents.lo parseln.lo progname.lo \
          roundup.lo secure_path.lo setgroups.lo strsplit.lo strtobool.lo \
          strtoid.lo strtomode.lo strtonum.lo sudo_conf.lo \
@@ -459,6 +459,14 @@ arc4random_uniform.i: $(srcdir)/arc4random_uniform.c $(incdir)/sudo_compat.h \
 	$(CC) -E -o $@ $(CPPFLAGS) $<
 arc4random_uniform.plog: arc4random_uniform.i
 	rm -f $@; pvs-studio --cfg $(PVS_CFG) --sourcetree-root $(top_srcdir) --skip-cl-exe yes --source-file $(srcdir)/arc4random_uniform.c --i-file $< --output-file $@
+basename.lo: $(srcdir)/basename.c $(incdir)/sudo_compat.h \
+             $(top_builddir)/config.h
+	$(LIBTOOL) $(LTFLAGS) --mode=compile $(CC) -c -o $@ $(CPPFLAGS) $(CFLAGS) $(ASAN_CFLAGS) $(PIE_CFLAGS) $(SSP_CFLAGS) $(srcdir)/basename.c
+basename.i: $(srcdir)/basename.c $(incdir)/sudo_compat.h \
+             $(top_builddir)/config.h
+	$(CC) -E -o $@ $(CPPFLAGS) $<
+basename.plog: basename.i
+	rm -f $@; pvs-studio --cfg $(PVS_CFG) --sourcetree-root $(top_srcdir) --skip-cl-exe yes --source-file $(srcdir)/basename.c --i-file $< --output-file $@
 cfmakeraw.lo: $(srcdir)/cfmakeraw.c $(incdir)/sudo_compat.h \
               $(top_builddir)/config.h
 	$(LIBTOOL) $(LTFLAGS) --mode=compile $(CC) -c -o $@ $(CPPFLAGS) $(CFLAGS) $(ASAN_CFLAGS) $(PIE_CFLAGS) $(SSP_CFLAGS) $(srcdir)/cfmakeraw.c

lib/util/basename.c

@@ -0,0 +1,52 @@
+/*
+ * SPDX-License-Identifier: ISC
+ *
+ * Copyright (c) 2021 Todd C. Miller <Todd.Miller@sudo.ws>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+/*
+ * This is an open source non-commercial project. Dear PVS-Studio, please check it.
+ * PVS-Studio Static Code Analyzer for C, C++ and C#: http://www.viva64.com
+ */
+
+#include <config.h>
+
+#include <errno.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <syslog.h>
+
+#include "sudo_compat.h"
+#include "sudo_util.h"
+
+/*
+ * GNU-compatible basename(3)
+ * Unlike the POSIX version, this version never modifies its argument
+ * and returns an empty string if filename ends in a slash.
+ */
+char *
+sudo_basename_v1(const char *filename)
+{
+    char *base;
+
+    if ((base = strrchr(filename, '/')) != NULL)
+	base++;
+    else
+	base = (char *)filename;
+
+    return base;
+}

lib/util/util.exp.in

@@ -1,5 +1,6 @@
 @COMPAT_EXP@initprogname
 initprogname2
+sudo_basename
 sudo_conf_askpass_path_v1
 sudo_conf_clear_paths_v1
 sudo_conf_debug_files_v1