findprog, relocatable-prog: Ignore directories during PATH search.

Reported by Frederick Eaton via Dmitry Goncharov in
<https://lists.gnu.org/archive/html/bug-gnulib/2020-03/msg00003.html>.

* lib/findprog.c (find_in_path): When the file found in a PATH element
is a directory, continue searching.
* modules/findprog (Depends-on): Add sys_stat, stat.
* modules/findprog-lgpl (Depends-on): Likewise.

* lib/progreloc.c (maybe_executable): When the file found in a PATH
element is a directory, continue searching.
* lib/relocwrapper.c: Update comments.
* modules/relocatable-prog-wrapper (Files): Add m4/largefile.m4.
(configure.ac-early): New section.

1 files changed, 24 insertions, 14 deletions

diff --git a/lib/findprog.c b/lib/findprog.c
index d0d41791e2..b562e9da6a 100644
--- a/lib/findprog.c
+++ b/lib/findprog.c
@@ -25,6 +25,9 @@
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
+#if !(defined _WIN32 || defined __CYGWIN__ || defined __EMX__ || defined __DJGPP__)
+# include <sys/stat.h>
+#endif
 
 /* Avoid collision between findprog.c and findprog-lgpl.c.  */
 #if IN_FINDPROG_LGPL || ! GNULIB_FINDPROG_LGPL
@@ -105,22 +108,29 @@ find_in_path (const char *progname)
          design flaw.  */
       if (eaccess (progpathname, X_OK) == 0)
         {
-          /* Found!  */
-          if (strcmp (progpathname, progname) == 0)
+          /* Check that the progpathname does not point to a directory.  */
+          struct stat statbuf;
+
+          if (stat (progpathname, &statbuf) >= 0
+              && ! S_ISDIR (statbuf.st_mode))
             {
-              free (progpathname);
-
-              /* Add the "./" prefix for real, that xconcatenated_filename()
-                 optimized away.  This avoids a second PATH search when the
-                 caller uses execlp/execvp.  */
-              progpathname = XNMALLOC (2 + strlen (progname) + 1, char);
-              progpathname[0] = '.';
-              progpathname[1] = '/';
-              memcpy (progpathname + 2, progname, strlen (progname) + 1);
+              /* Found!  */
+              if (strcmp (progpathname, progname) == 0)
+                {
+                  free (progpathname);
+
+                  /* Add the "./" prefix for real, that xconcatenated_filename()
+                     optimized away.  This avoids a second PATH search when the
+                     caller uses execlp/execvp.  */
+                  progpathname = XNMALLOC (2 + strlen (progname) + 1, char);
+                  progpathname[0] = '.';
+                  progpathname[1] = '/';
+                  memcpy (progpathname + 2, progname, strlen (progname) + 1);
+                }
+
+              free (path);
+              return progpathname;
             }
-
-          free (path);
-          return progpathname;
         }
 
       free (progpathname);