libbb: fix empty PATH components handling

function                                             old     new   delta
find_execable                                         81      86      +5
exists_execable                                       71      66      -5

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 18 insertions, 12 deletions

diff --git a/libbb/execable.c b/libbb/execable.c
index 178a00a5f..a3caea6f9 100644
--- a/libbb/execable.c
+++ b/libbb/execable.c
@@ -30,6 +30,14 @@ int FAST_FUNC execable_file(const char *name)
  */
 char* FAST_FUNC find_execable(const char *filename, char **PATHp)
 {
+        /* About empty components in $PATH:
+         * http://pubs.opengroup.org/onlinepubs/009695399/basedefs/xbd_chap08.html
+         * 8.3 Other Environment Variables - PATH
+         * A zero-length prefix is a legacy feature that indicates the current
+         * working directory. It appears as two adjacent colons ( "::" ), as an
+         * initial colon preceding the rest of the list, or as a trailing colon
+         * following the rest of the list.
+         */
         char *p, *n;
 
         p = *PATHp;
@@ -37,14 +45,15 @@ char* FAST_FUNC find_execable(const char *filename, char **PATHp)
                 n = strchr(p, ':');
                 if (n)
                         *n++ = '\0';
-                if (*p != '\0') { /* it's not a PATH="foo::bar" situation */
-                        p = concat_path_file(p, filename);
-                        if (execable_file(p)) {
-                                *PATHp = n;
-                                return p;
-                        }
-                        free(p);
+                p = concat_path_file(
+                        p[0] ? p : ".", /* handle "::" case */
+                        filename
+                );
+                if (execable_file(p)) {
+                        *PATHp = n;
+                        return p;
                 }
+                free(p);
                 p = n;
         } /* on loop exit p == NULL */
         return p;
@@ -60,11 +69,8 @@ int FAST_FUNC exists_execable(const char *filename)
         char *tmp = path;
         char *ret = find_execable(filename, &tmp);
         free(path);
-        if (ret) {
-                free(ret);
-                return 1;
-        }
-        return 0;
+        free(ret);
+        return ret != NULL;
 }
 
 #if ENABLE_FEATURE_PREFER_APPLETS