[PATCH 2/2] run-command: Add interpreter permissions check

@@ -194,6 +194,63 @@ static int have_read_execute_permissions(const char *path)
 	return 0;
 }
 
+static void check_interpreter(const char *cmd)
+{
+	FILE *f;
+	struct strbuf sb = STRBUF_INIT;
+	/* bash reads an 80 character line when determining the interpreter.
+	 * BSD apparently only allows 32 characters, as it is the size of
+	 * your average binary executable header.
+	 */
+	char firstline[80];
+	char *interpreter = NULL;
+	size_t s, i;
+
+	f = fopen(cmd, "r");
+	if (!f) {
+		error("cannot open file '%s': %s\n", cmd, strerror(errno));
+		return;
+	}
+
+	s = fread(firstline, 1, sizeof(firstline), f);
+	if (s < 2) {
+		trace_printf("cannot determine file type");
+		fclose(f);
+		return;
+	}
+
+	if (firstline[0] != '#' || firstline[1] != '!') {
+		trace_printf("file '%s' is not a script or"
+				" is a script without '#!'", cmd);
+		fclose(f);
+		return;
+	}
+
+	/* see if the given path has the executable bit set */
+	for (i = 2; i < s; i++) {
+		if (!interpreter && firstline[i] != ' ' && firstline[i] != '\t')
+			interpreter = firstline + i;
+
+		if (interpreter && (firstline[i] == ' ' ||
+				firstline[i] == '\n')) {
+			strbuf_add(&sb, interpreter,
+					(firstline + i) - interpreter);
+			break;
+		}
+	}
+	if (!sb.len) {
+		error("could not determine interpreter");
+		strbuf_release(&sb);
+		return;
+	}
+
+	if (!have_read_execute_permissions(sb.buf))
+		error("bad interpreter: no read/execute permissions on '%s'\n",
+				sb.buf);
+
+	strbuf_release(&sb);
+}
+
 static void diagnose_execvp_eacces(const char *cmd, const char **argv)
 {
 	/* man 2 execve states that EACCES is returned for:

@@ -209,8 +266,8 @@ static void diagnose_execvp_eacces(const char *cmd, const char **argv)
 	char *next;
 
 	if (strchr(cmd, '/')) {
-		if (!have_read_execute_permissions(cmd))
-			error("no read/execute permissions on '%s'\n", cmd);
+		if (have_read_execute_permissions(cmd))
+			check_interpreter(cmd);
 		return;
 	}
 

@@ -233,10 +290,7 @@ static void diagnose_execvp_eacces(const char *cmd, const char **argv)
 				error("no read/execute permissions on '%s'\n",
 						sb.buf);
 			else
-				warn("file '%s' exists and permissions "
-				"seem OK.\nIf this is a script, see if you "
-				"have sufficient privileges to run the "
-				"interpreter", sb.buf);
+				check_interpreter(sb.buf);
 		}
 
 		strbuf_release(&sb);

@@ -13,6 +13,18 @@ cat >hello-script <<-EOF
 EOF
 >empty
 
+cat >someinterpreter <<-EOF
+	#!$SHELL_PATH
+	cat hello-script
+EOF
+>empty
+
+cat >incorrect-interpreter-script <<-EOF
+	#!someinterpreter
+	cat hello-script
+EOF
+>empty
+
 test_expect_success 'start_command reports ENOENT' '
 	test-run-command start-command-ENOENT ./does-not-exist
 '

@@ -48,4 +60,14 @@ test_expect_success POSIXPERM 'run_command reports EACCES, search path permision
 	grep "no read/execute permissions on" err
 '
 
+test_expect_success POSIXPERM 'run_command reports EACCES, interpreter fails' '
+	cat incorrect-interpreter-script >hello.sh &&
+	chmod +x hello.sh &&
+	chmod -x someinterpreter &&
+	test_must_fail test-run-command run-command ./hello.sh 2>err &&
+
+	grep "fatal: cannot exec.*hello.sh" err &&
+	grep "bad interpreter" err
+'
+
 test_done