From 9766cc07dcb5964d26fe9e8fd6b1a41b860cea84 Mon Sep 17 00:00:00 2001
From: Simon Ser <contact@emersion.fr>
Date: Wed, 4 Nov 2020 10:28:15 +0100
Subject: [PATCH] Don't rely on PATH_MAX when calling getcwd

References: https://github.com/emersion/mrsh/issues/167
---
 builtin/cd.c         |  9 +++++----
 include/shell/path.h |  2 ++
 shell/entry.c        |  8 +++++---
 shell/path.c         | 19 +++++++++++++++++++
 4 files changed, 31 insertions(+), 7 deletions(-)

diff --git a/builtin/cd.c b/builtin/cd.c
index ca97b93..77a3ebe 100644
--- a/builtin/cd.c
+++ b/builtin/cd.c
@@ -9,6 +9,7 @@
 #include "builtin.h"
 #include "mrsh_getopt.h"
 #include "mrsh_limit.h"
+#include "shell/path.h"
 
 static const char cd_usage[] = "usage: cd [-L|-P] [-|directory]\n";
 
@@ -19,14 +20,14 @@ static int cd(struct mrsh_state *state, const char *path) {
 		fprintf(stderr, "cd: %s\n", strerror(errno));
 		return 1;
 	}
-	char cwd[PATH_MAX];
-	if (getcwd(cwd, PATH_MAX) == NULL) {
-		fprintf(stderr, "cd: Cannot set new PWD as the path "
-			"is too long\n");
+	char *cwd = current_working_dir();
+	if (cwd == NULL) {
+		perror("current_working_dir failed");
 		return 1;
 	}
 	mrsh_env_set(state, "OLDPWD", oldPWD, MRSH_VAR_ATTRIB_NONE);
 	mrsh_env_set(state, "PWD", cwd, MRSH_VAR_ATTRIB_EXPORT);
+	free(cwd);
 	return 0;
 }
 
diff --git a/include/shell/path.h b/include/shell/path.h
index 932563b..14cf490 100644
--- a/include/shell/path.h
+++ b/include/shell/path.h
@@ -12,5 +12,7 @@
  */
 char *expand_path(struct mrsh_state *state, const char *file, bool exec,
 	bool default_path);
+/* Like getcwd, but returns allocated memory */
+char *current_working_dir(void);
 
 #endif
diff --git a/shell/entry.c b/shell/entry.c
index 2ef81a7..75f19e8 100644
--- a/shell/entry.c
+++ b/shell/entry.c
@@ -9,6 +9,7 @@
 #include <unistd.h>
 #include "builtin.h"
 #include "parser.h"
+#include "shell/path.h"
 #include "shell/trap.h"
 #include "mrsh_limit.h"
 
@@ -98,13 +99,14 @@ bool mrsh_populate_env(struct mrsh_state *state, char **environ) {
 	// TODO check if path is well-formed, has . or .., and handle symbolic links
 	const char *pwd = mrsh_env_get(state, "PWD", NULL);
 	if (pwd == NULL || strlen(pwd) >= PATH_MAX) {
-		char cwd[PATH_MAX];
-		if (getcwd(cwd, PATH_MAX) == NULL) {
-			perror("getcwd");
+		char *cwd = current_working_dir();
+		if (cwd == NULL) {
+			perror("current_working_dir failed");
 			return false;
 		}
 		mrsh_env_set(state, "PWD", cwd,
 				MRSH_VAR_ATTRIB_EXPORT | MRSH_VAR_ATTRIB_READONLY);
+		free(cwd);
 	} else {
 		mrsh_env_set(state, "PWD", pwd,
 				MRSH_VAR_ATTRIB_EXPORT | MRSH_VAR_ATTRIB_READONLY);
diff --git a/shell/path.c b/shell/path.c
index f361211..2d6ad72 100644
--- a/shell/path.c
+++ b/shell/path.c
@@ -1,4 +1,6 @@
 #define _POSIX_C_SOURCE 200809L
+#include <errno.h>
+#include <mrsh/buffer.h>
 #include <mrsh/shell.h>
 #include <string.h>
 #include <stdbool.h>
@@ -64,3 +66,20 @@ next:
 	free(pathe);
 	return NULL;
 }
+
+char *current_working_dir(void) {
+	// POSIX doesn't provide a way to query the CWD size
+	struct mrsh_buffer buf = {0};
+	if (mrsh_buffer_reserve(&buf, 256) == NULL) {
+		return NULL;
+	}
+	while (getcwd(buf.data, buf.cap) == NULL) {
+		if (errno != ERANGE) {
+			return NULL;
+		}
+		if (mrsh_buffer_reserve(&buf, buf.cap * 2) == NULL) {
+			return NULL;
+		}
+	}
+	return mrsh_buffer_steal(&buf);
+}
-- 
2.45.2