13586 getcwd() should accept a 0 length argument

Reviewed by: Jason King <jason.king@joyent.com>
Reviewed by: Dan McDonald <danmcd@joyent.com>
Reviewed by: Gordon Ross <gordon.w.ross@gmail.com>
Reviewed by: Robert Mustacchi <rm@fingolfin.org>
Approved by: Rich Lowe <richlowe@richlowe.net>

1 files changed, 48 insertions, 2 deletions

diff --git a/usr/src/lib/libc/port/gen/getcwd.c b/usr/src/lib/libc/port/gen/getcwd.c
index d832d798d7..62f12e027e 100644
--- a/usr/src/lib/libc/port/gen/getcwd.c
+++ b/usr/src/lib/libc/port/gen/getcwd.c
@@ -22,10 +22,9 @@
 /*
  * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
  * Use is subject to license terms.
+ * Copyright 2021 OmniOS Community Edition (OmniOSce) Association.
  */
 
-#pragma ident	"%Z%%M%	%I%	%E% SMI"
-
 /*
  * getcwd() returns the pathname of the current working directory.
  * On error, a NULL pointer is returned and errno is set.
@@ -34,16 +33,63 @@
 #pragma weak _getcwd = getcwd
 
 #include "lint.h"
+#include <sys/param.h>
 #include <sys/syscall.h>
 #include <sys/types.h>
 #include <errno.h>
+#include <limits.h>
 #include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
 
 char *
 getcwd(char *pathname, size_t size)
 {
 	int alloc = 0;
 
+	if (size == 0 && pathname == NULL) {
+		/*
+		 * If no size was provided, start with a buffer that should
+		 * accommodate any normal path and, if it is not big enough,
+		 * keep doubling it to try and make enough space.
+		 *
+		 * Any non-global zone path is longer when observed from the
+		 * global zone, and some filesystems, including ZFS, support
+		 * paths much longer than MAXPATHLEN/_PC_PATH_MAX.
+		 *
+		 * To protect against unbounded memory usage, cap to 128KiB.
+		 * This is an arbitrary limit which is far bigger than the
+		 * length of any practical path on the system.
+		 */
+		if ((size = pathconf(".", _PC_PATH_MAX)) == -1)
+			size = MAXPATHLEN;
+
+		while (size <= 0x20000) {
+			if ((pathname = reallocf(pathname, size)) == NULL) {
+				errno = ENOMEM;
+				return (NULL);
+			}
+			if (syscall(SYS_getcwd, pathname, size) == 0) {
+				char *ret;
+
+				/*
+				 * Shrink the buffer to the length actually
+				 * required to hold the final path.
+				 */
+				ret = realloc(pathname, strlen(pathname) + 1);
+				if (ret == NULL)
+					return (pathname);
+
+				return (ret);
+			}
+			if (errno != ERANGE)
+				break;
+			size <<= 1;
+		}
+		free(pathname);
+		return (NULL);
+	}
+
 	if (size == 0) {
 		errno = EINVAL;
 		return (NULL);