[PATCH] Cygwin: rmdir: fail if last component is a symlink, as on Linux

[Ken Brown]

If the last component of the directory name is a symlink followed by a
slash, rmdir should fail, even if the symlink resolves to an existing
empty directory.

mkdir was similarly fixed in 2009 in commit
52dba6a5c45e8d8ba1e237a15213311dc11d91fb.  Modify a comment to clarify
the purpose of that commit.

Addresses https://cygwin.com/ml/cygwin/2019-09/msg00221.html.
---
 winsup/cygwin/dir.cc | 26 ++++++++++++++++++++++----
 1 file changed, 22 insertions(+), 4 deletions(-)

diff --git a/winsup/cygwin/dir.cc b/winsup/cygwin/dir.cc
index b757851d5..f65c9bdad 100644
--- a/winsup/cygwin/dir.cc
+++ b/winsup/cygwin/dir.cc
@@ -305,15 +305,14 @@ mkdir (const char *dir, mode_t mode)
 
   __try
     {
-      /* POSIX says mkdir("symlink-to-missing/") should create the
-	 directory "missing", but Linux rejects it with EEXIST.  Copy
-	 Linux behavior for now.  */
-
       if (!*dir)
 	{
 	  set_errno (ENOENT);
 	  __leave;
 	}
+      /* Following Linux, do not resolve the last component of DIR if
+	 it is a symlink, even if DIR has a trailing slash.  Achieve
+	 this by stripping trailing slashes or backslashes.  */
       if (isdirsep (dir[strlen (dir) - 1]))
 	{
 	  /* This converts // to /, but since both give EEXIST, we're okay.  */
@@ -354,6 +353,25 @@ rmdir (const char *dir)
 
   __try
     {
+      if (!*dir)
+	{
+	  set_errno (ENOENT);
+	  __leave;
+	}
+
+      /* Following Linux, do not resolve the last component of DIR if
+	 it is a symlink, even if DIR has a trailing slash.  Achieve
+	 this by stripping trailing slashes or backslashes.  */
+      if (isdirsep (dir[strlen (dir) - 1]))
+	{
+	  /* This converts // to /, but since both give ENOTEMPTY,
+	     we're okay.  */
+	  char *buf;
+	  char *p = stpcpy (buf = tp.c_get (), dir) - 1;
+	  dir = buf;
+	  while (p > dir && isdirsep (*p))
+	    *p-- = '\0';
+	}
       if (!(fh = build_fh_name (dir, PC_SYM_NOFOLLOW)))
 	__leave;   /* errno already set */;
 
-- 
2.21.0