[PATCH][API-CONFORMAANCE] Increase SYMLOOP_MAX to 63

[Sebastian Feld]

On Tue, Jun 17, 2025 at 1:16 PM Corinna Vinschen
<corinna-cygwin@cygwin.com> wrote:
>
> Hi Sebastian,
>
> On Jun 17 09:48, Sebastian Feld wrote:
> > The following patch increases from 10 to 63, per Windows spec
> > https://learn.microsoft.com/en-us/windows/win32/fileio/reparse-points
> >
> > Security impact is minor, SYMLOOP_MAX is just an artificial limiter to
> > prevent endless loops.
>
> In case of Cygwin (Cygwin is slow, we all know that), the rather low
> SYMLOOP_MAX was chosen so the path handling didn't get even slower in
> some circumstances I don't remember anymore.  Maybe the times when this
> was relevant are over, so we can try this.

1. Cygwin is NOT slow. Who says that?
2. If there is a performance impact, then this should be documented in
the source code.

> However, please send a real git patch created with `git format-patch'
> and don't forget your Signed-off-by:".

Patch attached.

Are there CI or regression test scripts where I could add a test module?

Sebi
-- 
Sebastian Feld - IT security consultant
-------------- next part --------------
From f7fcee85a6001a42569954a5cc0faf9cbed7ee04 Mon Sep 17 00:00:00 2001
From: Sebastian Feld <sebastian.n.feld@gmail.com>
Date: Fri, 20 Jun 2025 13:19:23 +0200
Subject: [PATCH] Increase SYMLOOP_MAX limit to 63 per Win32 spec

Increase SYMLOOP_MAX limit to 63 per Win32 spec.

The spec at https://learn.microsoft.com/en-us/windows/win32/fileio/reparse-points
says:
... There is a limit of 63 reparse points on any given path.
NOTE: The limit can be reduced depending on the length of the
reparse point. For example, if your reparse point targets a fully
qualified path, the limit becomes 31. */

Signed-off-by: Sebastian Feld <sebastian.n.feld@gmail.com>
---
 winsup/cygwin/include/cygwin/limits.h | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/winsup/cygwin/include/cygwin/limits.h b/winsup/cygwin/include/cygwin/limits.h
index 204154da9..728dfd47b 100644
--- a/winsup/cygwin/include/cygwin/limits.h
+++ b/winsup/cygwin/include/cygwin/limits.h
@@ -43,7 +43,13 @@ details. */
 #define __SEM_VALUE_MAX 1147483648
 #define __SIGQUEUE_MAX 1024
 #define __STREAM_MAX 20
-#define __SYMLOOP_MAX 10
+/* __SYMLOOP_MAX
+   https://learn.microsoft.com/en-us/windows/win32/fileio/reparse-points
+   ... There is a limit of 63 reparse points on any given path.
+   NOTE: The limit can be reduced depending on the length of the
+   reparse point. For example, if your reparse point targets a fully
+   qualified path, the limit becomes 31. */
+#define __SYMLOOP_MAX 63
 #define __TIMER_MAX 32
 #define __TTY_NAME_MAX 32
 #define __FILESIZEBITS 64
-- 
2.30.2