[newlib-cygwin/main] Cygwin: fix arc4random after fork(2)

[Corinna Vinschen]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=030a762535c1e18bf5a7ecc73b0f49898a30b157

commit 030a762535c1e18bf5a7ecc73b0f49898a30b157
Author:     Corinna Vinschen <corinna@vinschen.de>
AuthorDate: Mon Jan 29 13:38:14 2024 +0100
Commit:     Corinna Vinschen <corinna@vinschen.de>
CommitDate: Mon Jan 29 13:43:36 2024 +0100

    Cygwin: fix arc4random after fork(2)
    
    After using fork(), arc4random does not reseed itself, which
    causes the results to become predictable.  Activate droppingfork-recognition
    
    Fixes: e0fc33322d50 ("Delete Cygwin's arc4random in favor of new Newlib implementation")
    Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

Diff:
---
 winsup/cygwin/include/machine/_arc4random.h | 11 +++++++++++
 winsup/cygwin/release/3.5.0                 |  6 ++++++
 2 files changed, 17 insertions(+)

diff --git a/winsup/cygwin/include/machine/_arc4random.h b/winsup/cygwin/include/machine/_arc4random.h
index 2078c35972bb..fd3970f64ab2 100644
--- a/winsup/cygwin/include/machine/_arc4random.h
+++ b/winsup/cygwin/include/machine/_arc4random.h
@@ -25,4 +25,15 @@ extern int __isthreaded;
 	    __lock_release (_arc4random_mutex);	\
         } while (0)
 
+static inline void
+_arc4random_forkdetect(void)
+{
+  extern int __in_forkee;
+
+  if (__in_forkee)
+    rs = NULL;
+}
+#define _ARC4RANDOM_FORKDETECT() _arc4random_forkdetect ()
+
+__END_DECLS
 #endif /* _MACHINE_ARC4RANDOM_H */
diff --git a/winsup/cygwin/release/3.5.0 b/winsup/cygwin/release/3.5.0
index 611636b9029d..d756c07853f6 100644
--- a/winsup/cygwin/release/3.5.0
+++ b/winsup/cygwin/release/3.5.0
@@ -67,3 +67,9 @@ What changed:
 
 - The default RLIMIT_CORE is now 0, disabling the generation of core dump or
   stackdump files.
+
+Fixes:
+------
+
+- Fix arc4random reseeding after fork(2).
+  Addresses: https://cygwin.com/pipermail/cygwin/2024-January/255245.html