[PATCH] cygwin: pread/pwrite: prevent EBADF error after fork()

[Christian Franke]

This addresses: 
https://sourceware.org/pipermail/cygwin/2024-September/256468.html

-- 
Regards,
Christian

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From a688e962eb493140010a75dc24b6b49b34b7d558 Mon Sep 17 00:00:00 2001
From: Christian Franke <christian.franke@t-online.de>
Date: Tue, 24 Sep 2024 11:56:43 +0200
Subject: [PATCH] cygwin: pread/pwrite: prevent EBADF error after fork()

If the parent process has already used pread() or pwrite(), these
functions fail with EBADF if used on the inherited fd.  Ensure that
fix_after_fork() is called to invalidate the prw_handle. This issue
has been detected by 'stress-ng --pseek 1'.

Signed-off-by: Christian Franke <christian.franke@t-online.de>
---
 winsup/cygwin/fhandler/disk_file.cc | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/winsup/cygwin/fhandler/disk_file.cc b/winsup/cygwin/fhandler/disk_file.cc
index f4c21d3b7..2008fb61b 100644
--- a/winsup/cygwin/fhandler/disk_file.cc
+++ b/winsup/cygwin/fhandler/disk_file.cc
@@ -1803,6 +1803,9 @@ fhandler_disk_file::prw_open (bool write, void *aio)
       return -1;
     }
 
+  /* prw_handle is invalid after fork. */
+  need_fork_fixup (true);
+
   /* record prw_handle's asyncness for subsequent pread/pwrite operations */
   prw_handle_isasync = !!aio;
   return 0;
-- 
2.45.1