Avoid integer overflow in posix_open on Windows

If open() fails, return the error value immediately. Adding the high bit
to -1 results in a large positive integer, which causes callers like
tls_config_load_file() to bypass their error checks.

Fix https://github.com/libressl/portable/issues/1239

1 files changed, 3 insertions, 0 deletions

diff --git a/crypto/compat/posix_win.c b/crypto/compat/posix_win.c
index 572e527..00d3d82 100644
--- a/crypto/compat/posix_win.c
+++ b/crypto/compat/posix_win.c
@@ -89,6 +89,9 @@ posix_open(const char *path, ...)
         flags &= ~O_NONBLOCK;
 
         const int fh = open(path, flags, mode);
+        if (fh < 0) {
+                return fh;
+        }
 
         // Set high bit to mark file descriptor as a file handle
         return fh + 0x80000000;