00457: ssl: Raise OSError for ERR_LIB_SYS

The patch resolves the flakiness of test_ftplib

Backported from upstream 3.10+:
python#127361

Co-authored-by: Petr Viktorin <[email protected]>

Author: 2 people

Modules/_ssl.c

@@ -638,6 +638,11 @@ PySSL_SetError(PySSLSocket *obj, int ret, const char *filename, int lineno)
                     errstr = "Some I/O error occurred";
                 }
             } else {
+                if (ERR_GET_LIB(e) == ERR_LIB_SYS) {
+                    // A system error is being reported; reason is set to errno
+                    errno = ERR_GET_REASON(e);
+                    return PyErr_SetFromErrno(PyExc_OSError);
+                }
                 p = PY_SSL_ERROR_SYSCALL;
             }
             break;
@@ -648,6 +653,11 @@ PySSL_SetError(PySSLSocket *obj, int ret, const char *filename, int lineno)
             if (e == 0)
                 /* possible? */
                 errstr = "A failure in the SSL library occurred";
+            if (ERR_GET_LIB(e) == ERR_LIB_SYS) {
+                // A system error is being reported; reason is set to errno
+                errno = ERR_GET_REASON(e);
+                return PyErr_SetFromErrno(PyExc_OSError);
+            }
             break;
         }
         default: