From 758f820bcc0f68aeebac1717e537ca13a320b909 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Sun, 7 Apr 2024 18:11:47 +0200 Subject: Adding upstream version 9.1. Signed-off-by: Daniel Baumann --- lib/freopen-safer.c | 105 ++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 105 insertions(+) create mode 100644 lib/freopen-safer.c (limited to 'lib/freopen-safer.c') diff --git a/lib/freopen-safer.c b/lib/freopen-safer.c new file mode 100644 index 0000000..3bfacee --- /dev/null +++ b/lib/freopen-safer.c @@ -0,0 +1,105 @@ +/* Invoke freopen, but avoid some glitches. + + Copyright (C) 2009-2022 Free Software Foundation, Inc. + + This program is free software: you can redistribute it and/or modify + it under the terms of the GNU General Public License as published by + the Free Software Foundation, either version 3 of the License, or + (at your option) any later version. + + This program is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + GNU General Public License for more details. + + You should have received a copy of the GNU General Public License + along with this program. If not, see . */ + +/* Written by Eric Blake. */ + +#include + +#include "stdio-safer.h" + +#include "attribute.h" + +#include +#include +#include +#include + +/* Guarantee that FD is open; all smaller FDs must already be open. + Return true if successful. */ +static bool +protect_fd (int fd) +{ + int value = open ("/dev/null", O_RDONLY); + if (value != fd) + { + if (0 <= value) + { + close (value); + errno = EBADF; /* Unexpected; this is as good as anything else. */ + } + return false; + } + return true; +} + +/* Like freopen, but guarantee that reopening stdin, stdout, or stderr + preserves the invariant that STDxxx_FILENO==fileno(stdxxx), and + that no other stream will interfere with the standard streams. + This is necessary because most freopen implementations will change + the associated fd of a stream to the lowest available slot. */ + +FILE * +freopen_safer (char const *name, char const *mode, FILE *f) +{ + /* Unfortunately, we cannot use the fopen_safer approach of using + fdopen (dup_safer (fileno (freopen (cmd, mode, f)))), because we + need to return f itself. The implementation of freopen(NULL,m,f) + is system-dependent, so the best we can do is guarantee that all + lower-valued standard fds are open prior to the freopen call, + even though this puts more pressure on open fds. */ + bool protect_in = false; + bool protect_out = false; + bool protect_err = false; + int saved_errno; + + switch (fileno (f)) + { + default: /* -1 or not a standard stream. */ + if (dup2 (STDERR_FILENO, STDERR_FILENO) != STDERR_FILENO) + protect_err = true; + FALLTHROUGH; + case STDERR_FILENO: + if (dup2 (STDOUT_FILENO, STDOUT_FILENO) != STDOUT_FILENO) + protect_out = true; + FALLTHROUGH; + case STDOUT_FILENO: + if (dup2 (STDIN_FILENO, STDIN_FILENO) != STDIN_FILENO) + protect_in = true; + FALLTHROUGH; + case STDIN_FILENO: + /* Nothing left to protect. */ + break; + } + if (protect_in && !protect_fd (STDIN_FILENO)) + f = NULL; + else if (protect_out && !protect_fd (STDOUT_FILENO)) + f = NULL; + else if (protect_err && !protect_fd (STDERR_FILENO)) + f = NULL; + else + f = freopen (name, mode, f); + saved_errno = errno; + if (protect_err) + close (STDERR_FILENO); + if (protect_out) + close (STDOUT_FILENO); + if (protect_in) + close (STDIN_FILENO); + if (!f) + errno = saved_errno; + return f; +} -- cgit v1.2.3