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d40ac01cbb
The recursive lock used on abort does not synchronize with a new process
creation (either by fork-like interfaces or posix_spawn ones), nor it
is reinitialized after fork().
Also, the SIGABRT unblock before raise() shows another race condition,
where a fork or posix_spawn() call by another thread, just after the
recursive lock release and before the SIGABRT signal, might create
programs with a non-expected signal mask. With the default option
(without POSIX_SPAWN_SETSIGDEF), the process can see SIG_DFL for
SIGABRT, where it should be SIG_IGN.
To fix the AS-safe, raise() does not change the process signal mask,
and an AS-safe lock is used if a SIGABRT is installed or the process
is blocked or ignored. With the signal mask change removal,
there is no need to use a recursive loc. The lock is also taken on
both _Fork() and posix_spawn(), to avoid the spawn process to see the
abort handler as SIG_DFL.
A read-write lock is used to avoid serialize _Fork and posix_spawn
execution. Both sigaction (SIGABRT) and abort() requires to lock
as writer (since both change the disposition).
The fallback is also simplified: there is no need to use a loop of
ABORT_INSTRUCTION after _exit() (if the syscall does not terminate the
process, the system is broken).
The proposed fix changes how setjmp works on a SIGABRT handler, where
glibc does not save the signal mask. So usage like the below will now
always abort.
static volatile int chk_fail_ok;
static jmp_buf chk_fail_buf;
static void
handler (int sig)
{
if (chk_fail_ok)
{
chk_fail_ok = 0;
longjmp (chk_fail_buf, 1);
}
else
_exit (127);
}
[...]
signal (SIGABRT, handler);
[....]
chk_fail_ok = 1;
if (! setjmp (chk_fail_buf))
{
// Something that can calls abort, like a failed fortify function.
chk_fail_ok = 0;
printf ("FAIL\n");
}
Such cases will need to use sigsetjmp instead.
The _dl_start_profile calls sigaction through _profil, and to avoid
pulling abort() on loader the call is replaced with __libc_sigaction.
Checked on x86_64-linux-gnu and aarch64-linux-gnu.
Reviewed-by: DJ Delorie <dj@redhat.com>
105 lines
2.7 KiB
C
105 lines
2.7 KiB
C
/* Fortify check for wprintf.
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Copyright (C) 2023-2024 Free Software Foundation, Inc.
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Copyright The GNU Toolchain Authors.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <setjmp.h>
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#include <stdio.h>
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#include <wchar.h>
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#include <unistd.h>
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#include <support/support.h>
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static volatile int chk_fail_ok;
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static volatile int ret;
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static sigjmp_buf chk_fail_buf;
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static void
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handler (int sig)
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{
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if (chk_fail_ok)
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{
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chk_fail_ok = 0;
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longjmp (chk_fail_buf, 1);
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}
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else
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_exit (127);
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}
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static const wchar_t *wstr3 = L"%ls%n%ls%n";
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static const wchar_t *wstr4 = L"Hello, ";
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static const wchar_t *wstr5 = L"World!\n";
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static wchar_t wbuf2[20] = L"%ls";
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#define WFAIL \
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do { wprintf (L"Failure on line %d\n", __LINE__); ret = 1; } while (0)
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#define CHK_FAIL_START \
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chk_fail_ok = 1; \
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if (! sigsetjmp (chk_fail_buf, 1)) \
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{
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#define CHK_FAIL_END \
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chk_fail_ok = 0; \
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WFAIL; \
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}
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static int
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do_test (void)
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{
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set_fortify_handler (handler);
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int n1, n2;
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int orientation = fwide (stdout, 1);
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if (orientation <= 0)
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WFAIL;
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/* Constant literals passed directly are always ok
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(even with warnings about possible bugs from GCC). */
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if (wprintf (L"%ls%n%ls%n", wstr4, &n1, wstr5, &n2) != 14
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|| n1 != 7 || n2 != 14)
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WFAIL;
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/* In this case the format string is not known at compile time,
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but resides in read-only memory, so is ok. */
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if (wprintf (wstr3, wstr4, &n1, wstr5, &n2) != 14
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|| n1 != 7 || n2 != 14)
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WFAIL;
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wcpcpy (&wbuf2[3], L"%n%ls%n");
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/* When the format string is writable and contains %n,
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with -D_FORTIFY_SOURCE=2 it causes __chk_fail. */
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CHK_FAIL_START
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if (wprintf (wbuf2, wstr4, &n1, wstr5, &n1) != 14)
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WFAIL;
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CHK_FAIL_END
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/* But if there is no %n, even writable format string
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should work. */
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wbuf2[8] = L'\0';
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if (wprintf (&wbuf2[5], wstr5) != 7)
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WFAIL;
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/* Check whether missing N$ formats are detected. */
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CHK_FAIL_START
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wprintf (L"%3$d\n", 1, 2, 3, 4);
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CHK_FAIL_END
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return ret;
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}
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#include <support/test-driver.c>
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