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Implement _dl_catch_error, _dl_signal_error in libc.so [BZ #16628]

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This change moves the main implementation of _dl_catch_error,
_dl_signal_error to libc.so, where TLS variables can be used
directly.  This removes a writable function pointer from the
rtld_global variable.

For use during initial relocation, minimal implementations of these
functions are provided in ld.so.  These are eventually interposed
by the libc.so implementations.  This is implemented by compiling
elf/dl-error-skeleton.c twice, via elf/dl-error.c and
elf/dl-error-minimal.c.

As a side effect of this change, the static version of dl-error.c
no longer includes support for the
_dl_signal_cerror/_dl_receive_error mechanism because it is only
used in ld.so.
This commit is contained in:
Florian Weimer
2016-11-30 15:59:57 +01:00
parent 705a79f825
commit 9e78f6f6e7
37 changed files with 595 additions and 315 deletions
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210
elf/dl-error.c
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@@ -1,4 +1,4 @@
/* Error handling for runtime dynamic linker.
/* Error handling for runtime dynamic linker, full version.
Copyright (C) 1995-2016 Free Software Foundation, Inc.
This file is part of the GNU C Library.
@@ -16,206 +16,12 @@
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
#include <libintl.h>
#include <setjmp.h>
#include <stdbool.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <ldsodefs.h>
/* This implementation lives in libc.so because it uses thread-local
data, which is not available in ld.so. It interposes the version
in dl-error-minimal.c after ld.so bootstrap.
/* This structure communicates state between _dl_catch_error and
_dl_signal_error. */
struct catch
{
const char **objname; /* Object/File name. */
const char **errstring; /* Error detail filled in here. */
bool *malloced; /* Nonzero if the string is malloced
by the libc malloc. */
volatile int *errcode; /* Return value of _dl_signal_error. */
jmp_buf env; /* longjmp here on error. */
};
The signal/catch mechanism is used by the audit framework, which
means that even in ld.so, not all errors are fatal. */
/* Multiple threads at once can use the `_dl_catch_error' function. The
calls can come from `_dl_map_object_deps', `_dlerror_run', or from
any of the libc functionality which loads dynamic objects (NSS, iconv).
Therefore we have to be prepared to save the state in thread-local
memory. The _dl_error_catch_tsd function pointer is reset by the thread
library so that it returns the address of a thread-local variable. */
/* This message we return as a last resort. We define the string in a
variable since we have to avoid freeing it and so have to enable
a pointer comparison. See below and in dlfcn/dlerror.c. */
static const char _dl_out_of_memory[] = "out of memory";
/* This points to a function which is called when an continuable error is
received. Unlike the handling of `catch' this function may return.
The arguments will be the `errstring' and `objname'.
Since this functionality is not used in normal programs (only in ld.so)
we do not care about multi-threaded programs here. We keep this as a
global variable. */
static receiver_fct receiver;
#ifdef _LIBC_REENTRANT
# define CATCH_HOOK (*(struct catch **) (*GL(dl_error_catch_tsd)) ())
#else
static struct catch *catch_hook;
# define CATCH_HOOK catch_hook
#endif
void
internal_function
_dl_signal_error (int errcode, const char *objname, const char *occation,
const char *errstring)
{
struct catch *lcatch;
if (! errstring)
errstring = N_("DYNAMIC LINKER BUG!!!");
lcatch = CATCH_HOOK;
if (objname == NULL)
objname = "";
if (lcatch != NULL)
{
/* We are inside _dl_catch_error. Return to it. We have to
duplicate the error string since it might be allocated on the
stack. The object name is always a string constant. */
size_t len_objname = strlen (objname) + 1;
size_t len_errstring = strlen (errstring) + 1;
char *errstring_copy = malloc (len_objname + len_errstring);
if (errstring_copy != NULL)
{
/* Make a copy of the object file name and the error string. */
*lcatch->objname = memcpy (__mempcpy (errstring_copy,
errstring, len_errstring),
objname, len_objname);
*lcatch->errstring = errstring_copy;
/* If the main executable is relocated it means the libc's malloc
is used. */
bool malloced = true;
#ifdef SHARED
malloced = (GL(dl_ns)[LM_ID_BASE]._ns_loaded != NULL
&& (GL(dl_ns)[LM_ID_BASE]._ns_loaded->l_relocated != 0));
#endif
*lcatch->malloced = malloced;
}
else
{
/* This is better than nothing. */
*lcatch->objname = "";
*lcatch->errstring = _dl_out_of_memory;
*lcatch->malloced = false;
}
*lcatch->errcode = errcode;
/* We do not restore the signal mask because none was saved. */
__longjmp (lcatch->env[0].__jmpbuf, 1);
}
else
{
/* Lossage while resolving the program's own symbols is always fatal. */
char buffer[1024];
_dl_fatal_printf ("%s: %s: %s%s%s%s%s\n",
RTLD_PROGNAME,
occation ?: N_("error while loading shared libraries"),
objname, *objname ? ": " : "",
errstring, errcode ? ": " : "",
(errcode
? __strerror_r (errcode, buffer, sizeof buffer)
: ""));
}
}
void
internal_function
_dl_signal_cerror (int errcode, const char *objname, const char *occation,
const char *errstring)
{
if (__builtin_expect (GLRO(dl_debug_mask)
& ~(DL_DEBUG_STATISTICS|DL_DEBUG_PRELINK), 0))
_dl_debug_printf ("%s: error: %s: %s (%s)\n", objname, occation,
errstring, receiver ? "continued" : "fatal");
if (receiver)
{
/* We are inside _dl_receive_error. Call the user supplied
handler and resume the work. The receiver will still be
installed. */
(*receiver) (errcode, objname, errstring);
}
else
_dl_signal_error (errcode, objname, occation, errstring);
}
int
internal_function
_dl_catch_error (const char **objname, const char **errstring,
bool *mallocedp, void (*operate) (void *), void *args)
{
/* We need not handle `receiver' since setting a `catch' is handled
before it. */
/* Only this needs to be marked volatile, because it is the only local
variable that gets changed between the setjmp invocation and the
longjmp call. All others are just set here (before setjmp) and read
in _dl_signal_error (before longjmp). */
volatile int errcode;
struct catch c;
/* Don't use an initializer since we don't need to clear C.env. */
c.objname = objname;
c.errstring = errstring;
c.malloced = mallocedp;
c.errcode = &errcode;
struct catch **const catchp = &CATCH_HOOK;
struct catch *const old = *catchp;
*catchp = &c;
/* Do not save the signal mask. */
if (__builtin_expect (__sigsetjmp (c.env, 0), 0) == 0)
{
(*operate) (args);
*catchp = old;
*objname = NULL;
*errstring = NULL;
*mallocedp = false;
return 0;
}
/* We get here only if we longjmp'd out of OPERATE. _dl_signal_error has
already stored values into *OBJNAME, *ERRSTRING, and *MALLOCEDP. */
*catchp = old;
return errcode;
}
void
internal_function
_dl_receive_error (receiver_fct fct, void (*operate) (void *), void *args)
{
struct catch **const catchp = &CATCH_HOOK;
struct catch *old_catch;
receiver_fct old_receiver;
old_catch = *catchp;
old_receiver = receiver;
/* Set the new values. */
*catchp = NULL;
receiver = fct;
(*operate) (args);
*catchp = old_catch;
receiver = old_receiver;
}
#define DL_ERROR_BOOTSTRAP 0
#include "dl-error-skeleton.c"