bzero explicit_bzero - escribe bytes cero
Biblioteca Estándar C (
libc,
-lc)
#include <strings.h>
void bzero(void s[.n], size_t n);
#include <string.h>
void explicit_bzero(void s[.n], size_t n);
The
bzero() function erases the data in the
n bytes of the memory
starting at the location pointed to by
s, by writing zeros (bytes
containing '\0') to that area.
The
explicit_bzero() function performs the same task as
bzero().
It differs from
bzero() in that it guarantees that compiler
optimizations will not remove the erase operation if the compiler deduces that
the operation is "unnecessary".
Ninguna.
explicit_bzero() apareció por primera vez en la versión
2.25 de glibc.
Para obtener una explicación de los términos usados en esta
sección, véase
attributes(7).
| Interfaz |
Atributo |
Valor |
|
bzero(), explicit_bzero() |
Seguridad del hilo |
Multi-hilo seguro |
The
bzero() function is deprecated (marked as LEGACY in POSIX.1-2001);
use
memset(3) in new programs. POSIX.1-2008 removes the specification
of
bzero(). The
bzero() function first appeared in 4.3BSD.
La función
explicit_bzero() es una extensión no
estándar presente también algunos BSD. Otras implementaciones
incluyen funciones similares tales como
memset_explicit() o
memset_s().
The
explicit_bzero() function addresses a problem that security-conscious
applications may run into when using
bzero(): if the compiler can
deduce that the location to be zeroed will never again be touched by a
correct program, then it may remove the
bzero() call altogether.
This is a problem if the intent of the
bzero() call was to erase
sensitive data (e.g., passwords) to prevent the possibility that the data was
leaked by an incorrect or compromised program. Calls to
explicit_bzero() are never optimized away by the compiler.
La función
explicit_bzero() no resuelve todos los problemas
relacionados con el borrado de información sensible:
- •
- The explicit_bzero() function does not
guarantee that sensitive data is completely erased from memory. (The same
is true of bzero().) For example, there may be copies of the
sensitive data in a register and in "scratch" stack areas. The
explicit_bzero() function is not aware of these copies, and can't
erase them.
- •
- In some circumstances, explicit_bzero() can
decrease security. If the compiler determined that the variable
containing the sensitive data could be optimized to be stored in a
register (because it is small enough to fit in a register, and no
operation other than the explicit_bzero() call would need to take
the address of the variable), then the explicit_bzero() call will
force the data to be copied from the register to a location in RAM that is
then immediately erased (while the copy in the register remains
unaffected). The problem here is that data in RAM is more likely to be
exposed by a bug than data in a register, and thus the
explicit_bzero() call creates a brief time window where the
sensitive data is more vulnerable than it would otherwise have been if no
attempt had been made to erase the data.
Note that declaring the sensitive variable with the
volatile qualifier
does
not eliminate the above problems. Indeed, it will make them worse,
since, for example, it may force a variable that would otherwise have been
optimized into a register to instead be maintained in (more vulnerable) RAM
for its entire lifetime.
Notwithstanding the above details, for security-conscious applications, using
explicit_bzero() is generally preferable to not using it. The
developers of
explicit_bzero() anticipate that future compilers will
recognize calls to
explicit_bzero() and take steps to ensure that all
copies of the sensitive data are erased, including copies in registers or in
"scratch" stack areas.
bstring(3),
memset(3),
swab(3)
La traducción al español de esta página del manual fue
creada por Sebastian Desimone <
[email protected]>, Cesar D. Lobejon
<
[email protected]>, Miguel Pérez Ibars
<
[email protected]> y Marcos Fouces <
[email protected]>
Esta traducción es documentación libre; lea la
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