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NOMBRE
bzero explicit_bzero - escribe bytes cero
BIBLIOTECA
Biblioteca Estándar C (libc, -lc)
SINOPSIS
#include <strings.h> void bzero(void s[.n], size_t n); #include <string.h> void explicit_bzero(void s[.n], size_t n);
DESCRIPCIÓN
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".
VALOR DEVUELTO
Ninguna.
VERSIONES
explicit_bzero() apareció por primera vez en la versión 2.25 de glibc.
ATRIBUTOS
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 │ └───────────────────────────────────────────────────────────────┴────────────────────┴───────────────────┘
ESTÁNDARES
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().
NOTAS
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.
VÉASE TAMBIÉN
bstring(3), memset(3), swab(3)
TRADUCCIÓN
La traducción al español de esta página del manual fue creada por Sebastian Desimone
<chipy@argenet.com.ar>, Cesar D. Lobejon <cesar@alien.mec.es>, Miguel Pérez Ibars <mpi79470@alu.um.es> y
Marcos Fouces <marcos@debian.org>
Esta traducción es documentación libre; lea la GNU General Public License Version 3
⟨https://www.gnu.org/licenses/gpl-3.0.html⟩ o posterior con respecto a las condiciones de copyright. No
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