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Ensure memory cleaning

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Compilers are allowed to and do optimize memset(3) calls away for
pointers not accessed in the future. Since the memzero wrappers purpose
is exactly to unconditionally override memory (e.g. for stored
passwords) do not implement via regular memset(3), but via either
memset_s(3), explicit_bzero(3) or a hand written implementation using
volatile pointers.

See https://wiki.sei.cmu.edu/confluence/display/c/MSC06-C.+Beware+of+compiler+optimizations
This commit is contained in:
Christian Göttsche
2022-01-03 15:03:34 +01:00
parent eccf1c569c
commit 7a799ebb2c
2 changed files with 15 additions and 2 deletions
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15
lib/defines.h
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@@ -111,7 +111,20 @@ char *strchr (), *strrchr (), *strtok ();
# endif
#endif /* not TIME_WITH_SYS_TIME */
#define memzero(ptr, size) memset((void *)(ptr), 0, (size))
#ifdef HAVE_MEMSET_S
# define memzero(ptr, size) memset_s((ptr), 0, (size))
#elif defined HAVE_EXPLICIT_BZERO /* !HAVE_MEMSET_S */
# define memzero(ptr, size) explicit_bzero((ptr), (size))
#else /* !HAVE_MEMSET_S && HAVE_EXPLICIT_BZERO */
static inline void memzero(void *ptr, size_t size)
{
volatile unsigned char * volatile p = ptr;
while (size--) {
*p++ = '\0';
}
}
#endif /* !HAVE_MEMSET_S && !HAVE_EXPLICIT_BZERO */
#define strzero(s) memzero(s, strlen(s)) /* warning: evaluates twice */
#ifdef HAVE_DIRENT_H /* DIR_SYSV */