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core: randomize hash seed with a global seed

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This makes hashing non-deterministic with the aim to
make it harder to exploit hash collisions.

Non-deterministic also means that for unit testing
we will get different values on each run. But since we
shall never assign any meaning to these hash values
nor rely on them being stable between restarts (or
upgrades), that doesn't hurt.
This commit is contained in:
Thomas Haller 2017-10-13 11:56:06 +02:00
parent 4a2798434e
commit c978b9dfe5
2 changed files with 24 additions and 5 deletions
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23
shared/nm-utils/nm-shared-utils.c
View file

@ -863,6 +863,29 @@ nm_g_object_class_find_property_from_gtype (GType gtype,
/*****************************************************************************/
guint
NM_HASH_INIT (guint seed)
{
static volatile guint global_seed = 0;
guint g, s;
/* we xor @seed with a random @global_seed. This is to make the hashing behavior
* less predictable and harder to exploit collisions. */
g = global_seed;
if (G_UNLIKELY (g == 0)) {
nm_utils_random_bytes (&s, sizeof (s));
if (s == 0)
s = 42;
g_atomic_int_compare_and_exchange ((int *) &global_seed, 0, s);
g = global_seed;
nm_assert (g);
}
return g ^ seed;
}
/*****************************************************************************/
static void
_str_append_escape (GString *s, char ch)
{

6
shared/nm-utils/nm-shared-utils.h
View file

@ -378,11 +378,7 @@ GParamSpec *nm_g_object_class_find_property_from_gtype (GType gtype,
/*****************************************************************************/
static inline guint
NM_HASH_INIT (guint seed)
{
return seed;
}
guint NM_HASH_INIT (guint seed);
static inline guint
NM_HASH_COMBINE (guint h, guint val)