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random: add backtracking protection to the CRNG

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Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Theodore Ts'o 2016-05-04 13:29:18 -04:00
parent 1e7f583af6
commit c92e040d57
1 changed files with 49 additions and 5 deletions
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54
drivers/char/random.c
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@ -438,7 +438,8 @@ static int crng_init_cnt = 0;
#define CRNG_INIT_CNT_THRESH (2*CHACHA20_KEY_SIZE) #define CRNG_INIT_CNT_THRESH (2*CHACHA20_KEY_SIZE)
static void _extract_crng(struct crng_state *crng, static void _extract_crng(struct crng_state *crng,
__u8 out[CHACHA20_BLOCK_SIZE]); __u8 out[CHACHA20_BLOCK_SIZE]);
static void extract_crng(__u8 out[CHACHA20_BLOCK_SIZE]); static void _crng_backtrack_protect(struct crng_state *crng,
__u8 tmp[CHACHA20_BLOCK_SIZE], int used);
static void process_random_ready_list(void); static void process_random_ready_list(void);
/********************************************************************** /**********************************************************************
@ -826,8 +827,11 @@ static void crng_reseed(struct crng_state *crng, struct entropy_store *r)
num = extract_entropy(r, &buf, 32, 16, 0); num = extract_entropy(r, &buf, 32, 16, 0);
if (num == 0) if (num == 0)
return; return;
} else } else {
_extract_crng(&primary_crng, buf.block); _extract_crng(&primary_crng, buf.block);
_crng_backtrack_protect(&primary_crng, buf.block,
CHACHA20_KEY_SIZE);
}
spin_lock_irqsave(&primary_crng.lock, flags); spin_lock_irqsave(&primary_crng.lock, flags);
for (i = 0; i < 8; i++) { for (i = 0; i < 8; i++) {
unsigned long rv; unsigned long rv;
@ -889,9 +893,46 @@ static void extract_crng(__u8 out[CHACHA20_BLOCK_SIZE])
_extract_crng(crng, out); _extract_crng(crng, out);
} }
/*
* Use the leftover bytes from the CRNG block output (if there is
* enough) to mutate the CRNG key to provide backtracking protection.
*/
static void _crng_backtrack_protect(struct crng_state *crng,
__u8 tmp[CHACHA20_BLOCK_SIZE], int used)
{
unsigned long flags;
__u32 *s, *d;
int i;
used = round_up(used, sizeof(__u32));
if (used + CHACHA20_KEY_SIZE > CHACHA20_BLOCK_SIZE) {
extract_crng(tmp);
used = 0;
}
spin_lock_irqsave(&crng->lock, flags);
s = (__u32 *) &tmp[used];
d = &crng->state[4];
for (i=0; i < 8; i++)
*d++ ^= *s++;
spin_unlock_irqrestore(&crng->lock, flags);
}
static void crng_backtrack_protect(__u8 tmp[CHACHA20_BLOCK_SIZE], int used)
{
struct crng_state *crng = NULL;
#ifdef CONFIG_NUMA
if (crng_node_pool)
crng = crng_node_pool[numa_node_id()];
if (crng == NULL)
#endif
crng = &primary_crng;
_crng_backtrack_protect(crng, tmp, used);
}
static ssize_t extract_crng_user(void __user *buf, size_t nbytes) static ssize_t extract_crng_user(void __user *buf, size_t nbytes)
{ {
ssize_t ret = 0, i; ssize_t ret = 0, i = CHACHA20_BLOCK_SIZE;
__u8 tmp[CHACHA20_BLOCK_SIZE]; __u8 tmp[CHACHA20_BLOCK_SIZE];
int large_request = (nbytes > 256); int large_request = (nbytes > 256);
@ -916,6 +957,7 @@ static ssize_t extract_crng_user(void __user *buf, size_t nbytes)
buf += i; buf += i;
ret += i; ret += i;
} }
crng_backtrack_protect(tmp, i);
/* Wipe data just written to memory */ /* Wipe data just written to memory */
memzero_explicit(tmp, sizeof(tmp)); memzero_explicit(tmp, sizeof(tmp));
@ -1473,8 +1515,10 @@ void get_random_bytes(void *buf, int nbytes)
if (nbytes > 0) { if (nbytes > 0) {
extract_crng(tmp); extract_crng(tmp);
memcpy(buf, tmp, nbytes); memcpy(buf, tmp, nbytes);
memzero_explicit(tmp, nbytes); crng_backtrack_protect(tmp, nbytes);
} } else
crng_backtrack_protect(tmp, CHACHA20_BLOCK_SIZE);
memzero_explicit(tmp, sizeof(tmp));
} }
EXPORT_SYMBOL(get_random_bytes); EXPORT_SYMBOL(get_random_bytes);