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SubjectRe: /dev/urandom uses uninit bytes, leaks user data
Date
John Reiser <jreiser@bitwagon.com> wrote:
>
> If speed matters that much, then please recoup 33 cycles on x86
> by using shifts instead of three divides, such as (gcc 4.1.2):
>
> add_entropy_words(r, tmp, (bytes + 3) / 4);
>
> 0x8140689 <xfer_secondary_pool+206>: lea 0x3(%esi),%eax
> 0x814068c <xfer_secondary_pool+209>: mov $0x4,%dl
> 0x814068e <xfer_secondary_pool+211>: mov %edx,%edi
> 0x8140690 <xfer_secondary_pool+213>: cltd
> 0x8140691 <xfer_secondary_pool+214>: idiv %edi

There ought to be a warning about this sort of thing.

[CHAR] random: Avoid signed integer division

Joihn Reiser pointed out that we use signed integer divisions
unnecessarily in random.c. This is bad because the C compiler
is obliged to consider the case of a negative dividend.

This patch changes all the relevant divisions and modulus operations
to use unsigned arithmetic.

Signed-off: Herbert Xu <herbert@gondor.apana.org.au>

Thanks,
--
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
--
diff --git a/drivers/char/random.c b/drivers/char/random.c
index 5fee056..6c70bfb 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -694,11 +694,11 @@ static void xfer_secondary_pool(struct entropy_store *r, size_t nbytes)
if (r->pull && r->entropy_count < nbytes * 8 &&
r->entropy_count < r->poolinfo->POOLBITS) {
/* If we're limited, always leave two wakeup worth's BITS */
- int rsvd = r->limit ? 0 : random_read_wakeup_thresh/4;
+ int rsvd = r->limit ? 0 : random_read_wakeup_thresh / 4u;
int bytes = nbytes;

/* pull at least as many as BYTES as wakeup BITS */
- bytes = max_t(int, bytes, random_read_wakeup_thresh / 8);
+ bytes = max_t(int, bytes, random_read_wakeup_thresh / 8u);
/* but never more than the buffer size */
bytes = min_t(int, bytes, sizeof(tmp));

@@ -707,8 +707,8 @@ static void xfer_secondary_pool(struct entropy_store *r, size_t nbytes)
r->name, bytes * 8, nbytes * 8, r->entropy_count);

bytes=extract_entropy(r->pull, tmp, bytes,
- random_read_wakeup_thresh / 8, rsvd);
- add_entropy_words(r, tmp, (bytes + 3) / 4);
+ random_read_wakeup_thresh / 8u, rsvd);
+ add_entropy_words(r, tmp, (bytes + 3) / 4u);
credit_entropy_store(r, bytes*8);
}
}
@@ -739,14 +739,14 @@ static size_t account(struct entropy_store *r, size_t nbytes, int min,
nbytes * 8, r->name);

/* Can we pull enough? */
- if (r->entropy_count / 8 < min + reserved) {
+ if (r->entropy_count / 8u < min + reserved) {
nbytes = 0;
} else {
/* If limited, never pull more than available */
- if (r->limit && nbytes + reserved >= r->entropy_count / 8)
- nbytes = r->entropy_count/8 - reserved;
+ if (r->limit && nbytes + reserved >= r->entropy_count / 8u)
+ nbytes = r->entropy_count / 8u - reserved;

- if(r->entropy_count / 8 >= nbytes + reserved)
+ if(r->entropy_count / 8u >= nbytes + reserved)
r->entropy_count -= nbytes*8;
else
r->entropy_count = reserved;
@@ -781,7 +781,7 @@ static void extract_buf(struct entropy_store *r, __u8 *out)
/* hash blocks of 16 words = 512 bits */
sha_transform(buf, (__u8 *)(r->pool + i), buf + 5);
/* feed back portion of the resulting hash */
- add_entropy_words(r, &buf[i % 5], 1);
+ add_entropy_words(r, &buf[i % 5u], 1);
}

/*
@@ -789,7 +789,7 @@ static void extract_buf(struct entropy_store *r, __u8 *out)
* portion of the pool while mixing, and hash one
* final time.
*/
- __add_entropy_words(r, &buf[i % 5], 1, data);
+ __add_entropy_words(r, &buf[i % 5u], 1, data);
sha_transform(buf, (__u8 *)data, buf + 5);

/*
@@ -1040,7 +1040,7 @@ write_pool(struct entropy_store *r, const char __user *buffer, size_t count)
count -= bytes;
p += bytes;

- add_entropy_words(r, buf, (bytes + 3) / 4);
+ add_entropy_words(r, buf, (bytes + 3) / 4u);
}

return 0;

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