[PATCH 3.16 141/306] hwrng: core - Don't use a stack buffer in add_early_randomness()

Ben Hutchings
2017-02-15T23:23:41Z

From: Andrew Lutomirski <luto@kernel.org>

commit 6d4952d9d9d4dc2bb9c0255d95a09405a1e958f7 upstream.

hw_random carefully avoids using a stack buffer except in
add_early_randomness(). This causes a crash in virtio_rng if
CONFIG_VMAP_STACK=y.

Reported-by: Matt Mullins <mmullins@mmlx.us>
Tested-by: Matt Mullins <mmullins@mmlx.us>
Fixes: d3cc7996473a ("hwrng: fetch randomness only after device init")
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
drivers/char/hw_random/core.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

--- a/drivers/char/hw_random/core.c
+++ b/drivers/char/hw_random/core.c
@@ -65,12 +65,12 @@ static size_t rng_buffer_size(void)

static void add_early_randomness(struct hwrng *rng)
{
- unsigned char bytes[16];
int bytes_read;
+ size_t size = min_t(size_t, 16, rng_buffer_size());

- bytes_read = rng_get_data(rng, bytes, sizeof(bytes), 1);
+ bytes_read = rng_get_data(rng, rng_buffer, size, 1);
if (bytes_read > 0)
- add_device_randomness(bytes, bytes_read);
+ add_device_randomness(rng_buffer, bytes_read);
}

static inline int hwrng_init(struct hwrng *rng)