From patchwork Mon Oct 17 17:06:27 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: [resend, 4.9] hw_random: Don't use a stack buffer in add_early_randomness() From: Andrew Lutomirski X-Patchwork-Id: 9380037 Message-Id: <4169224b6858d1cf149f1a73f8a03603fa19076d.1476638125.git.luto@kernel.org> To: linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org, Matt Mackall , Herbert Xu , Rusty Russell Cc: Jens Axboe , Matt Mullins , Andy Lutomirski Date: Mon, 17 Oct 2016 10:06:27 -0700 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 Tested-by: Matt Mullins Fixes: d3cc7996473a ("hwrng: fetch randomness only after device init") Signed-off-by: Andy Lutomirski --- This fixes a crash in 4.9-rc1. resending because I typoed the git send-email command. I stealthily added Matt's Tested-by, too. drivers/char/hw_random/core.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c index 9203f2d130c0..340f96e44642 100644 --- a/drivers/char/hw_random/core.c +++ b/drivers/char/hw_random/core.c @@ -84,14 +84,14 @@ 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()); mutex_lock(&reading_mutex); - bytes_read = rng_get_data(rng, bytes, sizeof(bytes), 1); + bytes_read = rng_get_data(rng, rng_buffer, size, 1); mutex_unlock(&reading_mutex); if (bytes_read > 0) - add_device_randomness(bytes, bytes_read); + add_device_randomness(rng_buffer, bytes_read); } static inline void cleanup_rng(struct kref *kref)