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

Reported-by: Matt Mullins <mmull...@mmlx.us>
Tested-by: Matt Mullins <mmull...@mmlx.us>
Fixes: d3cc7996473a ("hwrng: fetch randomness only after device init")
Signed-off-by: Andy Lutomirski <l...@kernel.org>

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());
-       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 void cleanup_rng(struct kref *kref)

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