3.16.79-rc1 review patch. If anyone has any objections, please let me know.
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From: Laurent Vivier lvivier@redhat.com
commit 78887832e76541f77169a24ac238fccb51059b63 upstream.
add_early_randomness() is called by hwrng_register() when the hardware is added. If this hardware and its module are present at boot, and if there is no data available the boot hangs until data are available and can't be interrupted.
For instance, in the case of virtio-rng, in some cases the host can be not able to provide enough entropy for all the guests.
We can have two easy ways to reproduce the problem but they rely on misconfiguration of the hypervisor or the egd daemon:
- if virtio-rng device is configured to connect to the egd daemon of the host but when the virtio-rng driver asks for data the daemon is not connected,
- if virtio-rng device is configured to connect to the egd daemon of the host but the egd daemon doesn't provide data.
The guest kernel will hang at boot until the virtio-rng driver provides enough data.
To avoid that, call rng_get_data() in non-blocking mode (wait=0) from add_early_randomness().
Signed-off-by: Laurent Vivier lvivier@redhat.com Fixes: d9e797261933 ("hwrng: add randomness to system from rng...") Reviewed-by: Theodore Ts'o tytso@mit.edu 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 | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/drivers/char/hw_random/core.c +++ b/drivers/char/hw_random/core.c @@ -68,7 +68,7 @@ static void add_early_randomness(struct int bytes_read; size_t size = min_t(size_t, 16, rng_buffer_size());
- bytes_read = rng_get_data(rng, rng_buffer, size, 1); + bytes_read = rng_get_data(rng, rng_buffer, size, 0); if (bytes_read > 0) add_device_randomness(rng_buffer, bytes_read); }