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author | David Tolnay <dtolnay@gmail.com> | 2019-01-08 01:36:11 +0300 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2019-04-05 23:33:14 +0300 |
commit | a3aa9d93b9ab68ca76956f2425805ede49d125cd (patch) | |
tree | 1c13f0c527608b4f8e235ffd58f5736624960392 /drivers/char/hw_random | |
parent | 7aaa76e8a6abc787ffd8f40f39bf406762090641 (diff) | |
download | linux-a3aa9d93b9ab68ca76956f2425805ede49d125cd.tar.xz |
hwrng: virtio - Avoid repeated init of completion
[ Upstream commit aef027db48da56b6f25d0e54c07c8401ada6ce21 ]
The virtio-rng driver uses a completion called have_data to wait for a
virtio read to be fulfilled by the hypervisor. The completion is reset
before placing a buffer on the virtio queue and completed by the virtio
callback once data has been written into the buffer.
Prior to this commit, the driver called init_completion on this
completion both during probe as well as when registering virtio buffers
as part of a hwrng read operation. The second of these init_completion
calls should instead be reinit_completion because the have_data
completion has already been inited by probe. As described in
Documentation/scheduler/completion.txt, "Calling init_completion() twice
on the same completion object is most likely a bug".
This bug was present in the initial implementation of virtio-rng in
f7f510ec1957 ("virtio: An entropy device, as suggested by hpa"). Back
then the have_data completion was a single static completion rather than
a member of one of potentially multiple virtrng_info structs as
implemented later by 08e53fbdb85c ("virtio-rng: support multiple
virtio-rng devices"). The original driver incorrectly used
init_completion rather than INIT_COMPLETION to reset have_data during
read.
Tested by running `head -c48 /dev/random | hexdump` within crosvm, the
Chrome OS virtual machine monitor, and confirming that the virtio-rng
driver successfully produces random bytes from the host.
Signed-off-by: David Tolnay <dtolnay@gmail.com>
Tested-by: David Tolnay <dtolnay@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Diffstat (limited to 'drivers/char/hw_random')
-rw-r--r-- | drivers/char/hw_random/virtio-rng.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/drivers/char/hw_random/virtio-rng.c b/drivers/char/hw_random/virtio-rng.c index b89df66ea1ae..7abd604e938c 100644 --- a/drivers/char/hw_random/virtio-rng.c +++ b/drivers/char/hw_random/virtio-rng.c @@ -73,7 +73,7 @@ static int virtio_read(struct hwrng *rng, void *buf, size_t size, bool wait) if (!vi->busy) { vi->busy = true; - init_completion(&vi->have_data); + reinit_completion(&vi->have_data); register_buffer(vi, buf, size); } |