Linux 4.14.111

[thirdparty/kernel/stable-queue.git] / releases / 4.14.111 / hwrng-virtio-avoid-repeated-init-of-completion.patch

diff --git a/releases/4.14.111/hwrng-virtio-avoid-repeated-init-of-completion.patch b/releases/4.14.111/hwrng-virtio-avoid-repeated-init-of-completion.patch
new file mode 100644 (file)
index 0000000..feb7ceb
--- /dev/null
+++ b/releases/4.14.111/hwrng-virtio-avoid-repeated-init-of-completion.patch
@@ -0,0 +1,57 @@
+From 9dc0cd5d2e630d9701e157fbfc939727514be3a4 Mon Sep 17 00:00:00 2001
+From: David Tolnay <dtolnay@gmail.com>
+Date: Mon, 7 Jan 2019 14:36:11 -0800
+Subject: 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>
+---
+ drivers/char/hw_random/virtio-rng.c | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/drivers/char/hw_random/virtio-rng.c b/drivers/char/hw_random/virtio-rng.c
+index 3fa2f8a009b3..1c5c4314c6b5 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);
+       }
+ 
+-- 
+2.19.1
+