From: Herbert Xu <herbert@gondor.apana.org.au> stable inclusion from stable-v4.19.291 commit 241ef15776a7c8505008db689175b320d345ecd3 category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/12776 CVE: CVE-2023-53998 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=... -------------------------------- [ Upstream commit ac52578d6e8d300dd50f790f29a24169b1edd26c ] The virtio rng device kicks off a new entropy request whenever the data available reaches zero. When a new request occurs at the end of a read operation, that is, when the result of that request is only needed by the next reader, then there is a race between the writing of the new data and the next reader. This is because there is no synchronisation whatsoever between the writer and the reader. Fix this by writing data_avail with smp_store_release and reading it with smp_load_acquire when we first enter read. The subsequent reads are safe because they're either protected by the first load acquire, or by the completion mechanism. Also remove the redundant zeroing of data_idx in random_recv_done (data_idx must already be zero at this point) and data_avail in request_entropy (ditto). Reported-by: syzbot+726dc8c62c3536431ceb@syzkaller.appspotmail.com Fixes: f7f510ec1957 ("virtio: An entropy device, as suggested by hpa.") Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au> Acked-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au> Signed-off-by: Sasha Levin <sashal@kernel.org> Signed-off-by: Pu Lehui <pulehui@huawei.com> --- drivers/char/hw_random/virtio-rng.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) diff --git a/drivers/char/hw_random/virtio-rng.c b/drivers/char/hw_random/virtio-rng.c index a84248c26fd7..58884d875201 100644 --- a/drivers/char/hw_random/virtio-rng.c +++ b/drivers/char/hw_random/virtio-rng.c @@ -17,6 +17,7 @@ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA */ +#include <asm/barrier.h> #include <linux/err.h> #include <linux/hw_random.h> #include <linux/scatterlist.h> @@ -49,13 +50,13 @@ struct virtrng_info { static void random_recv_done(struct virtqueue *vq) { struct virtrng_info *vi = vq->vdev->priv; + unsigned int len; /* We can get spurious callbacks, e.g. shared IRQs + virtio_pci. */ - if (!virtqueue_get_buf(vi->vq, &vi->data_avail)) + if (!virtqueue_get_buf(vi->vq, &len)) return; - vi->data_idx = 0; - + smp_store_release(&vi->data_avail, len); complete(&vi->have_data); } @@ -64,7 +65,6 @@ static void request_entropy(struct virtrng_info *vi) struct scatterlist sg; reinit_completion(&vi->have_data); - vi->data_avail = 0; vi->data_idx = 0; sg_init_one(&sg, vi->data, sizeof(vi->data)); @@ -100,7 +100,7 @@ static int virtio_read(struct hwrng *rng, void *buf, size_t size, bool wait) read = 0; /* copy available data */ - if (vi->data_avail) { + if (smp_load_acquire(&vi->data_avail)) { chunk = copy_data(vi, buf, size); size -= chunk; read += chunk; -- 2.34.1