3.16.74-rc1 review patch. If anyone has any objections, please let me know.
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From: yongduan yongduan@tencent.com
commit 060423bfdee3f8bc6e2c1bac97de24d5415e2bc4 upstream.
The code assumes log_num < in_num everywhere, and that is true as long as in_num is incremented by descriptor iov count, and log_num by 1. However this breaks if there's a zero sized descriptor.
As a result, if a malicious guest creates a vring desc with desc.len = 0, it may cause the host kernel to crash by overflowing the log array. This bug can be triggered during the VM migration.
There's no need to log when desc.len = 0, so just don't increment log_num in this case.
Fixes: 3a4d5c94e959 ("vhost_net: a kernel-level virtio server") Reviewed-by: Lidong Chen lidongchen@tencent.com Signed-off-by: ruippan ruippan@tencent.com Signed-off-by: yongduan yongduan@tencent.com Acked-by: Michael S. Tsirkin mst@redhat.com Reviewed-by: Tyler Hicks tyhicks@canonical.com Signed-off-by: Michael S. Tsirkin mst@redhat.com [bwh: Backported to 3.16: adjust context] Signed-off-by: Ben Hutchings ben@decadent.org.uk --- drivers/vhost/vhost.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
--- a/drivers/vhost/vhost.c +++ b/drivers/vhost/vhost.c @@ -1194,7 +1194,7 @@ static int get_indirect(struct vhost_vir /* If this is an input descriptor, increment that count. */ if (desc.flags & VRING_DESC_F_WRITE) { *in_num += ret; - if (unlikely(log)) { + if (unlikely(log && ret)) { log[*log_num].addr = desc.addr; log[*log_num].len = desc.len; ++*log_num; @@ -1317,7 +1317,7 @@ int vhost_get_vq_desc(struct vhost_virtq /* If this is an input descriptor, * increment that count. */ *in_num += ret; - if (unlikely(log)) { + if (unlikely(log && ret)) { log[*log_num].addr = desc.addr; log[*log_num].len = desc.len; ++*log_num;