[PATCH] vduse: validate virtqueue alignment

[Jia Jia <physicalmtea@gmail.com>]

vduse_validate_config() only checks the upper bound of vq_align. Invalid
values can therefore reach vring_create_virtqueue_map(). The split-ring
helpers use align - 1 as a bit mask, so the alignment must be a non-zero
power of two. A zero value makes vring_size() drop the descriptor and
available-ring part and vring_init() leave the used ring pointer NULL.

The VIRTIO spec requires the used ring to start at an address
aligned to at least 4 bytes. Reject values below VRING_USED_ALIGN_SIZE as
well as non-power-of-two values before they reach the virtio ring helpers.

Opening a virtio-net device created with vq_align=0 triggered:

BUG: KASAN: null-ptr-deref in virtqueue_kick_prepare_split+0xe3/0x100
Read of size 2 at addr 0000000000000000 by task systemd-network/1062

Call Trace (relevant frames):
 dump_stack_lvl
 print_report
 kasan_report
 __asan_load2
 virtqueue_kick_prepare_split+0xe3/0x100
 virtqueue_kick_prepare+0x40/0x60
 try_fill_recv+0x857/0x1250
 virtnet_open+0x189/0x460
 __dev_open+0x225/0x390
 __dev_change_flags+0x368/0x3b0
 netif_change_flags+0x56/0xc0
 do_setlink.isra.0+0x68c/0x1e30

Validate the value before it reaches the virtio ring helpers.

Fixes: c8a6153b6c59 ("vduse: Introduce VDUSE - vDPA Device in Userspace")
Signed-off-by: Jia Jia <physicalmtea@gmail.com>
---
 drivers/vdpa/vdpa_user/vduse_dev.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vduse_dev.c
--- a/drivers/vdpa/vdpa_user/vduse_dev.c
+++ b/drivers/vdpa/vdpa_user/vduse_dev.c
@@ -2190,7 +2190,9 @@ static bool vduse_validate_config(struct vduse_dev_config *config,
 			return false;
 	}
 
-	if (config->vq_align > PAGE_SIZE)
+	if (config->vq_align < VRING_USED_ALIGN_SIZE ||
+	    !is_power_of_2(config->vq_align) ||
+	    config->vq_align > PAGE_SIZE)
 		return false;
 
 	if (config->config_size > PAGE_SIZE)