[PATCH] vhost: validate range size before adding to iotlb

Anirudh Rayabharam
2022-02-21T19:53:49Z

In vhost_iotlb_add_range_ctx(), validate the range size is non-zero
before proceeding with adding it to the iotlb.

Range size can overflow to 0 when start is 0 and last is (2^64 - 1).
One instance where it can happen is when userspace sends an IOTLB
message with iova=size=uaddr=0 (vhost_process_iotlb_msg). So, an
entry with size = 0, start = 0, last = (2^64 - 1) ends up in the
iotlb. Next time a packet is sent, iotlb_access_ok() loops
indefinitely due to that erroneous entry:

Call Trace:
<TASK>
iotlb_access_ok+0x21b/0x3e0 drivers/vhost/vhost.c:1340
vq_meta_prefetch+0xbc/0x280 drivers/vhost/vhost.c:1366
vhost_transport_do_send_pkt+0xe0/0xfd0 drivers/vhost/vsock.c:104
vhost_worker+0x23d/0x3d0 drivers/vhost/vhost.c:372
kthread+0x2e9/0x3a0 kernel/kthread.c:377
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
</TASK>

Reported by syzbot at:
https://syzkaller.appspot.com/bug?extid=0abd373e2e50d704db87

Reported-by: syzbot+0abd373e2e50d704db87@syzkaller.appspotmail.com
Tested-by: syzbot+0abd373e2e50d704db87@syzkaller.appspotmail.com
Signed-off-by: Anirudh Rayabharam <mail@anirudhrb.com>
---
drivers/vhost/iotlb.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/vhost/iotlb.c b/drivers/vhost/iotlb.c
index 670d56c879e5..b9de74bd2f9c 100644
--- a/drivers/vhost/iotlb.c
+++ b/drivers/vhost/iotlb.c
@@ -53,8 +53,10 @@ int vhost_iotlb_add_range_ctx(struct vhost_iotlb *iotlb,
void *opaque)
{
struct vhost_iotlb_map *map;
+ u64 size = last - start + 1;

- if (last < start)
+ // size can overflow to 0 when start is 0 and last is (2^64 - 1).
+ if (last < start || size == 0)
return -EFAULT;

if (iotlb->limit &&
@@ -69,7 +71,7 @@ int vhost_iotlb_add_range_ctx(struct vhost_iotlb *iotlb,
return -ENOMEM;

map->start = start;
- map->size = last - start + 1;
+ map->size = size;
map->last = last;
map->addr = addr;
map->perm = perm;
--
2.35.1