[PATCH 5.16 017/121] vhost: fix hung thread due to erroneous iotlb entries

Greg Kroah-Hartman
2022-03-14T12:26:25Z

From: Anirudh Rayabharam <mail@anirudhrb.com>

[ Upstream commit e2ae38cf3d91837a493cb2093c87700ff3cbe667 ]

In vhost_iotlb_add_range_ctx(), range size can overflow to 0 when
start is 0 and last is ULONG_MAX. 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 = ULONG_MAX 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

To fix this, do two things:

1. Return -EINVAL in vhost_chr_write_iter() when userspace asks to map
a range with size 0.
2. Fix vhost_iotlb_add_range_ctx() to handle the range [0, ULONG_MAX]
by splitting it into two entries.

Fixes: 0bbe30668d89e ("vhost: factor out IOTLB")
Reported-by: syzbot+0abd373e2e50d704db87@syzkaller.appspotmail.com
Tested-by: syzbot+0abd373e2e50d704db87@syzkaller.appspotmail.com
Signed-off-by: Anirudh Rayabharam <mail@anirudhrb.com>
Link: https://lore.kernel.org/r/20220305095525.5145-1-mail@anirudhrb.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/vhost/iotlb.c | 11 +++++++++++
drivers/vhost/vhost.c | 5 +++++
2 files changed, 16 insertions(+)

diff --git a/drivers/vhost/iotlb.c b/drivers/vhost/iotlb.c
index 670d56c879e5..40b098320b2a 100644
--- a/drivers/vhost/iotlb.c
+++ b/drivers/vhost/iotlb.c
@@ -57,6 +57,17 @@ int vhost_iotlb_add_range_ctx(struct vhost_iotlb *iotlb,
if (last < start)
return -EFAULT;

+ /* If the range being mapped is [0, ULONG_MAX], split it into two entries
+ * otherwise its size would overflow u64.
+ */
+ if (start == 0 && last == ULONG_MAX) {
+ u64 mid = last / 2;
+
+ vhost_iotlb_add_range_ctx(iotlb, start, mid, addr, perm, opaque);
+ addr += mid + 1;
+ start = mid + 1;
+ }
+
if (iotlb->limit &&
iotlb->nmaps == iotlb->limit &&
iotlb->flags & VHOST_IOTLB_FLAG_RETIRE) {
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 59edb5a1ffe2..55475fd59fb7 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -1170,6 +1170,11 @@ ssize_t vhost_chr_write_iter(struct vhost_dev *dev,
goto done;
}

+ if (msg.size == 0) {
+ ret = -EINVAL;
+ goto done;
+ }
+
if (dev->msg_handler)
ret = dev->msg_handler(dev, &msg);
else
--
2.34.1