linux-kernel - [PATCH] vhost-vdpa: fix potential memory leak during the release

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Date:   Wed,  9 Nov 2022 16:42:13 +0100
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     virtualization@...ts.linux-foundation.org
Cc:     "Michael S. Tsirkin" <mst@...hat.com>, eperezma@...hat.com,
        netdev@...r.kernel.org, kvm@...r.kernel.org,
        Stefano Garzarella <sgarzare@...hat.com>,
        Gautam Dawar <gautam.dawar@...inx.com>,
        Jason Wang <jasowang@...hat.com>, linux-kernel@...r.kernel.org
Subject: [PATCH] vhost-vdpa: fix potential memory leak during the release

Before commit 3d5698793897 ("vhost-vdpa: introduce asid based IOTLB")
we call vhost_vdpa_iotlb_unmap(v, iotlb, 0ULL, 0ULL - 1) during the
release to free all the resources allocated when processing user IOTLB
messages through vhost_vdpa_process_iotlb_update().
That commit changed the handling of IOTLB a bit, and we accidentally
removed some code called during the release.

We partially fixed with commit 037d4305569a ("vhost-vdpa: call
vhost_vdpa_cleanup during the release") but a potential memory leak is
still there as showed by kmemleak if the application does not send
VHOST_IOTLB_INVALIDATE or crashes:

  unreferenced object 0xffff888007fbaa30 (size 16):
    comm "blkio-bench", pid 914, jiffies 4294993521 (age 885.500s)
    hex dump (first 16 bytes):
      40 73 41 07 80 88 ff ff 00 00 00 00 00 00 00 00  @sA.............
    backtrace:
      [<0000000087736d2a>] kmem_cache_alloc_trace+0x142/0x1c0
      [<0000000060740f50>] vhost_vdpa_process_iotlb_msg+0x68c/0x901 [vhost_vdpa]
      [<0000000083e8e205>] vhost_chr_write_iter+0xc0/0x4a0 [vhost]
      [<000000008f2f414a>] vhost_vdpa_chr_write_iter+0x18/0x20 [vhost_vdpa]
      [<00000000de1cd4a0>] vfs_write+0x216/0x4b0
      [<00000000a2850200>] ksys_write+0x71/0xf0
      [<00000000de8e720b>] __x64_sys_write+0x19/0x20
      [<0000000018b12cbb>] do_syscall_64+0x3f/0x90
      [<00000000986ec465>] entry_SYSCALL_64_after_hwframe+0x63/0xcd

Let's fix calling vhost_vdpa_iotlb_unmap() on the whole range in
vhost_vdpa_remove_as(). We move that call before vhost_dev_cleanup()
since we need a valid v->vdev.mm in vhost_vdpa_pa_unmap().
vhost_iotlb_reset() call can be removed, since vhost_vdpa_iotlb_unmap()
on the whole range removes all the entries.

The kmemleak log reported was observed with a vDPA device that has `use_va`
set to true (e.g. VDUSE). This patch has been tested with both types of
devices.

Fixes: 037d4305569a ("vhost-vdpa: call vhost_vdpa_cleanup during the release")
Fixes: 3d5698793897 ("vhost-vdpa: introduce asid based IOTLB")
Signed-off-by: Stefano Garzarella <sgarzare@...hat.com>
---
 drivers/vhost/vdpa.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
index 166044642fd5..b08e07fc7d1f 100644
--- a/drivers/vhost/vdpa.c
+++ b/drivers/vhost/vdpa.c
@@ -65,6 +65,10 @@ static DEFINE_IDA(vhost_vdpa_ida);
 
 static dev_t vhost_vdpa_major;
 
+static void vhost_vdpa_iotlb_unmap(struct vhost_vdpa *v,
+				   struct vhost_iotlb *iotlb,
+				   u64 start, u64 last);
+
 static inline u32 iotlb_to_asid(struct vhost_iotlb *iotlb)
 {
 	struct vhost_vdpa_as *as = container_of(iotlb, struct
@@ -135,7 +139,7 @@ static int vhost_vdpa_remove_as(struct vhost_vdpa *v, u32 asid)
 		return -EINVAL;
 
 	hlist_del(&as->hash_link);
-	vhost_iotlb_reset(&as->iotlb);
+	vhost_vdpa_iotlb_unmap(v, &as->iotlb, 0ULL, 0ULL - 1);
 	kfree(as);
 
 	return 0;
@@ -1162,14 +1166,14 @@ static void vhost_vdpa_cleanup(struct vhost_vdpa *v)
 	struct vhost_vdpa_as *as;
 	u32 asid;
 
-	vhost_dev_cleanup(&v->vdev);
-	kfree(v->vdev.vqs);
-
 	for (asid = 0; asid < v->vdpa->nas; asid++) {
 		as = asid_to_as(v, asid);
 		if (as)
 			vhost_vdpa_remove_as(v, asid);
 	}
+
+	vhost_dev_cleanup(&v->vdev);
+	kfree(v->vdev.vqs);
 }
 
 static int vhost_vdpa_open(struct inode *inode, struct file *filep)
-- 
2.38.1