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Subject[PATCH 5.10 021/157] vhost-vdpa: fix use-after-free of v->config_ctx
Date
From: Stefano Garzarella <sgarzare@redhat.com>

commit f6bbf0010ba004f5e90c7aefdebc0ee4bd3283b9 upstream.

When the 'v->config_ctx' eventfd_ctx reference is released we didn't
set it to NULL. So if the same character device (e.g. /dev/vhost-vdpa-0)
is re-opened, the 'v->config_ctx' is invalid and calling again
vhost_vdpa_config_put() causes use-after-free issues like the
following refcount_t underflow:

refcount_t: underflow; use-after-free.
WARNING: CPU: 2 PID: 872 at lib/refcount.c:28 refcount_warn_saturate+0xae/0xf0
RIP: 0010:refcount_warn_saturate+0xae/0xf0
Call Trace:
eventfd_ctx_put+0x5b/0x70
vhost_vdpa_release+0xcd/0x150 [vhost_vdpa]
__fput+0x8e/0x240
____fput+0xe/0x10
task_work_run+0x66/0xa0
exit_to_user_mode_prepare+0x118/0x120
syscall_exit_to_user_mode+0x21/0x50
? __x64_sys_close+0x12/0x40
do_syscall_64+0x45/0x50
entry_SYSCALL_64_after_hwframe+0x44/0xae

Fixes: 776f395004d8 ("vhost_vdpa: Support config interrupt in vdpa")
Cc: lingshan.zhu@intel.com
Cc: stable@vger.kernel.org
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Link: https://lore.kernel.org/r/20210311135257.109460-2-sgarzare@redhat.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Zhu Lingshan <lingshan.zhu@intel.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/vhost/vdpa.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

--- a/drivers/vhost/vdpa.c
+++ b/drivers/vhost/vdpa.c
@@ -312,8 +312,10 @@ static long vhost_vdpa_get_vring_num(str

static void vhost_vdpa_config_put(struct vhost_vdpa *v)
{
- if (v->config_ctx)
+ if (v->config_ctx) {
eventfd_ctx_put(v->config_ctx);
+ v->config_ctx = NULL;
+ }
}

static long vhost_vdpa_set_config_call(struct vhost_vdpa *v, u32 __user *argp)

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