Fix double fget() in vhost_net_set_backend()
stable inclusion from stable-v5.10.118 commit ec0d801d1a44d9259377142c6218885ecd685e41 category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I5L686 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ec0d801d1a44d9259377142c6218885ecd685e41 -------------------------------- commit fb4554c2 upstream. Descriptor table is a shared resource; two fget() on the same descriptor may return different struct file references. get_tap_ptr_ring() is called after we'd found (and pinned) the socket we'll be using and it tries to find the private tun/tap data structures associated with it. Redoing the lookup by the same file descriptor we'd used to get the socket is racy - we need to same struct file. Thanks to Jason for spotting a braino in the original variant of patch - I'd missed the use of fd == -1 for disabling backend, and in that case we can end up with sock == NULL and sock != oldsock. Cc: stable@kernel.org Acked-by: NMichael S. Tsirkin <mst@redhat.com> Signed-off-by: NJason Wang <jasowang@redhat.com> Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk> Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com> Acked-by: NXie XiuQi <xiexiuqi@huawei.com>
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