Re: [PATCH bpf v2] bpf: Fix use-after-free in offloaded map/prog info fill

[Daniel Borkmann]

On 4/9/26 4:37 AM, Jiayuan Chen wrote:
> When querying info for an offloaded BPF map or program,
> bpf_map_offload_info_fill_ns() and bpf_prog_offload_info_fill_ns()
> obtain the network namespace with get_net(dev_net(offmap->netdev)).
> However, the associated netdev's netns may be racing with teardown
> during netns destruction. If the netns refcount has already reached 0,
> get_net() performs a refcount_t increment on 0, triggering:
>
>    refcount_t: addition on 0; use-after-free.
>
> Although rtnl_lock and bpf_devs_lock ensure the netdev pointer remains
> valid, they cannot prevent the netns refcount from reaching zero.
>
> Fix this by using maybe_get_net() instead of get_net(). maybe_get_net()
> uses refcount_inc_not_zero() and returns NULL if the refcount is already
> zero, which causes ns_get_path_cb() to fail and the caller to return
> -ENOENT -- the correct behavior when the netns is being destroyed.
>
> Fixes: 675fc275a3a2d ("bpf: offload: report device information for offloaded programs")
> Fixes: 52775b33bb507 ("bpf: offload: report device information about offloaded maps")
> Reported-by: Yinhao Hu <dddddd@xxxxxxxxxxx>
> Reported-by: Kaiyan Mei <M202472210@xxxxxxxxxxx>
> Reviewed-by: Dongliang Mu <dzm91@xxxxxxxxxxx>
> Closes: https://lore.kernel.org/bpf/f0aa3678-79c9-47ae-9e8c-02a3d1df160a@xxxxxxxxxxx/
> Signed-off-by: Jiayuan Chen <jiayuan.chen@xxxxxxxxx>
> ---
> v1 -> v2: fix the commit message and simplify to ternary.
> v1: https://lore.kernel.org/bpf/20260408104732.259683-1-jiayuan.chen@xxxxxxxxx/
Acked-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>

(should go into bpf-next)