Re: [PATCH net] tun: Remove nested call to bpf_net_ctx_set() in do_xdp_generic()

Jeongjun Park wrote:

In the previous commit, bpf_net_context handling was added to 
tun_sendmsg() and do_xdp_generic(), but if you write code like this,
bpf_net_context overlaps in the call trace below, causing various
memory corruptions.

I'm no expert on this code, but commit 401cb7dae813 that introduced
bpf_net_ctx_set explicitly states that nested calls are allowed.

And the function does imply that:

static inline struct bpf_net_context *bpf_net_ctx_set(struct bpf_net_context *bpf_net_ctx)
{
        struct task_struct *tsk = current;

        if (tsk->bpf_net_context != NULL)
                return NULL;
        bpf_net_ctx->ri.kern_flags = 0;

        tsk->bpf_net_context = bpf_net_ctx;
        return bpf_net_ctx;
}


 

<Call trace>
...
tun_sendmsg() // bpf_net_ctx_set()
  tun_xdp_one()
    do_xdp_generic() // bpf_net_ctx_set() <-- nested
...

This patch removes the bpf_net_context handling that exists in 
do_xdp_generic() and modifies it to handle it in the parent function.

Is tun_xdp_one missing? That also calls do_xdp_generic.