Re: bpf_redirect_map not working after tail call

Daniel Borkmann

On 06/04/2018 01:04 PM, Jesper Dangaard Brouer via iovisor-dev wrote:
On Fri, 1 Jun 2018 14:15:58 +0200
Sebastiano Miano via iovisor-dev <iovisor-dev@...> wrote:

Dear all,

We have noticed that the bpf_redirect_map returns an error when it is
called after a tail call.
The xdp_redirect_map program (under sample/bpf) works fine, but if we
modify it as shown in the following diff, it doesn't work anymore.
I have debugged it with the xdp_monitor application and the error
returned is EFAULT.
Is this a known issue? Am I doing something wrong?
Argh, this is likely an issue/bug due to the check xdp_map_invalid(),
that was introduced in commit 7c3001313396 ("bpf: fix ri->map_owner
pointer on bpf_prog_realloc").

To Daniel, I don't know how to solve this, could you give some advice?

static inline bool xdp_map_invalid(const struct bpf_prog *xdp_prog,
unsigned long aux)
return (unsigned long)xdp_prog->aux != aux;

static int xdp_do_redirect_map(struct net_device *dev, struct xdp_buff *xdp,
struct bpf_prog *xdp_prog)
struct redirect_info *ri = this_cpu_ptr(&redirect_info);
unsigned long map_owner = ri->map_owner;
struct bpf_map *map = ri->map;
u32 index = ri->ifindex;
void *fwd = NULL;
int err;

if (unlikely(xdp_map_invalid(xdp_prog, map_owner))) {
err = -EFAULT;
map = NULL;
goto err;
Argh, I see the issue. Working on a fix after checking the syzkaller reports.

Thanks for the report!

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