On Sun, Jul 4, 2021 at 7:19 AM Alexei Starovoitov
<alexei.starovoitov@xxxxxxxxx> wrote:
> > > + struct bpf_insn ld_addrs[2] = {
> > > + BPF_LD_IMM64(BPF_REG_3, (long)prog),
> > The "prog" pointer value is used here.
> >
> > > + };
> > > +
> > > + insn_buf[0] = ld_addrs[0];
> > > + insn_buf[1] = ld_addrs[1];
> > > + insn_buf[2] = *insn;
> > > + cnt = 3;
> > > +
> > > + new_prog = bpf_patch_insn_data(env, i + delta, insn_buf, cnt);
> > > + if (!new_prog)
> > > + return -ENOMEM;
> > > +
> > > + delta += cnt - 1;
> > > + env->prog = prog = new_prog;
> > After bpf_patch_insn_data(), a new prog may be allocated.
> > Is the above old "prog" pointer value updated accordingly?
> > I could have missed something.
>
> excellent catch. The patching of prog can go bad either here
> or later if patching of some other insn happened to change prog.
> I'll try to switch to dynamic prog fetching via ksym.
> The timers won't work in the interpreted mode though.
> But that's better trade-off than link-list of insns to patch with a prog
> after all of bpf_patch_insn_data are done?
> Some other way to fix this issue?
fyi we've discussed it with Martin offline and he came up with an excellent idea
to patch prog->aux instead of prog here. I'll add that to a respin.
