Re: [bpf-next, v2] bpf: verifier: Fix potential memleak and UAF in bpf verifier

[Song Liu]

On Wed, Jul 14, 2021 at 2:33 AM He Fengqing <hefengqing@xxxxxxxxxx> wrote:
>
> In bpf_patch_insn_data(), we first use the bpf_patch_insn_single() to
> insert new instructions, then use adjust_insn_aux_data() to adjust
> insn_aux_data. If the old env->prog have no enough room for new inserted
> instructions, we use bpf_prog_realloc to construct new_prog and free the
> old env->prog.
>
> There have two errors here. First, if adjust_insn_aux_data() return
> ENOMEM, we should free the new_prog. Second, if adjust_insn_aux_data()
> return ENOMEM, bpf_patch_insn_data() will return NULL, and env->prog has
> been freed in bpf_prog_realloc, but we will use it in bpf_check().
>
> So in this patch, we make the adjust_insn_aux_data() never fails. In
> bpf_patch_insn_data(), we first pre-malloc memory for the new
> insn_aux_data, then call bpf_patch_insn_single() to insert new
> instructions, at last call adjust_insn_aux_data() to adjust
> insn_aux_data.
>
> Fixes: 8041902dae52 ("bpf: adjust insn_aux_data when patching insns")
>
> Signed-off-by: He Fengqing <hefengqing@xxxxxxxxxx>

Acked-by: Song Liu <songliubraving@xxxxxx>

with one nitpick below.

>
>   v1->v2:
>     pre-malloc memory for new insn_aux_data first, then
>     adjust_insn_aux_data() will never fails.
> ---
>  kernel/bpf/verifier.c | 30 +++++++++++++++++++-----------
>  1 file changed, 19 insertions(+), 11 deletions(-)
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index be38bb930bf1..07cf791510f1 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -11425,10 +11425,11 @@ static void convert_pseudo_ld_imm64(struct bpf_verifier_env *env)
>   * insni[off, off + cnt).  Adjust corresponding insn_aux_data by copying
>   * [0, off) and [off, end) to new locations, so the patched range stays zero
>   */
> -static int adjust_insn_aux_data(struct bpf_verifier_env *env,
> -                               struct bpf_prog *new_prog, u32 off, u32 cnt)
> +static void adjust_insn_aux_data(struct bpf_verifier_env *env,
> +                                struct bpf_insn_aux_data *new_data,
> +                                struct bpf_prog *new_prog, u32 off, u32 cnt)
>  {
> -       struct bpf_insn_aux_data *new_data, *old_data = env->insn_aux_data;
> +       struct bpf_insn_aux_data *old_data = env->insn_aux_data;
>         struct bpf_insn *insn = new_prog->insnsi;
>         u32 old_seen = old_data[off].seen;
>         u32 prog_len;
> @@ -11441,12 +11442,9 @@ static int adjust_insn_aux_data(struct bpf_verifier_env *env,
>         old_data[off].zext_dst = insn_has_def32(env, insn + off + cnt - 1);
>
>         if (cnt == 1)
> -               return 0;
> +               return;
>         prog_len = new_prog->len;
> -       new_data = vzalloc(array_size(prog_len,
> -                                     sizeof(struct bpf_insn_aux_data)));
> -       if (!new_data)
> -               return -ENOMEM;
> +
>         memcpy(new_data, old_data, sizeof(struct bpf_insn_aux_data) * off);
>         memcpy(new_data + off + cnt - 1, old_data + off,
>                sizeof(struct bpf_insn_aux_data) * (prog_len - off - cnt + 1));
> @@ -11457,7 +11455,7 @@ static int adjust_insn_aux_data(struct bpf_verifier_env *env,
>         }
>         env->insn_aux_data = new_data;
>         vfree(old_data);
> -       return 0;
> +       return;
No need to say return here.

>  }
>
>  static void adjust_subprog_starts(struct bpf_verifier_env *env, u32 off, u32 len)
> @@ -11492,6 +11490,14 @@ static struct bpf_prog *bpf_patch_insn_data(struct bpf_verifier_env *env, u32 of
>                                             const struct bpf_insn *patch, u32 len)
>  {
>         struct bpf_prog *new_prog;
> +       struct bpf_insn_aux_data *new_data = NULL;
> +
> +       if (len > 1) {
> +               new_data = vzalloc(array_size(env->prog->len + len - 1,
> +                                             sizeof(struct bpf_insn_aux_data)));
> +               if (!new_data)
> +                       return NULL;
> +       }
>
>         new_prog = bpf_patch_insn_single(env->prog, off, patch, len);
>         if (IS_ERR(new_prog)) {
> @@ -11499,10 +11505,12 @@ static struct bpf_prog *bpf_patch_insn_data(struct bpf_verifier_env *env, u32 of
>                         verbose(env,
>                                 "insn %d cannot be patched due to 16-bit range\n",
>                                 env->insn_aux_data[off].orig_idx);
> +               if (new_data)
> +                       vfree(new_data);
> +
>                 return NULL;
>         }
> -       if (adjust_insn_aux_data(env, new_prog, off, len))
> -               return NULL;
> +       adjust_insn_aux_data(env, new_data, new_prog, off, len);
>         adjust_subprog_starts(env, off, len);
>         adjust_poke_descs(new_prog, off, len);
>         return new_prog;
> --
> 2.25.1
>