netdev - Re: [PATCH net v2] bpf: Fix memory leaks in __check_func

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Date:   Wed, 2 Nov 2022 12:05:18 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Wang Yufen <wangyufen@...wei.com>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org, ast@...nel.org,
        daniel@...earbox.net, john.fastabend@...il.com, andrii@...nel.org,
        martin.lau@...ux.dev, yhs@...com, joe@...d.net.nz
Subject: Re: [PATCH net v2] bpf: Fix memory leaks in __check_func_call

On Thu, Oct 27, 2022 at 10:01 PM Wang Yufen <wangyufen@...wei.com> wrote:
>
> kmemleak reports this issue:
>
> unreferenced object 0xffff88817139d000 (size 2048):
>   comm "test_progs", pid 33246, jiffies 4307381979 (age 45851.820s)
>   hex dump (first 32 bytes):
>     01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>   backtrace:
>     [<0000000045f075f0>] kmalloc_trace+0x27/0xa0
>     [<0000000098b7c90a>] __check_func_call+0x316/0x1230
>     [<00000000b4c3c403>] check_helper_call+0x172e/0x4700
>     [<00000000aa3875b7>] do_check+0x21d8/0x45e0
>     [<000000001147357b>] do_check_common+0x767/0xaf0
>     [<00000000b5a595b4>] bpf_check+0x43e3/0x5bc0
>     [<0000000011e391b1>] bpf_prog_load+0xf26/0x1940
>     [<0000000007f765c0>] __sys_bpf+0xd2c/0x3650
>     [<00000000839815d6>] __x64_sys_bpf+0x75/0xc0
>     [<00000000946ee250>] do_syscall_64+0x3b/0x90
>     [<0000000000506b7f>] entry_SYSCALL_64_after_hwframe+0x63/0xcd
>
> The root case here is: In function prepare_func_exit(), the callee is
> not released in the abnormal scenario after "state->curframe--;". To
> fix, move "state->curframe--;" to the very bottom of the function,
> right when we free callee and reset frame[] pointer to NULL, as Andrii
> suggested.
>
> In addition, function __check_func_call() has a similar problem. In
> the abnormal scenario before "state->curframe++;", the callee is alse
> not released.
>
> Fixes: 69c087ba6225 ("bpf: Add bpf_for_each_map_elem() helper")
> Fixes: fd978bf7fd31 ("bpf: Add reference tracking to verifier")
> Signed-off-by: Wang Yufen <wangyufen@...wei.com>
> ---

This change seems to be breaking BPF selftests quite badly, please
check what's going on ([0]):

  [0] https://github.com/kernel-patches/bpf/actions/runs/3379444311/jobs/5611599540

>  kernel/bpf/verifier.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 014ee09..d28d460 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -6736,11 +6736,11 @@ static int __check_func_call(struct bpf_verifier_env *env, struct bpf_insn *insn
>         /* Transfer references to the callee */
>         err = copy_reference_state(callee, caller);
>         if (err)
> -               return err;
> +               goto err_out;
>
>         err = set_callee_state_cb(env, caller, callee, *insn_idx);
>         if (err)
> -               return err;
> +               goto err_out;
>
>         clear_caller_saved_regs(env, caller->regs);
>
> @@ -6757,6 +6757,11 @@ static int __check_func_call(struct bpf_verifier_env *env, struct bpf_insn *insn
>                 print_verifier_state(env, callee, true);
>         }
>         return 0;
> +
> +err_out:
> +       kfree(callee);
> +       state->frame[state->curframe + 1] = NULL;
> +       return err;
>  }
>
>  int map_set_for_each_callback_args(struct bpf_verifier_env *env,
> @@ -6969,7 +6974,6 @@ static int prepare_func_exit(struct bpf_verifier_env *env, int *insn_idx)
>                 return -EINVAL;
>         }
>
> -       state->curframe--;
>         caller = state->frame[state->curframe];
>         if (callee->in_callback_fn) {
>                 /* enforce R0 return value range [0, 1]. */
> @@ -7000,6 +7004,7 @@ static int prepare_func_exit(struct bpf_verifier_env *env, int *insn_idx)
>                         return err;
>         }
>
> +       state->curframe--;
>         *insn_idx = callee->callsite + 1;
>         if (env->log.level & BPF_LOG_LEVEL) {
>                 verbose(env, "returning from callee:\n");
> --
> 1.8.3.1
>