Re: [PATCH bpf] bpf: Fix tr dereferencing

[Jiri Olsa <olsajiri@gmail.com>]

On Thu, Sep 14, 2023 at 10:51:26PM +0800, Leon Hwang wrote:
> Fix 'tr' dereferencing bug when CONFIG_BPF_JIT is turned off.
> 
> Like 'bpf_trampoline_get_progs()', return 'ERR_PTR()' and then check by
> 'IS_ERR()'. As a result, when CONFIG_BPF_JIT is turned off, it's able to
> handle the case that 'bpf_trampoline_get()' returns
> 'ERR_PTR(-EOPNOTSUPP)'.
> 
> Fixes: 4a1e7c0c63e0 ("bpf: Support attaching freplace programs to multiple attach points")
> Fixes: f7b12b6fea00 ("bpf: verifier: refactor check_attach_btf_id()")
> Fixes: 69fd337a975c ("bpf: per-cgroup lsm flavor")
> Reported-by: kernel test robot <lkp@intel.com>
> Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
> Closes: https://lore.kernel.org/r/202309131936.5Nc8eUD0-lkp@intel.com/
> Signed-off-by: Leon Hwang <hffilwlqm@gmail.com>

it does not apply cleanly on bpf/master for me, but nice catch

Acked-by: Jiri Olsa <jolsa@kernel.org>

jirka

> ---
>  kernel/bpf/syscall.c    | 4 ++--
>  kernel/bpf/trampoline.c | 6 +++---
>  kernel/bpf/verifier.c   | 4 ++--
>  3 files changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 6a692f3bea150..5748d01c99854 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -3211,8 +3211,8 @@ static int bpf_tracing_prog_attach(struct bpf_prog *prog,
>  		}
>  
>  		tr = bpf_trampoline_get(key, &tgt_info);
> -		if (!tr) {
> -			err = -ENOMEM;
> +		if (IS_ERR(tr)) {
> +			err = PTR_ERR(tr);
>  			goto out_unlock;
>  		}
>  	} else {
> diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
> index e97aeda3a86b5..1952614778433 100644
> --- a/kernel/bpf/trampoline.c
> +++ b/kernel/bpf/trampoline.c
> @@ -697,8 +697,8 @@ int bpf_trampoline_link_cgroup_shim(struct bpf_prog *prog,
>  
>  	bpf_lsm_find_cgroup_shim(prog, &bpf_func);
>  	tr = bpf_trampoline_get(key, &tgt_info);
> -	if (!tr)
> -		return  -ENOMEM;
> +	if (IS_ERR(tr))
> +		return PTR_ERR(tr);
>  
>  	mutex_lock(&tr->mutex);
>  
> @@ -775,7 +775,7 @@ struct bpf_trampoline *bpf_trampoline_get(u64 key,
>  
>  	tr = bpf_trampoline_lookup(key);
>  	if (!tr)
> -		return NULL;
> +		return ERR_PTR(-ENOMEM);
>  
>  	mutex_lock(&tr->mutex);
>  	if (tr->func.addr)
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 18e673c0ac159..054063ead0e54 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -19771,8 +19771,8 @@ static int check_attach_btf_id(struct bpf_verifier_env *env)
>  
>  	key = bpf_trampoline_compute_key(tgt_prog, prog->aux->attach_btf, btf_id);
>  	tr = bpf_trampoline_get(key, &tgt_info);
> -	if (!tr)
> -		return -ENOMEM;
> +	if (IS_ERR(tr))
> +		return PTR_ERR(tr);
>  
>  	if (tgt_prog && tgt_prog->aux->tail_call_reachable)
>  		tr->flags = BPF_TRAMP_F_TAIL_CALL_CTX;
> 
> base-commit: cbb1dbcd99b0ae74c45c4c83c6d213c12c31785c
> -- 
> 2.41.0
> 
>