From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Cc: bpf <bpf@vger.kernel.org>, Andrii Nakryiko <andrii@kernel.org>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>
Subject: Re: [PATCH bpf-next v3] bpf: Silence Coverity warning for find_kfunc_desc_btf
Date: Wed, 20 Oct 2021 09:57:37 -0700 [thread overview]
Message-ID: <CAEf4BzZe+VW+hRMOZpR3ZyRs_6TuTQRXN4tinwnq8krrVt2gOw@mail.gmail.com> (raw)
In-Reply-To: <20211009040900.803436-1-memxor@gmail.com>
On Fri, Oct 8, 2021 at 9:09 PM Kumar Kartikeya Dwivedi <memxor@gmail.com> wrote:
>
> The helper function returns a pointer that in the failure case encodes
> an error in the struct btf pointer. The current code lead to Coverity
> warning about the use of the invalid pointer:
>
> *** CID 1507963: Memory - illegal accesses (USE_AFTER_FREE)
> /kernel/bpf/verifier.c: 1788 in find_kfunc_desc_btf()
> 1782 return ERR_PTR(-EINVAL);
> 1783 }
> 1784
> 1785 kfunc_btf = __find_kfunc_desc_btf(env, offset, btf_modp);
> 1786 if (IS_ERR_OR_NULL(kfunc_btf)) {
> 1787 verbose(env, "cannot find module BTF for func_id %u\n", func_id);
> >>> CID 1507963: Memory - illegal accesses (USE_AFTER_FREE)
> >>> Using freed pointer "kfunc_btf".
> 1788 return kfunc_btf ?: ERR_PTR(-ENOENT);
> 1789 }
> 1790 return kfunc_btf;
> 1791 }
> 1792 return btf_vmlinux ?: ERR_PTR(-ENOENT);
> 1793 }
>
> Daniel suggested the use of ERR_CAST so that the intended use is clear
> to Coverity, but on closer look it seems that we never return NULL from
> the helper. Andrii noted that since __find_kfunc_desc_btf already logs
> errors for all cases except btf_get_by_fd, it is much easier to add
> logging for that and remove the IS_ERR check altogether, returning
> directly from it.
>
> Suggested-by: Andrii Nakryiko <andrii@kernel.org>
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
> ---
> v2->v3
> * Remove unused variable (Kernel Test Robot)
> v1->v2
> * Remove error check, log btf_get_by_fd failure (Andrii)
> ---
Patch bot missed this one. Applied yesterday to bpf-next. Thanks.
[...]
prev parent reply other threads:[~2021-10-20 16:57 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-08 17:07 [PATCH bpf-next] bpf: Silence Coverity warning for find_kfunc_desc_btf Kumar Kartikeya Dwivedi
2021-10-08 20:39 ` Andrii Nakryiko
2021-10-08 22:27 ` [PATCH bpf-next v2] " Kumar Kartikeya Dwivedi
2021-10-09 4:09 ` [PATCH bpf-next v3] " Kumar Kartikeya Dwivedi
2021-10-20 16:57 ` Andrii Nakryiko [this message]
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