On Fri, Oct 8, 2021 at 9:09 PM Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx> 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@xxxxxxxxxx>
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
> ---
> 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.
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