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SubjectRe: [Linux-kernel-mentees] [PATCH v3] bpf: Fix NULL pointer dereference in __btf_resolve_helper_id()
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On 7/14/20 8:09 PM, Peilin Ye wrote:
> Prevent __btf_resolve_helper_id() from dereferencing `btf_vmlinux`
> as NULL. This patch fixes the following syzbot bug:
>
> https://syzkaller.appspot.com/bug?id=f823224ada908fa5c207902a5a62065e53ca0fcc
>
> Reported-by: syzbot+ee09bda7017345f1fbe6@syzkaller.appspotmail.com
> Signed-off-by: Peilin Ye <yepeilin.cs@gmail.com>

Looks good, applied, thanks! As far as I can tell all the other occurrences are
gated behind btf_parse_vmlinux() where we also init struct_opts, etc.

So for bpf-next this would then end up looking like ...

int btf_resolve_helper_id(struct bpf_verifier_log *log,
const struct bpf_func_proto *fn, int arg)
{
int id;

if (fn->arg_type[arg] != ARG_PTR_TO_BTF_ID)
return -EINVAL;
id = fn->btf_id[arg];
if (!id || !btf_vmlinux || id > btf_vmlinux->nr_types)
return -EINVAL;
return id;
}

> ---
> Sorry, I got the link wrong. Thank you for pointing that out.
>
> Change in v3:
> - Fix incorrect syzbot dashboard link.
>
> Change in v2:
> - Split NULL and IS_ERR cases.
>
> kernel/bpf/btf.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index 30721f2c2d10..092116a311f4 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -4088,6 +4088,11 @@ static int __btf_resolve_helper_id(struct bpf_verifier_log *log, void *fn,
> const char *tname, *sym;
> u32 btf_id, i;
>
> + if (!btf_vmlinux) {
> + bpf_log(log, "btf_vmlinux doesn't exist\n");
> + return -EINVAL;
> + }
> +
> if (IS_ERR(btf_vmlinux)) {
> bpf_log(log, "btf_vmlinux is malformed\n");
> return -EINVAL;
>

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