Re: [PATCH] bpf: btf: Fix a missing-check bug

From: Martin Lau
Date: Mon Oct 22 2018 - 11:41:05 EST

On Fri, Oct 19, 2018 at 05:29:51PM -0500, Wenwen Wang wrote:
> In btf_parse(), the header of the user-space btf data 'btf_data' is firstly
> parsed and verified through btf_parse_hdr(). In btf_parse_hdr(), the header
> is copied from user-space 'btf_data' to kernel-space 'btf->hdr' and then
> verified. If no error happens during the verification process, the whole
> data of 'btf_data', including the header, is then copied to 'data' in
> btf_parse(). It is obvious that the header is copied twice here. More
> importantly, no check is enforced after the second copy to make sure the
> headers obtained in these two copies are same. Given that 'btf_data'
> resides in the user space, a malicious user can race to modify the header
> between these two copies. By doing so, the user can inject inconsistent
> data, which can cause undefined behavior of the kernel and introduce
> potential security risk.
> To avoid the above issue, this patch rewrites the header after the second
> copy, using 'btf->hdr', which is obtained in the first copy.
Acked-by: Martin KaFai Lau <kafai@xxxxxx>