Messages in this thread | | | Subject | Re: [PATCH v2] bpf: btf: Fix a missing-check bug | From | Daniel Borkmann <> | Date | Fri, 26 Oct 2018 00:58:31 +0200 |
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On 10/24/2018 10:42 PM, Martin Lau wrote: > On Wed, Oct 24, 2018 at 06:22:46PM +0000, Martin Lau wrote: >> On Wed, Oct 24, 2018 at 05:26:23PM +0000, Martin Lau wrote: >>> On Wed, Oct 24, 2018 at 08:00:19AM -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. >> btw, I am working on a patch that copies the btf_data before parsing/verifying >> the header. That should avoid this from happening but that will >> require a bit more code churns for the bpf branch. >> > It is what I have in mind: > > It is not a good idea to check the BTF header before copying the > user btf_data. The verified header may not be the one actually > copied to btf->data (e.g. userspace may modify the passed in > btf_data in between). Like the one fixed in > commit 8af03d1ae2e1 ("bpf: btf: Fix a missing check bug"). > > This patch copies the user btf_data before parsing/verifying > the BTF header. > > Fixes: 69b693f0aefa ("bpf: btf: Introduce BPF Type Format (BTF)") > Signed-off-by: Martin KaFai Lau <kafai@fb.com>
I've added Co-developed-by tag and applied it to bpf tree, thanks everyone!
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