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CVE-2016-2383: security - CVE Request: Linux: Incorrect branch fixups for eBPF allow arbitrary read

The adjust_branches function in kernel/bpf/verifier.c in the Linux kernel before 4.5 does not consider the delta in the backward-jump case, which allows local users to obtain sensitive information from kernel memory by creating a packet filter and then loading crafted BPF instructions.

8 years ago

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Date: Sun, 14 Feb 2016 15:52:17 +0100 From: Salvatore Bonaccorso <carnil@…ian.org> To: OSS Security Mailinglist <oss-security@…ts.openwall.com> Cc: Ben Hutchings <benh@…ian.org> Subject: CVE Request: Linux: Incorrect branch fixups for eBPF allow arbitrary read

We would like to request a CVE for the following issue fixed in Linux with the following commit, which as well contains an analysis:

https://git.kernel.org/linus/a1b14d27ed0965838350f1377ff97c93ee383492 (will be in v4.5-rc4):

When ctx access is used, the kernel often needs to expand/rewrite instructions, so after that patching, branch offsets have to be adjusted for both forward and backward jumps in the new eBPF program, but for backward jumps it fails to account the delta. Meaning, for example, if the expansion happens exactly on the insn that sits at the jump target, it doesn’t fix up the back jump offset.

The issue was introduced in v4.1-rc1 with commit https://git.kernel.org/linus/9bac3d6d548e5cc925570b263f35b70a00a00ffd .

Could you please assign a CVE for this issue?

Regards, Salvatore

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