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64620e0a1e
Both bpf_ringbuf_submit() and bpf_ringbuf_discard() have ARG_PTR_TO_ALLOC_MEM
in their bpf_func_proto definition as their first argument. They both expect
the result from a prior bpf_ringbuf_reserve() call which has a return type of
RET_PTR_TO_ALLOC_MEM_OR_NULL.
Meaning, after a NULL check in the code, the verifier will promote the register
type in the non-NULL branch to a PTR_TO_MEM and in the NULL branch to a known
zero scalar. Generally, pointer arithmetic on PTR_TO_MEM is allowed, so the
latter could have an offset.
The ARG_PTR_TO_ALLOC_MEM expects a PTR_TO_MEM register type. However, the non-
zero result from bpf_ringbuf_reserve() must be fed into either bpf_ringbuf_submit()
or bpf_ringbuf_discard() but with the original offset given it will then read
out the struct bpf_ringbuf_hdr mapping.
The verifier missed to enforce a zero offset, so that out of bounds access
can be triggered which could be used to escalate privileges if unprivileged
BPF was enabled (disabled by default in kernel).
Fixes: 457f44363a ("bpf: Implement BPF ring buffer and verifier support for it")
Reported-by: <tr3e.wang@gmail.com> (SecCoder Security Lab)
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.