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Add a new variant of bpf_d_path() named bpf_path_d_path() which takes the form of a BPF kfunc and enforces KF_TRUSTED_ARGS semantics onto its arguments. This new d_path() based BPF kfunc variant is intended to address the legacy bpf_d_path() BPF helper's susceptability to memory corruption issues [0, 1, 2] by ensuring to only operate on supplied arguments which are deemed trusted by the BPF verifier. Typically, this means that only pointers to a struct path which have been referenced counted may be supplied. In addition to the new bpf_path_d_path() BPF kfunc, we also add a KF_ACQUIRE based BPF kfunc bpf_get_task_exe_file() and KF_RELEASE counterpart BPF kfunc bpf_put_file(). This is so that the new bpf_path_d_path() BPF kfunc can be used more flexibily from within the context of a BPF LSM program. It's rather common to ascertain the backing executable file for the calling process by performing the following walk current->mm->exe_file while instrumenting a given operation from the context of the BPF LSM program. However, walking current->mm->exe_file directly is never deemed to be OK, and doing so from both inside and outside of BPF LSM program context should be considered as a bug. Using bpf_get_task_exe_file() and in turn bpf_put_file() will allow BPF LSM programs to reliably get and put references to current->mm->exe_file. As of now, all the newly introduced BPF kfuncs within this patch are limited to BPF LSM program types. These can be either sleepable or non-sleepable variants of BPF LSM program types. [0] https://lore.kernel.org/bpf/CAG48ez0ppjcT=QxU-jtCUfb5xQb3mLr=5FcwddF_VKfEBPs_Dg@mail.gmail.com/ [1] https://lore.kernel.org/bpf/20230606181714.532998-1-jolsa@kernel.org/ [2] https://lore.kernel.org/bpf/20220219113744.1852259-1-memxor@gmail.com/ Acked-by: Christian Brauner <brauner@kernel.org> Signed-off-by: Matt Bobrowski <mattbobrowski@google.com> Acked-by: Song Liu <song@kernel.org> Link: https://lore.kernel.org/r/20240731110833.1834742-2-mattbobrowski@google.com Signed-off-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 reStructuredText 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.