Re: [PATCH v3 bpf-next 1/3] bpf: introduce new VFS based BPF kfuncs

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On Fri, Jul 26, 2024 at 1:56 AM Matt Bobrowski <mattbobrowski@xxxxxxxxxx> wrote:
>
> 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 susceptibility 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 flexibility 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 sleepable BPF LSM program types. Therefore, they may only
> be called when a BPF LSM program is attached to one of the listed
> attachment points defined within the sleepable_lsm_hooks BTF ID set.
>
> [0] https://lore.kernel.org/bpf/CAG48ez0ppjcT=QxU-jtCUfb5xQb3mLr=5FcwddF_VKfEBPs_Dg@xxxxxxxxxxxxxx/
> [1] https://lore.kernel.org/bpf/20230606181714.532998-1-jolsa@xxxxxxxxxx/
> [2] https://lore.kernel.org/bpf/20220219113744.1852259-1-memxor@xxxxxxxxx/
>
> Signed-off-by: Matt Bobrowski <mattbobrowski@xxxxxxxxxx>

checkpatch reported a few syntax issues on this one:

https://netdev.bots.linux.dev/static/nipa/874023/13742510/checkpatch/stdout





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