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

[Matt Bobrowski <mattbobrowski@google.com>]

On Fri, Jul 26, 2024 at 04:52:50PM -0700, Song Liu wrote:
> On Fri, Jul 26, 2024 at 1:56 AM Matt Bobrowski <mattbobrowski@google.com> 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@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/
> >
> > Signed-off-by: Matt Bobrowski <mattbobrowski@google.com>
> 
> checkpatch reported a few syntax issues on this one:
> 
> https://netdev.bots.linux.dev/static/nipa/874023/13742510/checkpatch/stdout

Thanks for making aware, all has been addressed.

/M