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
