Re: [PATCH bpf-next v2 2/3] bpf: Add user memory access kfuncs for linux_binprm

> bpf: Add user memory access kfuncs for linux_binprm
>
> When security_bprm_check runs, the arg and env strings for the exec have
> been copied into bprm->mm. The new address space has not been associated
> yet with a task_struct until exec_mmap(), so existing BPF user memory
> helpers can only read from the calling task's old address space.
>
> This patch adds bpf_copy_from_user_bprm() and
> bpf_copy_from_user_bprm_str() kfuncs. Both use the mm_struct provided by
> struct linux_binprm.

This isn't a bug, but could the opener be reworded to avoid "This patch
adds"? Documentation/process/submitting-patches.rst asks for imperative mood
("Add bpf_copy_from_user_bprm() ...").

> Register these kfuncs on both MMU and NOMMU systems. On NOMMU systems,
> exec arguments are staged in bprm->page[] rather than mapped in bprm->mm,
> so the kfuncs return -EOPNOTSUPP.
>
> bpf_copy_from_user_bprm() has similar semantics as
> bpf_copy_from_user_task(). bpf_copy_from_user_bprm_str() copies one
> NUL-terminated string and returns its size including the NUL terminator.
> It accepts BPF_F_PAD_ZEROS to clear unused destination bytes on success.
>
> This patch registers both kfuncs with KF_SLEEPABLE because accessing the
> remote address space can fault. This allows BPF LSM programs attached to
> security_bprm_check to read arguments beginning at bprm->p and reject an
> exec based on its command-line arguments.

Same for "This patch registers" here -- would "Register both kfuncs with
KF_SLEEPABLE ..." fit better?

> Signed-off-by: Anastasios Papagiannis <[email protected]>


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