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    SubjectRe: [PATCH v2 0/9] procfs: protect /proc/<pid>/* files with file->f_cred

    * Djalal Harouni <> wrote:

    > * You can't do it for /proc/*/stat otherwise you will break userspace
    > "ps"..., ps must access /proc/1/stat etc... so the proposed solution
    > will work without any side effect.

    The thing is, returning -EINVAL is not the only way to reject access to
    privileged information!

    In the /proc/1/stat case a compatibility quirk can solve the problem:
    create a special 'dummy' process inode for invalid accesses and give it to
    ps, with all fields present but zero.

    > And for /proc/*/maps you will perhaps break glibc under certain
    > situations... so just hold it for the moment and test it
    > later. There have been reports in the past about it.

    Same deal: just create a dummy compat-quirk maps inode with constant, zero
    information contents to placate old user-space:

    00000000-00000000 ---p 00000000 00:00 0

    [ Or whatever line is needed to minimally not break old userspace. ]

    But don't leak privileged information!

    ( Maybe add a CONFIG_PROC_FS_COMPAT_QUIRKS Kconfig option, default-y for
    now, that new/sane userspace can turn off. )



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