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

* Djalal Harouni <tixxdz@opendz.org> 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. )

Thanks,

Ingo


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