Commit 6f74ad47 authored by Colin Walters's avatar Colin Walters

core: Update comments around PR_SET_NO_NEW_PRIVS and nosuid mount

We now rely on PR_SET_NO_NEW_PRIVS, so make that clearer.  The old
comment around uid 0 for `SECBIT_NOROOT` was actually wrong, because
we always setuid back to the calling user.
parent 1209d5e8
......@@ -356,13 +356,6 @@ main (int argc,
* privileges, even attempting to execute setuid binaries.
* Following the belt-and-suspenders model, we also make a
* MS_NOSUID bind mount below. I don't think this is strictly
* necessary, but at least we doubly ensure we're not going to
* be executing any setuid binaries from the host's /. It
* doesn't help if there are any other mount points with setuid
* binaries, but `PR_SET_NO_NEW_PRIVS` fixes that.
if (prctl (PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) < 0)
fatal_errno ("prctl (PR_SET_NO_NEW_PRIVS)");
......@@ -375,9 +368,13 @@ main (int argc,
if (mount (NULL, "/", "none", MS_PRIVATE | MS_REC, NULL) < 0)
fatal_errno ("mount(/, MS_PRIVATE | MS_REC)");
/* I had thought that SECBIT_NOROOT was enough to be safe, but Serge E. Hallyn
* pointed out that setuid binaries still change uid to 0. So let's just
* disallow them at the rootfs level.
/* We're going to be creating child mounts, so remount the rootfs here
* as private. In the future we could switch this to MS_SLAVE, but
* I suspect most users won't want host mount points showing up by default.
* We also remount with NOSUID, even though PR_SET_NO_NEW_PRIVS
* should take care of that, following the belt-and-suspenders
* model.
if (mount (NULL, "/", "none", MS_PRIVATE | MS_REMOUNT | MS_NOSUID, NULL) < 0)
fatal_errno ("mount(/, MS_PRIVATE | MS_REC | MS_NOSUID)");
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