Re: [PATCH 27/43] userns: Use uid_eq gid_eq helpers when comparing kuids and kgids in the vfs

Serge E. Hallyn
2012-04-26T00:09:46Z

Quoting Eric W. Biederman (ebiederm@xmission.com):
> "Serge E. Hallyn" <serge@hallyn.com> writes:
>
> > Quoting Eric W. Beiderman (ebiederm@xmission.com):
> >> From: Eric W. Biederman <ebiederm@xmission.com>
> >>
> >> Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
> >> ---
> >> fs/attr.c | 8 ++++----
> >> fs/exec.c | 10 +++++-----
> >> fs/fcntl.c | 6 +++---
> >> fs/ioprio.c | 4 ++--
> >> fs/locks.c | 2 +-
> >> fs/namei.c | 8 ++++----
> >> include/linux/quotaops.h | 4 ++--
> >> 7 files changed, 21 insertions(+), 21 deletions(-)
> >>
>
> >> @@ -2120,7 +2120,7 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs)
> >> if (__get_dumpable(cprm.mm_flags) == 2) {
> >> /* Setuid core dump mode */
> >> flag = O_EXCL; /* Stop rewrite attacks */
> >> - cred->fsuid = 0; /* Dump root private */
> >> + cred->fsuid = GLOBAL_ROOT_UID; /* Dump root private */
> >
> > Sorry, one more - can this be the per-ns root uid? The coredumps should
> > be ok to belong to privileged users in the namespace right?
>
> I'm not certain it was clear when you were looking at this that
> this is about dumping core from suid applications, not normal
> applications.
>
> Looking at the code in commoncap and commit_creds it looks like it is a
> bug that we don't call set_dumpable(new, suid_dumpable) in common cap
> when we use file capabilities. I might be wrong but I think we escape

We do, check kernel/cred.c:commit_creds(). So long as the new permitted
set is not a subset of the old one.

Tested it to make absolutely sure. When I add file capabilities to a
program that otherwise dumps core (int *x = 0; *x = 0;), core dumps are
no longer generated.

-serge