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

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Date:	Thu, 26 Apr 2012 00:11:01 +0000
From:	"Serge E. Hallyn" <serge@...lyn.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	"Serge E. Hallyn" <serge@...lyn.com>, linux-kernel@...r.kernel.org,
	Linux Containers <containers@...ts.linux-foundation.org>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	linux-security-module@...r.kernel.org,
	Al Viro <viro@...IV.linux.org.uk>,
	linux-fsdevel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 27/43] userns: Use uid_eq gid_eq helpers when comparing
 kuids and kgids in the vfs

Quoting Eric W. Biederman (ebiederm@...ssion.com):
> "Serge E. Hallyn" <serge@...lyn.com> writes:
> 
> > Quoting Eric W. Beiderman (ebiederm@...ssion.com):
> >> From: Eric W. Biederman <ebiederm@...ssion.com>
> >> 
> >> Signed-off-by: Eric W. Biederman <ebiederm@...ssion.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
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