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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Message-ID: <m1wr53f46l.fsf@fess.ebiederm.org>
Date:	Wed, 25 Apr 2012 22:33:06 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	"Serge E. Hallyn" <serge@...lyn.com>
Cc:	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

"Serge E. Hallyn" <serge@...lyn.com> writes:

> 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.

Thanks for testing.  Just reading through I was not certain if we had
the change in creds that commit_creds needed to trigger the set_dumpable
logic.

Eric
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