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

Eric W. Biederman
2012-04-26T05:29:05Z

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

> 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.

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