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Date: Tue, 6 Aug 2013 18:47:45 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: security@...nel.org, oss-security@...ts.openwall.com,
Petr Matousek <pmatouse@...hat.com>
Cc: "Eric W. Biederman" <ebiederm@...ssion.com>,
Andy Lutomirski <luto@...capital.net>
Subject: Re: CLONE_NEWUSER local DoS
On 08/06, Petr Matousek wrote:
>
> spender reported [1] a local DoS triggerable by unprivileged user when
> user namespaces are enabled (CONFIG_USER_NS).
>
> [1] https://twitter.com/grsecurity/status/364566062336978944
>
> Reproducer:
>
> b836010000bb00000010cd80ebf2 is for(;;)unshare(1<<28);
What happens? OOM?
I'll recheck, but at first glance this is simple, unshare_userns()
populates new_cred which is not freed by bad_unshare_cleanup_fd
if create_user_ns() fails. And create_user_ns() _should_ fail (iiuc)
when CLONE_NEWUSER is called for the second time and later due to
!kuid_has_mapping().
I'll send the patch, but perhaps there is something else. Eric?
Oleg.
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