oss-security - Re: [CVE-2021-3493] Ubuntu Linux kernel overlayfs fs caps privilege escalation

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Message-ID: <YHmk/nNvde4ohgSP@eldamar.lan>
Date: Fri, 16 Apr 2021 16:53:50 +0200
From: Salvatore Bonaccorso <carnil@...ian.org>
To: oss-security@...ts.openwall.com
Subject: Re: [CVE-2021-3493] Ubuntu Linux kernel overlayfs fs
 caps privilege escalation

Hi Steve,

On Thu, Apr 15, 2021 at 02:31:14PM -0700, Steve Beattie wrote:
> Hello,
> 
> An independent security researcher reported via the SSD Secure
> Disclosure program that the overlayfs stacking file system within the
> Linux kernel as used within Ubuntu did not properly validate the
> application of file capabilities against user namespaces.
> 
> This issue is likely Ubuntu specific, as Ubuntu carries a patch to
> enable unprivileged overlayfs mounts. The combination of that patch
> plus allowing unprivileged user namespaces by default in Ubuntu allows
> an unprivileged attacker to gain elevated privileges.
> 
> A commit that addresses the issue was applied in the upstream kernel:
> 
>   7c03e2cda4a5 ("vfs: move cap_convert_nscap() call into vfs_setxattr()") (v5.10)

For completeness, this though was in v5.11-rc1 right?

Regards,
Salvatore

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