Date: Tue, 12 Aug 2014 16:54:14 -0700 From: Andy Lutomirski <luto@...capital.net> To: oss-security@...ts.openwall.com Subject: Re: CVE Request: ro bind mount bypass using user namespaces On 08/12/2014 02:48 PM, Kenton Varda wrote: > Due to a bug in the Linux kernel's implementation of remount, on systems > with unprivileged user namespaces enabled, it is possible for an > unprivileged user to gain write access to any visible read-only bind mount. > It is also possible to bypass flags like nodev, nosuid, and noexec. > > This problem affects sandboxing / containerization systems that do not > expose the regular filesystem to the sandboxed process, but do expose a > bind-mounted view of that filesystem using these flags to enforce security. > This bug may enable a sandbox break-out. Sandboxes which have used > seccomp-bpf to disable the "mount" system call or to disable user > namespaces are likely safe. nosuid/nodev failures are probably exploitable for full root in many common configurations. --Andy
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