On Fri, Dec 14, 2012 at 2:03 PM, Eric W. Biederman
<ebiederm@xxxxxxxxxxxx> wrote:
>
> Andy Lutomirski <luto@xxxxxxxxxxxxxx> found a nasty little bug in
> the permissions of setns. With unprivileged user namespaces it
> became possible to create new namespaces without privilege.
>
> However the setns calls were relaxed to only require CAP_SYS_ADMIN in
> the user nameapce of the targed namespace.
>
> Which made the following nasty sequence possible.
>
> pid = clone(CLONE_NEWUSER | CLONE_NEWNS);
> if (pid == 0) { /* child */
> system("mount --bind /home/me/passwd /etc/passwd");
> }
> else if (pid != 0) { /* parent */
> char path[PATH_MAX];
> snprintf(path, sizeof(path), "/proc/%u/ns/mnt");
> fd = open(path, O_RDONLY);
> setns(fd, 0);
> system("su -");
> }
>
> Prevent this possibility by requiring CAP_SYS_ADMIN
> in the current user namespace when joing all but the user namespace.
>
> Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
> ---
> fs/namespace.c | 3 ++-
> ipc/namespace.c | 3 ++-
> kernel/pid_namespace.c | 3 ++-
> kernel/utsname.c | 3 ++-
> net/core/net_namespace.c | 3 ++-
> 5 files changed, 10 insertions(+), 5 deletions(-)
Acked-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
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