umount: Disallow unprivileged mount force
commit b2f5d4dc38e034eecb7987e513255265ff9aa1cf upstream. Forced unmount affects not just the mount namespace but the underlying superblock as well. Restrict forced unmount to the global root user for now. Otherwise it becomes possible a user in a less privileged mount namespace to force the shutdown of a superblock of a filesystem in a more privileged mount namespace, allowing a DOS attack on root. Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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@ -1342,6 +1342,9 @@ SYSCALL_DEFINE2(umount, char __user *, name, int, flags)
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goto dput_and_out;
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if (!check_mnt(mnt))
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goto dput_and_out;
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retval = -EPERM;
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if (flags & MNT_FORCE && !capable(CAP_SYS_ADMIN))
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goto dput_and_out;
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retval = do_umount(mnt, flags);
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dput_and_out:
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