From: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> 3.12-stable review patch. If anyone has any objections, please let me know. =============== 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@xxxxxxxxxxxx> Signed-off-by: Jiri Slaby <jslaby@xxxxxxx> --- fs/namespace.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/fs/namespace.c b/fs/namespace.c index 6b42c6d1590e..7c3c0f6d2744 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -1347,6 +1347,9 @@ SYSCALL_DEFINE2(umount, char __user *, name, int, flags) goto dput_and_out; if (mnt->mnt.mnt_flags & MNT_LOCKED) goto dput_and_out; + retval = -EPERM; + if (flags & MNT_FORCE && !capable(CAP_SYS_ADMIN)) + goto dput_and_out; retval = do_umount(mnt, flags); dput_and_out: -- 2.2.1 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html