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. Cc: stable@xxxxxxxxxxxxxxx Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> --- fs/namespace.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/fs/namespace.c b/fs/namespace.c index 3a1a87dc33df..43b16af8af30 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -1544,6 +1544,9 @@ 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: -- 1.9.1 -- 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