On Mon, Apr 4, 2022 at 10:21 AM Roberto Sassu <roberto.sassu@xxxxxxxxxx> wrote: > > > From: Djalal Harouni [mailto:tixxdz@xxxxxxxxx] > > Sent: Monday, April 4, 2022 9:45 AM > > On Sun, Apr 3, 2022 at 5:42 PM KP Singh <kpsingh@xxxxxxxxxx> wrote: > > > > > > On Sat, Apr 2, 2022 at 1:55 AM Alexei Starovoitov > > > <alexei.starovoitov@xxxxxxxxx> wrote: > > ... > > > > > > > > > Pinning > > > > > them to unreachable inodes intuitively looked the > > > > > way to go for achieving the stated goal. > > > > > > > > We can consider inodes in bpffs that are not unlinkable by root > > > > in the future, but certainly not for this use case. > > > > > > Can this not be already done by adding a BPF_LSM program to the > > > inode_unlink LSM hook? > > > > > > > Also, beside of the inode_unlink... and out of curiosity: making sysfs/bpffs/ > > readonly after pinning, then using bpf LSM hooks > > sb_mount|remount|unmount... > > family combining bpf() LSM hook... isn't this enough to: > > 1. Restrict who can pin to bpffs without using a full MAC > > 2. Restrict who can delete or unmount bpf filesystem > > > > ? > > I'm thinking to implement something like this. > > First, I add a new program flag called > BPF_F_STOP_ONCONFIRM, which causes the ref count > of the link to increase twice at creation time. In this way, > user space cannot make the link disappear, unless a > confirmation is explicitly sent via the bpf() system call. > > Another advantage is that other LSMs can decide > whether or not they allow a program with this flag > (in the bpf security hook). > > This would work regardless of the method used to > load the eBPF program (user space or kernel space). > > Second, I extend the bpf() system call with a new > subcommand, BPF_LINK_CONFIRM_STOP, which > decreases the ref count for the link of the programs > with the BPF_F_STOP_ONCONFIRM flag. I will also > introduce a new security hook (something like > security_link_confirm_stop), so that an LSM has the > opportunity to deny the stop (the bpf security hook > would not be sufficient to determine exactly for > which link the confirmation is given, an LSM should > be able to deny the stop for its own programs). > > What do you think? Hack upon a hack? Makes no sense.
