On Thu, Nov 30, 2023 at 10:52:15AM -0800, Andrii Nakryiko wrote: > Add new kind of BPF kernel object, BPF token. BPF token is meant to > allow delegating privileged BPF functionality, like loading a BPF > program or creating a BPF map, from privileged process to a *trusted* > unprivileged process, all while having a good amount of control over which > privileged operations could be performed using provided BPF token. > > This is achieved through mounting BPF FS instance with extra delegation > mount options, which determine what operations are delegatable, and also > constraining it to the owning user namespace (as mentioned in the > previous patch). > > BPF token itself is just a derivative from BPF FS and can be created > through a new bpf() syscall command, BPF_TOKEN_CREATE, which accepts BPF > FS FD, which can be attained through open() API by opening BPF FS mount > point. Currently, BPF token "inherits" delegated command, map types, > prog type, and attach type bit sets from BPF FS as is. In the future, > having an BPF token as a separate object with its own FD, we can allow > to further restrict BPF token's allowable set of things either at the > creation time or after the fact, allowing the process to guard itself > further from unintentionally trying to load undesired kind of BPF > programs. But for now we keep things simple and just copy bit sets as is. > > When BPF token is created from BPF FS mount, we take reference to the > BPF super block's owning user namespace, and then use that namespace for > checking all the {CAP_BPF, CAP_PERFMON, CAP_NET_ADMIN, CAP_SYS_ADMIN} > capabilities that are normally only checked against init userns (using > capable()), but now we check them using ns_capable() instead (if BPF > token is provided). See bpf_token_capable() for details. > > Such setup means that BPF token in itself is not sufficient to grant BPF > functionality. User namespaced process has to *also* have necessary > combination of capabilities inside that user namespace. So while > previously CAP_BPF was useless when granted within user namespace, now > it gains a meaning and allows container managers and sys admins to have > a flexible control over which processes can and need to use BPF > functionality within the user namespace (i.e., container in practice). > And BPF FS delegation mount options and derived BPF tokens serve as > a per-container "flag" to grant overall ability to use bpf() (plus further > restrict on which parts of bpf() syscalls are treated as namespaced). > > Note also, BPF_TOKEN_CREATE command itself requires ns_capable(CAP_BPF) > within the BPF FS owning user namespace, rounding up the ns_capable() > story of BPF token. > > Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx> > --- Same concerns as in the other mail. For the bpf_token_create() code, Acked-by: Christian Brauner <brauner@xxxxxxxxxx>