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With unprivileged BPF disabled, all cmds associated with the BPF syscall are blocked to users without CAP_BPF/CAP_SYS_ADMIN. However there are use cases where we may wish to allow interactions with BPF programs without being able to load and attach them. So for example, a process with required capabilities loads/attaches a BPF program, and a process with less capabilities interacts with it; retrieving perf/ring buffer events, modifying map-specified config etc. With all BPF syscall commands blocked as a result of unprivileged BPF being disabled, this mode of interaction becomes impossible for processes without CAP_BPF. As Alexei notes "The bpf ACL model is the same as traditional file's ACL. The creds and ACLs are checked at open(). Then during file's write/read additional checks might be performed. BPF has such functionality already. Different map_creates have capability checks while map_lookup has: map_get_sys_perms(map, f) & FMODE_CAN_READ. In other words it's enough to gate FD-receiving parts of bpf with unprivileged_bpf_disabled sysctl. The rest is handled by availability of FD and access to files in bpffs." So key fd creation syscall commands BPF_PROG_LOAD and BPF_MAP_CREATE are blocked with unprivileged BPF disabled and no CAP_BPF. And as Alexei notes, map creation with unprivileged BPF disabled off blocks creation of maps aside from array, hash and ringbuf maps. Programs responsible for loading and attaching the BPF program can still control access to its pinned representation by restricting permissions on the pin path, as with normal files. Signed-off-by: Alan Maguire <alan.maguire@oracle.com> Acked-by: Yonghong Song <yhs@fb.com> Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com> Acked-by: KP Singh <kpsingh@kernel.org> Link: https://lore.kernel.org/r/1652970334-30510-2-git-send-email-alan.maguire@oracle.com Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.