>Vincent Li <vincent.mc.li@xxxxxxxxx> writes: > On Mon, Aug 15, 2022 at 5:05 PM Quentin Monnet <quentin@xxxxxxxxxxxxx> wrote: >> >> On Mon, 15 Aug 2022 at 23:26, Vincent Li <vincent.mc.li@xxxxxxxxx> wrote: >> > >> > On Mon, Aug 15, 2022 at 3:18 PM Quentin Monnet <quentin@xxxxxxxxxxxxx> wrote: >> > > >> > > Hi Vincent, >> > > >> > > On Mon, 15 Aug 2022 at 18:46, Vincent Li <vincent.mc.li@xxxxxxxxx> wrote: >> > > > >> > > > Hi, >> > > > >> > > > I compile and run kernel 5.18.0 in Centos 8 from bpf-next in my dev >> > > > machine, I also compiled bpftool from bpf-next on same machine, when >> > > > run bpftool on same machine, I got : >> > > > >> > > > ./bpftool feature probe >> > > > >> > > > Error: bug: failed to retrieve CAP_BPF status: Invalid argument >> > > > >> > > > where bpftool to retrieve CAP_BPF ? from running kernel or from somewhere else? >> > > >> > > Yes, bpftool calls cap_get_proc() to get the capabilities of the >> > > current process. From what I understand of your output, it looks like >> > > capget() returns CAP_BPF: I believe the "0x1c0" value at the end is >> > > (1<<(CAP_CHECKPOINT_RESTORE-32)) + (1<<(CAP_BPF-32)) + >> > > (1<<(CAP_PERFMON-32)). You could probably check this with a more >> > > recent version of strace. >> > > >> > > Then assuming you do retrieve CAP_BPF from capget(), I don't know why >> > > cap_get_flag() in bpftool fails to retrieve the capability state. It >> > > would be worth running bpftool in GDB to check what happens. The check >> > > in libcap is here [0] but I don't see where we would fail to provide >> > > valid arguments. Just in case, could you please let me know what >> > > version of libcap you're using when compiling bpftool? >> > >> > I think I installed libcap through centos distro >> > >> > [root@centos-dev ~]# rpm -qi libcap.x86_64 >> > >> > Name : libcap >> > >> > Version : 2.26 >> >> So we investigated this on Slack. The issue is related to libcap (and >> to how libcap is built on CentOS); it is fixed in libcap 2.30 and >> older. >> >> For the record, this is the commit that fixed it: >> https://git.kernel.org/pub/scm/libs/libcap/libcap.git/commit/?id=f1f62a748d7c67361e91e32d26abafbfb03eeee4 >> >> Before this, cap_get_flag() would compare its argument "value" (in our >> case, CAP_BPF == 39) with __CAP_BITS. This __CAP_BITS constant is >> defined in libcap/cap_names.h, generated by libcap/_makenames.c from >> the list in libcap/cap_names.list.h. The latter header file is itself >> generated in libcap/Makefile from the UAPI header at >> $(KERNEL_HEADERS)/linux/capability.h, which defaults to the local >> libcap/include/uapi/linux/capability.h. >> >> On your CentOS, the libcap version may have been compiled without >> setting KERNEL_HEADERS to make it point to the correct system UAPI >> header (or the header could be too old, but looking at it, it seems >> that it does have CAP_BPF), in which case it defaulted to libcap's >> version of the header, which in 2.26 stops at CAP_AUDIT (37). In that >> case, __CAP_BITS is worth 37 and is lower than CAP_BPF, the check in >> cap_get_flag() fails and we get -EINVAL. >> >> The commit referenced above changed the comparison for libcap 2.30+ to >> compare "value" with __CAP_MAXBITS == 64 instead, which works >> correctly. >> >> Thanks for the report and the shared debug session! >> Quentin > > Thanks Quentin for your quick response and analysis :) FYI, CAP_BPF should also be fixed in the version of libcap shipped with RHEL8.5 (version libcap-2.26-5.el8). This should be available in CentOS Stream as well, so just updating the package should be enough... -Toke
