(Maybe a good first-timer bug if anyone wants to try contributing during the holiday seasons)

The stable v6.6 kernel currently runs into kernel panic when running the test_progs tests from BPF selftests. Judging by the log it is failing in one of the dummy_st_ops tests (which comes after deny_namespace tests if you look at the output of `test_progs -l`). My guess is that it is related to "check bpf_dummy_struct_ops program params for test runs"[1], perhaps we're missing a commit or two.

Some notes for anyone tackling this for the first time: 1. You'll need to use the stable/linux-6.6.y branch from https://github.com/shunghsiyu/bpf. The current v6.6.66 one fails at compiling of BPF selftests[2] 2. The easiest way to run BPF selftests is to got relevant dependencies[3] installed, and run tools/testing/selftests/bpf/vmtest.sh (need to give it `-i` to download the root image first, and also might need to specify clang and llvm-strip by setting environmental variable CLANG=clang-17 and LLVM_STRIP=llvm-strip-17, respectively). For a more solid setup, see materials[4][5] from Manu Bretelle 3. Patch(es) should be send to stable@vger.kernel.org, following the stable process[6], see [2] as an example

Below is the output from vmtest.sh:

#68/1 deny_namespace/unpriv_userns_create_no_bpf:OK #68/2 deny_namespace/userns_create_bpf:OK #68 deny_namespace:OK [ 26.829153] BUG: kernel NULL pointer dereference, address: 0000000000000000 [ 26.831136] #PF: supervisor read access in kernel mode [ 26.832635] #PF: error_code(0x0000) - not-present page [ 26.833999] PGD 0 P4D 0 [ 26.834771] Oops: 0000 [#1] PREEMPT SMP PTI [ 26.835997] CPU: 2 PID: 119 Comm: test_progs Tainted: G OE 6.6.66-00003-gd80551078e71 #3 [ 26.838774] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-2 04/01/2014 [ 26.841152] RIP: 0010:bpf_prog_8ee9cbe7c9b5a50f_test_1+0x17/0x24 [ 26.842877] Code: 00 00 00 cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc f3 0f 1e fa 0f 1f 44 00 00 66 90 55 48 89 e5 f3 0f 1e fa 48 8b 7f 00 <8b> 47 00 be 5a 00 00 00 89 77 00 c9 c3 cc cc cc cc cc cc cc cc c0 [ 26.847953] RSP: 0018:ffff9e6b803b7d88 EFLAGS: 00010202 [ 26.849425] RAX: 0000000000000001 RBX: 0000000000000001 RCX: 2845e103d7dffb60 [ 26.851483] RDX: 0000000000000000 RSI: 0000000084d09025 RDI: 0000000000000000 [ 26.853508] RBP: ffff9e6b803b7d88 R08: 0000000000000001 R09: 0000000000000000 [ 26.855670] R10: 0000000000000000 R11: 0000000000000000 R12: ffff9754c0b5f700 [ 26.857824] R13: ffff9754c09cc800 R14: ffff9754c0b5f680 R15: ffff9754c0b5f760 [ 26.859741] FS: 00007f77dee12740(0000) GS:ffff9754fbc80000(0000) knlGS:0000000000000000 [ 26.862087] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 26.863705] CR2: 0000000000000000 CR3: 00000001020e6003 CR4: 0000000000170ee0 [ 26.865689] Call Trace: [ 26.866407] <TASK> [ 26.866982] ? __die+0x24/0x70 [ 26.867774] ? page_fault_oops+0x15b/0x450 [ 26.868882] ? search_bpf_extables+0xb0/0x160 [ 26.870076] ? fixup_exception+0x26/0x330 [ 26.871214] ? exc_page_fault+0x64/0x190 [ 26.872293] ? asm_exc_page_fault+0x26/0x30 [ 26.873352] ? bpf_prog_8ee9cbe7c9b5a50f_test_1+0x17/0x24 [ 26.874705] ? __bpf_prog_enter+0x3f/0xc0 [ 26.875718] ? bpf_struct_ops_test_run+0x1b8/0x2c0 [ 26.876942] ? __sys_bpf+0xc4e/0x2c30 [ 26.877898] ? __x64_sys_bpf+0x20/0x30 [ 26.878812] ? do_syscall_64+0x37/0x90 [ 26.879704] ? entry_SYSCALL_64_after_hwframe+0x78/0xe2 [ 26.880918] </TASK> [ 26.881409] Modules linked in: bpf_testmod(OE) [last unloaded: bpf_testmod(OE)] [ 26.883095] CR2: 0000000000000000 [ 26.883934] ---[ end trace 0000000000000000 ]--- [ 26.885099] RIP: 0010:bpf_prog_8ee9cbe7c9b5a50f_test_1+0x17/0x24 [ 26.886452] Code: 00 00 00 cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc f3 0f 1e fa 0f 1f 44 00 00 66 90 55 48 89 e5 f3 0f 1e fa 48 8b 7f 00 <8b> 47 00 be 5a 00 00 00 89 77 00 c9 c3 cc cc cc cc cc cc cc cc c0 [ 26.890379] RSP: 0018:ffff9e6b803b7d88 EFLAGS: 00010202 [ 26.891450] RAX: 0000000000000001 RBX: 0000000000000001 RCX: 2845e103d7dffb60 [ 26.892779] RDX: 0000000000000000 RSI: 0000000084d09025 RDI: 0000000000000000 [ 26.894254] RBP: ffff9e6b803b7d88 R08: 0000000000000001 R09: 0000000000000000 [ 26.895630] R10: 0000000000000000 R11: 0000000000000000 R12: ffff9754c0b5f700 [ 26.897008] R13: ffff9754c09cc800 R14: ffff9754c0b5f680 R15: ffff9754c0b5f760 [ 26.898337] FS: 00007f77dee12740(0000) GS:ffff9754fbc80000(0000) knlGS:0000000000000000 [ 26.899972] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 26.901076] CR2: 0000000000000000 CR3: 00000001020e6003 CR4: 0000000000170ee0 [ 26.902336] Kernel panic - not syncing: Fatal exception [ 26.903639] Kernel Offset: 0x36000000 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff) [ 26.905693] ---[ end Kernel panic - not syncing: Fatal exception ]---

1: https://lore.kernel.org/all/20240424012821.595216-1-eddyz87@gmail.com/t/#u 2: https://lore.kernel.org/all/20241217080240.46699-1-shung-hsi.yu@suse.com/t/#... 3: https://gist.github.com/shunghsiyu/1bd4189654cce5b3e55c2ab8da7dd33d#file-vmt... 4: https://chantra.github.io/bpfcitools/bpf-local-development.html 5: http://oldvger.kernel.org/bpfconf2024_material/BPF-dev-hacks.pdf 6: https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html