From: Xu Kuohai <xukuohai@xxxxxxxxxx> A bpf prog returning positive number attached to file_alloc_security hook will make kernel panic. Here is a panic log: [ 441.235774] BUG: kernel NULL pointer dereference, address: 00000000000009 [ 441.236748] #PF: supervisor write access in kernel mode [ 441.237429] #PF: error_code(0x0002) - not-present page [ 441.238119] PGD 800000000b02f067 P4D 800000000b02f067 PUD b031067 PMD 0 [ 441.238990] Oops: 0002 [#1] PREEMPT SMP PTI [ 441.239546] CPU: 0 PID: 347 Comm: loader Not tainted 6.8.0-rc6-gafe0cbf23373 #22 [ 441.240496] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.15.0-0-g2dd4b4 [ 441.241933] RIP: 0010:alloc_file+0x4b/0x190 [ 441.242485] Code: 8b 04 25 c0 3c 1f 00 48 8b b0 30 0c 00 00 e8 9c fe ff ff 48 3d 00 f0 ff fb [ 441.244820] RSP: 0018:ffffc90000c67c40 EFLAGS: 00010203 [ 441.245484] RAX: ffff888006a891a0 RBX: ffffffff8223bd00 RCX: 0000000035b08000 [ 441.246391] RDX: ffff88800b95f7b0 RSI: 00000000001fc110 RDI: f089cd0b8088ffff [ 441.247294] RBP: ffffc90000c67c58 R08: 0000000000000001 R09: 0000000000000001 [ 441.248209] R10: 0000000000000001 R11: 0000000000000001 R12: 0000000000000001 [ 441.249108] R13: ffffc90000c67c78 R14: ffffffff8223bd00 R15: fffffffffffffff4 [ 441.250007] FS: 00000000005f3300(0000) GS:ffff88803ec00000(0000) knlGS:0000000000000000 [ 441.251053] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 441.251788] CR2: 00000000000001a9 CR3: 000000000bdc4003 CR4: 0000000000170ef0 [ 441.252688] Call Trace: [ 441.253011] <TASK> [ 441.253296] ? __die+0x24/0x70 [ 441.253702] ? page_fault_oops+0x15b/0x480 [ 441.254236] ? fixup_exception+0x26/0x330 [ 441.254750] ? exc_page_fault+0x6d/0x1c0 [ 441.255257] ? asm_exc_page_fault+0x26/0x30 [ 441.255792] ? alloc_file+0x4b/0x190 [ 441.256257] alloc_file_pseudo+0x9f/0xf0 [ 441.256760] __anon_inode_getfile+0x87/0x190 [ 441.257311] ? lock_release+0x14e/0x3f0 [ 441.257808] bpf_link_prime+0xe8/0x1d0 [ 441.258315] bpf_tracing_prog_attach+0x311/0x570 [ 441.258916] ? __pfx_bpf_lsm_file_alloc_security+0x10/0x10 [ 441.259605] __sys_bpf+0x1bb7/0x2dc0 [ 441.260070] __x64_sys_bpf+0x20/0x30 [ 441.260533] do_syscall_64+0x72/0x140 [ 441.261004] entry_SYSCALL_64_after_hwframe+0x6e/0x76 [ 441.261643] RIP: 0033:0x4b0349 [ 441.262045] Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 88 [ 441.264355] RSP: 002b:00007fff74daee38 EFLAGS: 00000246 ORIG_RAX: 0000000000000141 [ 441.265293] RAX: ffffffffffffffda RBX: 00007fff74daef30 RCX: 00000000004b0349 [ 441.266187] RDX: 0000000000000040 RSI: 00007fff74daee50 RDI: 000000000000001c [ 441.267114] RBP: 000000000000001b R08: 00000000005ef820 R09: 0000000000000000 [ 441.268018] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000004 [ 441.268907] R13: 0000000000000004 R14: 00000000005ef018 R15: 00000000004004e8 The reason is that the positive number returned by bpf prog is not a valid errno, and could not be filtered out with IS_ERR which is used by the file system to check errors. As a result, the filesystem mistakenly uses this random positive number as file pointer, causing panic. To fix this issue, there are two schemes: 1. Modify the calling sites of file_alloc_security to take positive return values as zero. 2. Make the bpf verifier to ensure no unpredicted value returned by lsm bpf prog. Considering that hook file_alloc_security never returned positive number before bpf lsm was introduced, and other lsm hooks may have the same problem, scheme 2 is more reasonable. So this series adds lsm return value check in verifier to fix it. v3: 1. Fix incorrect lsm hook return value ranges, and add disabled hook list for bpf lsm, and merge two LSM_RET_INT patches. (KP Singh) 2. Avoid bpf lsm progs attached to different hooks to call each other with tail call 3. Fix a CI failure caused by false rejection of AND operation 4. Add tests v2: https://lore.kernel.org/bpf/20240325095653.1720123-1-xukuohai@xxxxxxxxxxxxxxx/ fix bpf ci failure v1: https://lore.kernel.org/bpf/20240316122359.1073787-1-xukuohai@xxxxxxxxxxxxxxx/ Xu Kuohai (11): bpf, lsm: Annotate lsm hook return value range bpf, lsm: Add helper to read lsm hook return value range bpf, lsm: Check bpf lsm hook return values in verifier bpf, lsm: Add bpf lsm disabled hook list bpf: Avoid progs for different hooks calling each other with tail call bpf: Fix compare error in function retval_range_within bpf: Fix a false rejection caused by AND operation selftests/bpf: Avoid load failure for token_lsm.c selftests/bpf: Add return value checks for failed tests selftests/bpf: Add test for lsm tail call selftests/bpf: Add verifier tests for bpf lsm include/linux/bpf.h | 2 + include/linux/bpf_lsm.h | 8 + include/linux/lsm_hook_defs.h | 591 +++++++++--------- include/linux/lsm_hooks.h | 6 - kernel/bpf/bpf_lsm.c | 84 ++- kernel/bpf/btf.c | 5 +- kernel/bpf/core.c | 22 +- kernel/bpf/verifier.c | 82 ++- security/security.c | 1 + .../selftests/bpf/prog_tests/test_lsm.c | 46 +- .../selftests/bpf/prog_tests/verifier.c | 3 +- tools/testing/selftests/bpf/progs/err.h | 10 + .../selftests/bpf/progs/lsm_tailcall.c | 34 + .../selftests/bpf/progs/test_sig_in_xattr.c | 4 + .../bpf/progs/test_verify_pkcs7_sig.c | 8 +- tools/testing/selftests/bpf/progs/token_lsm.c | 4 +- .../bpf/progs/verifier_global_subprogs.c | 7 +- .../selftests/bpf/progs/verifier_lsm.c | 155 +++++ 18 files changed, 754 insertions(+), 318 deletions(-) create mode 100644 tools/testing/selftests/bpf/progs/lsm_tailcall.c create mode 100644 tools/testing/selftests/bpf/progs/verifier_lsm.c -- 2.30.2
