On Mon, Mar 25, 2024 at 10:53 AM Xu Kuohai <xukuohai@xxxxxxxxxxxxxxx> wrote: > > 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 patch set adds lsm return value check in verifier to fix it. > > v2: > fix bpf ci failure > > v1: > https://lore.kernel.org/bpf/20240316122359.1073787-1-xukuohai@xxxxxxxxxxxxxxx/ > > Xu Kuohai (7): > bpf, lsm: Annotate lsm hook return integer with new macro LSM_RET_INT > bpf, lsm: Add return value range description for lsm hook > bpf, lsm: Add function to read lsm hook return value range > bpf, lsm: Check bpf lsm hook return values in verifier > bpf: Fix compare error in function retval_range_within > selftests/bpf: Avoid load failure for token_lsm.c > selftests/bpf: Add return value checks and corrections for failed > progs This series does not apply cleanly on any of the following branches: bpf-next bpf linux linux-next or Paul's lsm branches There are just too many merge conflicts in the lsm_hook_defs.h file. - KP
