On Sun, 2023-09-03 at 12:55 -0700, syzbot wrote: > Hello, > > syzbot found the following issue on: > > HEAD commit: fa09bc40b21a igb: disable virtualization features on 82580 > git tree: net > console+strace: https://syzkaller.appspot.com/x/log.txt?x=13382fa8680000 > kernel config: https://syzkaller.appspot.com/x/.config?x=634e05b4025da9da > dashboard link: https://syzkaller.appspot.com/bug?extid=291100dcb32190ec02a8 > compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40 > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1529c448680000 > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=15db0248680000 > > Downloadable assets: > disk image: https://storage.googleapis.com/syzbot-assets/7ab461d84992/disk-fa09bc40.raw.xz > vmlinux: https://storage.googleapis.com/syzbot-assets/3ac6d43ab2db/vmlinux-fa09bc40.xz > kernel image: https://storage.googleapis.com/syzbot-assets/778d096a134e/bzImage-fa09bc40.xz > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: syzbot+291100dcb32190ec02a8@xxxxxxxxxxxxxxxxxxxxxxxxx > > general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] PREEMPT SMP KASAN > KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007] > CPU: 1 PID: 5055 Comm: syz-executor625 Not tainted 6.5.0-syzkaller-04012-gfa09bc40b21a #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/26/2023 > RIP: 0010:bpf_prog_offload_verifier_prep+0xaa/0x170 kernel/bpf/offload.c:295 > Code: 00 fc ff df 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 a1 00 00 00 48 b8 00 00 00 00 00 fc ff df 4c 8b 65 10 4c 89 e2 48 c1 ea 03 <80> 3c 02 00 0f 85 93 00 00 00 48 b8 00 00 00 00 00 fc ff df 4d 8b > RSP: 0018:ffffc900039ff7f8 EFLAGS: 00010246 > RAX: dffffc0000000000 RBX: ffffc9000156e000 RCX: 0000000000000000 > RDX: 0000000000000000 RSI: ffffffff81a8cf76 RDI: ffff888021b25f10 > RBP: ffff888021b25f00 R08: 0000000000000001 R09: fffffbfff195203d > R10: ffffffff8ca901ef R11: 0000000000000000 R12: 0000000000000000 > R13: 0000000000000005 R14: 0000000000000003 R15: ffffc9000156e060 > FS: 0000555556071380(0000) GS:ffff8880b9900000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 0000000020000100 CR3: 0000000022f6b000 CR4: 00000000003506e0 > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > Call Trace: > <TASK> > bpf_check+0x52f3/0xabd0 kernel/bpf/verifier.c:19762 > bpf_prog_load+0x153a/0x2270 kernel/bpf/syscall.c:2708 > __sys_bpf+0xbb6/0x4e90 kernel/bpf/syscall.c:5335 > __do_sys_bpf kernel/bpf/syscall.c:5439 [inline] > __se_sys_bpf kernel/bpf/syscall.c:5437 [inline] > __x64_sys_bpf+0x78/0xc0 kernel/bpf/syscall.c:5437 > do_syscall_x64 arch/x86/entry/common.c:50 [inline] > do_syscall_64+0x38/0xb0 arch/x86/entry/common.c:80 > entry_SYSCALL_64_after_hwframe+0x63/0xcd > RIP: 0033:0x7f7c0df78ea9 > Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 d1 19 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48 > RSP: 002b:00007ffde3592128 EFLAGS: 00000246 ORIG_RAX: 0000000000000141 > RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f7c0df78ea9 > RDX: 0000000000000090 RSI: 0000000020000940 RDI: 0000000000000005 > RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000100000000 > R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 > R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000 > </TASK> > Modules linked in: > ---[ end trace 0000000000000000 ]--- > RIP: 0010:bpf_prog_offload_verifier_prep+0xaa/0x170 kernel/bpf/offload.c:295 > Code: 00 fc ff df 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 a1 00 00 00 48 b8 00 00 00 00 00 fc ff df 4c 8b 65 10 4c 89 e2 48 c1 ea 03 <80> 3c 02 00 0f 85 93 00 00 00 48 b8 00 00 00 00 00 fc ff df 4d 8b > RSP: 0018:ffffc900039ff7f8 EFLAGS: 00010246 > RAX: dffffc0000000000 RBX: ffffc9000156e000 RCX: 0000000000000000 > RDX: 0000000000000000 RSI: ffffffff81a8cf76 RDI: ffff888021b25f10 > RBP: ffff888021b25f00 R08: 0000000000000001 R09: fffffbfff195203d > R10: ffffffff8ca901ef R11: 0000000000000000 R12: 0000000000000000 > R13: 0000000000000005 R14: 0000000000000003 R15: ffffc9000156e060 > FS: 0000555556071380(0000) GS:ffff8880b9900000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 0000000020000100 CR3: 0000000022f6b000 CR4: 00000000003506e0 > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > ---------------- > Code disassembly (best guess), 3 bytes skipped: > 0: df 48 89 fisttps -0x77(%rax) > 3: fa cli > 4: 48 c1 ea 03 shr $0x3,%rdx > 8: 80 3c 02 00 cmpb $0x0,(%rdx,%rax,1) > c: 0f 85 a1 00 00 00 jne 0xb3 > 12: 48 b8 00 00 00 00 00 movabs $0xdffffc0000000000,%rax > 19: fc ff df > 1c: 4c 8b 65 10 mov 0x10(%rbp),%r12 > 20: 4c 89 e2 mov %r12,%rdx > 23: 48 c1 ea 03 shr $0x3,%rdx > * 27: 80 3c 02 00 cmpb $0x0,(%rdx,%rax,1) <-- trapping instruction > 2b: 0f 85 93 00 00 00 jne 0xc4 > 31: 48 b8 00 00 00 00 00 movabs $0xdffffc0000000000,%rax > 38: fc ff df > 3b: 4d rex.WRB > 3c: 8b .byte 0x8b > > > --- > This report is generated by a bot. It may contain errors. > See https://goo.gl/tpsmEJ for more information about syzbot. > syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxx. > > syzbot will keep track of this issue. See: > https://goo.gl/tpsmEJ#status for how to communicate with syzbot. > > If the bug is already fixed, let syzbot know by replying with: > #syz fix: exact-commit-title > > If you want syzbot to run the reproducer, reply with: > #syz test: git://repo/address.git branch-or-commit-hash > If you attach or paste a git patch, syzbot will apply it before testing. > > If you want to overwrite bug's subsystems, reply with: > #syz set subsystems: new-subsystem > (See the list of subsystem names on the web dashboard) > > If the bug is a duplicate of another bug, reply with: > #syz dup: exact-subject-of-another-report > > If you want to undo deduplication, reply with: > #syz undup > I have an explanation of why this error occurs, but I need an advice on how to fix it. Then NULL pointer deference occurs in the following function from offload.c: int bpf_prog_offload_verifier_prep(struct bpf_prog *prog) { struct bpf_prog_offload *offload; int ret = -ENODEV; down_read(&bpf_devs_lock); offload = prog->aux->offload; if (offload) { ret = offload->offdev->ops->prepare(prog); ^^^^^^ this pointer is NULL offload->dev_state = !ret; } up_read(&bpf_devs_lock); return ret; } # Short explanation (a) call chain bpf_prog_load -> bpf_prog_dev_bound_init -> __bpf_prog_dev_bound_init -> __bpf_offload_dev_netdev_register might insert an instance of struct bpf_offload_netdev with {.offdev == NULL} into hash table offload.c:offdevs; (b) call chain bpf_prog_load -> bpf_check -> bpf_prog_offload_verifier_prep assumes that from (prog->aux->offload != NULL) follows (prog->aux->offload->offdev != NULL) which is not the case because of (a). # Long explanation The reproducer generated by testbot has the following structure: - in a loop call function execute_one(), which does the following system calls in sequence: - socket(AF_INET6, SOCK_RAW, IPPROTO_IGMP) = <some fd> - ioctl(3, SIOCGIFINDEX, {ifr_name="batadv_slave_1"}) = 0 - bpf(BPF_PROG_LOAD, {prog_type=BPF_PROG_TYPE_XDP, ... prog_flags=0x40, prog_ifindex=29, ...}) = -1 EINVAL (referred to as program #1 below) - socket(AF_INET6, SOCK_RAW, IPPROTO_IGMP) = <some fd> - ioctl(4, SIOCGIFINDEX, {ifr_name="batadv_slave_1"}) = 0 - bpf(BPF_PROG_LOAD, {prog_type=BPF_PROG_TYPE_XDP, ... prog_flags=0, ... prog_ifindex=29}) = -1 EINVAL (referred to as program #2 below) The error occurs when second bpf call is processed. Interestingly, if sleep(1) is inserted somewhere between first and second bpf calls error does not occur: @@ -1246,6 +1246,7 @@ void execute_one(void) *(uint32_t*)0x200009cc = 4; syscall(__NR_bpf, /*cmd=*/5ul, /*arg=*/0x20000940ul, /*size=*/0x90ul); res = syscall(__NR_socket, /*domain=*/0xaul, /*type=*/3ul, /*proto=*/2); + // sleep(1); /* uncomment to hide the error */ if (res != -1) r[2] = res; memcpy((void*)0x20000100, "batadv_slave_1\000\000", 16); ## Control flow when error occurs For program #1: - bpf_prog_load(): - bpf_prog_is_dev_bound(prog->aux) is true - bpf_prog_dev_bound_init - prog->aux->offload_requested is 0 (because of 0x40 prog_flags) - __bpf_prog_dev_bound_init - netdev is "batadv_slave_1" - bpf_offload_find_netdev(offload->netdev) == NULL, (this is a lookup in hash table offload.c:offdevs) which triggers a call to __bpf_offload_dev_netdev_register - __bpf_offload_dev_netdev_register(NULL, offload->netdev) registers struct bpf_offload_netdev with {.offdev = NULL} for netdev "batadv_slave_1" in offload.c:offdevs hash table. For program #2: - bpf_prog_load(): - bpf_prog_is_dev_bound(prog->aux) is true - bpf_prog_dev_bound_init - prog->aux->offload_requested is 1 (because of 0x0 prog_flags) - __bpf_prog_dev_bound_init - netdev is "batadv_slave_1" - bpf_offload_find_netdev(offload->netdev) != NULL, this is struct bpf_offload_netdev with {.offdev = NULL} created for program #1 - prog->aux->offload = struct bpf_prog_offload {.offload -> {.offdev = NULL}}, The bpf_prog_offload remembered for prog points to bpf_offload_netdev with .offdev == NULL. - ... - bpf_check - bpf_prog_offload_verifier_prep - prog->aux->offload != NULL, but prog->aux->offload->offdev == NULL => null pointer deference. ## Control flow when error does not occur For program #1: - ... all as in the previous case ... Some worker thread: - kernel/bpf/core.c:bpf_prog_free_deferred, registered for program #1: - bpf_prog_is_dev_bound(aux) is true - bpf_prog_dev_bound_destroy - netdev is "batadv_slave_1" - (!ondev->offdev && list_empty(&ondev->progs)) is true - __bpf_offload_dev_netdev_unregister this removes struct bpf_offload_netdev with {.offdev = NULL} from offload.c:offdevs hash table. For program #2: - bpf_prog_load(): - bpf_prog_is_dev_bound(prog->aux) is true - bpf_prog_dev_bound_init - prog->aux->offload_requested is 1 (because of 0x0 prog_flags) - __bpf_prog_dev_bound_init - netdev is "batadv_slave_1" - bpf_offload_find_netdev(offload->netdev) == NULL - bpf_prog_is_offloaded(prog->aux) is true - -EINVAL is returned.
