Messages in this thread | | | Subject | Re: [syzbot] [bpf?] general protection fault in bpf_prog_offload_verifier_prep | From | Daniel Borkmann <> | Date | Wed, 6 Sep 2023 15:54:13 +0200 |
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[ Also adding Simon to Cc ]
On 9/6/23 3:50 PM, Eduard Zingerman wrote: > On Wed, 2023-09-06 at 15:40 +0300, Eduard Zingerman wrote: >> 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@syzkaller.appspotmail.com >>> >>> 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@googlegroups.com. >>> >>> 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. > > I think the fix should look as follows: > > diff --git a/kernel/bpf/offload.c b/kernel/bpf/offload.c > index 3e4f2ec1af06..302e38bffffa 100644 > --- a/kernel/bpf/offload.c > +++ b/kernel/bpf/offload.c > @@ -199,12 +199,11 @@ static int __bpf_prog_dev_bound_init(struct bpf_prog *prog, struct net_device *n > offload->netdev = netdev; > > ondev = bpf_offload_find_netdev(offload->netdev); > + if (bpf_prog_is_offloaded(prog->aux) && (!ondev || !ondev->offdev)) { > + err = -EINVAL; > + goto err_free; > + } > if (!ondev) { > - if (bpf_prog_is_offloaded(prog->aux)) { > - err = -EINVAL; > - goto err_free; > - } > - > /* When only binding to the device, explicitly > * create an entry in the hashtable. > */ > > With the following reasoning: for offloaded programs offload device > should exist and it should not be a fake device create in !ondev branch. > > Stanislav, could you please take a look? I think this is related to commit: > 2b3486bc2d23 ("bpf: Introduce device-bound XDP programs") > >> 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.
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