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Date: Wed, 6 Sep 2023 15:54:13 +0200
From: Daniel Borkmann <daniel@...earbox.net>
To: Eduard Zingerman <eddyz87@...il.com>,
syzbot <syzbot+291100dcb32190ec02a8@...kaller.appspotmail.com>,
andrii@...nel.org, ast@...nel.org, bpf@...r.kernel.org,
davem@...emloft.net, haoluo@...gle.com, hawk@...nel.org,
john.fastabend@...il.com, jolsa@...nel.org, kpsingh@...nel.org,
kuba@...nel.org, linux-kernel@...r.kernel.org,
martin.lau@...ux.dev, netdev@...r.kernel.org, sdf@...gle.com,
song@...nel.org, syzkaller-bugs@...glegroups.com,
yonghong.song@...ux.dev, horms@...nel.org
Subject: Re: [syzbot] [bpf?] general protection fault in
bpf_prog_offload_verifier_prep
[ 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@...kaller.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@...glegroups.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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