Re: [syzbot] [bpf?] general protection fault in bpf_prog_offload_verifier_prep
From: Eduard Zingerman
Date: Wed Sep 06 2023 - 09:50:34 EST
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@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.
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.