Re: BUG: unable to handle kernel NULL pointer dereference in sk_diag_fill

From: Kuniyuki Iwashima
Date: Mon Nov 21 2022 - 23:37:24 EST

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In reply to: Eric Dumazet: "Re: BUG: unable to handle kernel NULL pointer dereference in sk_diag_fill"
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From: Eric Dumazet <edumazet@xxxxxxxxxx>
Date: Mon, 21 Nov 2022 20:01:20 -0800
> On Mon, Nov 21, 2022 at 3:10 PM Kuniyuki Iwashima <kuniyu@xxxxxxxxxx> wrote:
> >
> > Hi Wei,
> >
> > Thanks for reporting the issue.
> >
> > From: Wei Chen <harperchen1110@xxxxxxxxx>
> > Date: Mon, 21 Nov 2022 21:34:50 +0800
> > > Dear Linux Developer,
> > >
> > > Recently when using our tool to fuzz kernel, the following crash was triggered.
> > >
> > > HEAD commit: 147307c69ba
> > > git tree: upstream
> > > compiler: clang 12.0.0
> > > console output:
> > > https://drive.google.com/file/d/1WZBgd9dodq3qWgqIXNNBHNEpayHthWr5/view?usp=share_link
> > > kernel config: https://drive.google.com/file/d/1NAf4S43d9VOKD52xbrqw-PUP1Mbj8z-S/view?usp=share_link
> > >
> > > Unfortunately, I didn't have a reproducer for this crash. My manual
> > > check identifies that sk->sk_socket in sk_user_ns is null.
> >
> > This gave me a hint.
> >
> > I guess syzbot is dumping an AF_UNIX sk while close()ing it concurrently.
> > Then, there seems to be a minor race like
> >
> > unix_release unix_diag_handler_dump <-- called after refcnt reaches 0
> > unix_release_sock unix_diag_get_exact
> > unix_lookup_by_ino
> > sock_hold
> > unix_remove_socket <-- after this, sk cannot be seen in the hash table
> > unix_remove_bsd_socket
> > sock_orphan
>
> Note that sock_orphan() is called while sk_refcnt is not 0 yet.
> (sock_put() is called at line 655)

Ah, thank you Eric!

Somehow I was thinking unix_release() was called when refcnt
reaches 0, which is called when f_count reaches 0.

Then, we cannot fix it by inc_not_zero()...

>
> > sk->sk_socket = NULL <-- clear the sk->sk_socket
> > sk_diag_fill
> > sk_diag_dump_uid
> > sk_user_ns
> > sk->sk_socket->file->f_cred->user_ns <-- NULL deref
> >
> > It seems we need to call refcnt_inc_not_zero() instead of sock_hold() in
> > unix_lookup_by_ino(), so the fix would be like this.
>
> If this was the case, unix_find_socket_byname() would have a similar issue ?

Yes, but I think it's ok because we always check SOCK_DEAD after
unix_find_other().

So, I guess we have to apply the same rule for netlink ?

>
> >
> > After checking other paths (at least netlink_dump_start() path) and doing
> > some tests, I'll submit a patch.
> >
> > ---8<---
> > diff --git a/net/unix/diag.c b/net/unix/diag.c
> > index 105f522a89fe..581500296515 100644
> > --- a/net/unix/diag.c
> > +++ b/net/unix/diag.c
> > @@ -241,8 +241,8 @@ static struct sock *unix_lookup_by_ino(struct net *net, unsigned int ino)
> > for (i = 0; i < UNIX_HASH_SIZE; i++) {
> > spin_lock(&net->unx.table.locks[i]);
> > sk_for_each(sk, &net->unx.table.buckets[i]) {
> > - if (ino == sock_i_ino(sk)) {
> > - sock_hold(sk);
> > + if (ino == sock_i_ino(sk) &&
> > + refcount_inc_not_zero(&sk->sk_refcnt)) {
> > spin_unlock(&net->unx.table.locks[i]);
> > return sk;
> > }
> > ---8<---
> >
> > Thank you.
> >
> >
> > >
> > > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > > Reported-by: Wei Chen <harperchen1110@xxxxxxxxx>
> > >
> > > BUG: kernel NULL pointer dereference, address: 0000000000000270
> > > #PF: supervisor read access in kernel mode
> > > #PF: error_code(0x0000) - not-present page
> > > PGD 12bbce067 P4D 12bbce067 PUD 12bc40067 PMD 0
> > > Oops: 0000 [#1] PREEMPT SMP
> > > CPU: 0 PID: 27942 Comm: syz-executor.0 Not tainted 6.1.0-rc5-next-20221118 #2
> > > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> > > rel-1.13.0-48-gd9c812dda519-prebuilt.qemu.org 04/01/2014
> > > RIP: 0010:sk_user_ns include/net/sock.h:920 [inline]
> > > RIP: 0010:sk_diag_dump_uid net/unix/diag.c:119 [inline]
> > > RIP: 0010:sk_diag_fill+0x77d/0x890 net/unix/diag.c:170
> > > Code: 89 ef e8 66 d4 2d fd c7 44 24 40 00 00 00 00 49 8d 7c 24 18 e8
> > > 54 d7 2d fd 49 8b 5c 24 18 48 8d bb 70 02 00 00 e8 43 d7 2d fd <48> 8b
> > > 9b 70 02 00 00 48 8d 7b 10 e8 33 d7 2d fd 48 8b 5b 10 48 8d
> > > RSP: 0018:ffffc90000d67968 EFLAGS: 00010246
> > > RAX: ffff88812badaa48 RBX: 0000000000000000 RCX: ffffffff840d481d
> > > RDX: 0000000000000465 RSI: 0000000000000000 RDI: 0000000000000270
> > > RBP: ffffc90000d679a8 R08: 0000000000000277 R09: 0000000000000000
> > > R10: 0001ffffffffffff R11: 0001c90000d679a8 R12: ffff88812ac03800
> > > R13: ffff88812c87c400 R14: ffff88812ae42210 R15: ffff888103026940
> > > FS: 00007f08b4e6f700(0000) GS:ffff88813bc00000(0000) knlGS:0000000000000000
> > > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > > CR2: 0000000000000270 CR3: 000000012c58b000 CR4: 00000000003506f0
> > > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > > Call Trace:
> > > <TASK>
> > > unix_diag_get_exact net/unix/diag.c:285 [inline]
> > > unix_diag_handler_dump+0x3f9/0x500 net/unix/diag.c:317
> > > __sock_diag_cmd net/core/sock_diag.c:235 [inline]
> > > sock_diag_rcv_msg+0x237/0x250 net/core/sock_diag.c:266
> > > netlink_rcv_skb+0x13e/0x250 net/netlink/af_netlink.c:2564
> > > sock_diag_rcv+0x24/0x40 net/core/sock_diag.c:277
> > > netlink_unicast_kernel net/netlink/af_netlink.c:1330 [inline]
> > > netlink_unicast+0x5e9/0x6b0 net/netlink/af_netlink.c:1356
> > > netlink_sendmsg+0x739/0x860 net/netlink/af_netlink.c:1932
> > > sock_sendmsg_nosec net/socket.c:714 [inline]
> > > sock_sendmsg net/socket.c:734 [inline]
> > > ____sys_sendmsg+0x38f/0x500 net/socket.c:2476
> > > ___sys_sendmsg net/socket.c:2530 [inline]
> > > __sys_sendmsg+0x197/0x230 net/socket.c:2559
> > > __do_sys_sendmsg net/socket.c:2568 [inline]
> > > __se_sys_sendmsg net/socket.c:2566 [inline]
> > > __x64_sys_sendmsg+0x42/0x50 net/socket.c:2566
> > > do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> > > do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
> > > entry_SYSCALL_64_after_hwframe+0x63/0xcd
> > > RIP: 0033:0x4697f9
> > > Code: f7 d8 64 89 02 b8 ff ff ff ff c3 66 0f 1f 44 00 00 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 bc ff ff ff f7 d8 64 89 01 48
> > > RSP: 002b:00007f08b4e6ec48 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
> > > RAX: ffffffffffffffda RBX: 000000000077bf80 RCX: 00000000004697f9
> > > RDX: 0000000000000000 RSI: 00000000200001c0 RDI: 0000000000000003
> > > RBP: 00000000004d29e9 R08: 0000000000000000 R09: 0000000000000000
> > > R10: 0000000000000000 R11: 0000000000000246 R12: 000000000077bf80
> > > R13: 0000000000000000 R14: 000000000077bf80 R15: 00007ffdb36bc6c0
> > > </TASK>
> > > Modules linked in:
> > > CR2: 0000000000000270
> > > ---[ end trace 0000000000000000 ]---
> > > RIP: 0010:sk_user_ns include/net/sock.h:920 [inline]
> > > RIP: 0010:sk_diag_dump_uid net/unix/diag.c:119 [inline]
> > > RIP: 0010:sk_diag_fill+0x77d/0x890 net/unix/diag.c:170
> > > Code: 89 ef e8 66 d4 2d fd c7 44 24 40 00 00 00 00 49 8d 7c 24 18 e8
> > > 54 d7 2d fd 49 8b 5c 24 18 48 8d bb 70 02 00 00 e8 43 d7 2d fd <48> 8b
> > > 9b 70 02 00 00 48 8d 7b 10 e8 33 d7 2d fd 48 8b 5b 10 48 8d
> > > RSP: 0018:ffffc90000d67968 EFLAGS: 00010246
> > > RAX: ffff88812badaa48 RBX: 0000000000000000 RCX: ffffffff840d481d
> > > RDX: 0000000000000465 RSI: 0000000000000000 RDI: 0000000000000270
> > > RBP: ffffc90000d679a8 R08: 0000000000000277 R09: 0000000000000000
> > > R10: 0001ffffffffffff R11: 0001c90000d679a8 R12: ffff88812ac03800
> > > R13: ffff88812c87c400 R14: ffff88812ae42210 R15: ffff888103026940
> > > FS: 00007f08b4e6f700(0000) GS:ffff88813bc00000(0000) knlGS:0000000000000000
> > > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > > CR2: 0000000000000270 CR3: 000000012c58b000 CR4: 00000000003506f0
> > > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > > ----------------
> > > Code disassembly (best guess):
> > > 0: 89 ef mov %ebp,%edi
> > > 2: e8 66 d4 2d fd callq 0xfd2dd46d
> > > 7: c7 44 24 40 00 00 00 movl $0x0,0x40(%rsp)
> > > e: 00
> > > f: 49 8d 7c 24 18 lea 0x18(%r12),%rdi
> > > 14: e8 54 d7 2d fd callq 0xfd2dd76d
> > > 19: 49 8b 5c 24 18 mov 0x18(%r12),%rbx
> > > 1e: 48 8d bb 70 02 00 00 lea 0x270(%rbx),%rdi
> > > 25: e8 43 d7 2d fd callq 0xfd2dd76d
> > > * 2a: 48 8b 9b 70 02 00 00 mov 0x270(%rbx),%rbx <-- trapping instruction
> > > 31: 48 8d 7b 10 lea 0x10(%rbx),%rdi
> > > 35: e8 33 d7 2d fd callq 0xfd2dd76d
> > > 3a: 48 8b 5b 10 mov 0x10(%rbx),%rbx
> > > 3e: 48 rex.W
> > > 3f: 8d .byte 0x8d
> > >
> > >
> > > Best,
> > > Wei

Next message: patchwork-bot+netdevbpf: "Re: [PATCH net-next] net: bcmgenet: Clear RGMII_LINK upon link down"
Previous message: Dave Chinner: "Re: [syzbot] kernel BUG in assfail"
In reply to: Eric Dumazet: "Re: BUG: unable to handle kernel NULL pointer dereference in sk_diag_fill"
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