Re: [PATCH v1 net] udplite: Fix NULL pointer dereference in __sk_mem_raise_allocated().

From: Paolo Abeni <pabeni@redhat.com>
To: Kuniyuki Iwashima <kuniyu@amazon.com>,
	"David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>
Cc: Kuniyuki Iwashima <kuni1840@gmail.com>,
	netdev@vger.kernel.org,
	 syzbot+444ca0907e96f7c5e48b@syzkaller.appspotmail.com
Subject: Re: [PATCH v1 net] udplite: Fix NULL pointer dereference in __sk_mem_raise_allocated().
Date: Thu, 25 May 2023 10:59:09 +0200	[thread overview]
Message-ID: <048c84aacfe650e6602c266ff52625798fbcaa62.camel@redhat.com> (raw)
In-Reply-To: <20230523163305.66466-1-kuniyu@amazon.com>

On Tue, 2023-05-23 at 09:33 -0700, Kuniyuki Iwashima wrote:
> syzbot reported [0] a null-ptr-deref in sk_get_rmem0() while using
> IPPROTO_UDPLITE (0x88):
> 
>   14:25:52 executing program 1:
>   r0 = socket$inet6(0xa, 0x80002, 0x88)
> 
> We had a similar report [1] for probably sk_memory_allocated_add()
> in __sk_mem_raise_allocated(), and commit c915fe13cbaa ("udplite: fix
> NULL pointer dereference") fixed it by setting .memory_allocated for
> udplite_prot and udplitev6_prot.
> 
> To fix the variant, we need to set either .sysctl_wmem_offset or
> .sysctl_rmem.
> 
> Now UDP and UDPLITE share the same value for .memory_allocated, so we
> use the same .sysctl_wmem_offset for UDP and UDPLITE.
> 
> [0]:
> general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] PREEMPT SMP KASAN
> KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
> CPU: 0 PID: 6829 Comm: syz-executor.1 Not tainted 6.4.0-rc2-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/28/2023
> RIP: 0010:sk_get_rmem0 include/net/sock.h:2907 [inline]
> RIP: 0010:__sk_mem_raise_allocated+0x806/0x17a0 net/core/sock.c:3006
> Code: c1 ea 03 80 3c 02 00 0f 85 23 0f 00 00 48 8b 44 24 08 48 8b 98 38 01 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 da 48 c1 ea 03 <0f> b6 14 02 48 89 d8 83 e0 07 83 c0 03 38 d0 0f 8d 6f 0a 00 00 8b
> RSP: 0018:ffffc90005d7f450 EFLAGS: 00010246
> RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffffc90004d92000
> RDX: 0000000000000000 RSI: ffffffff88066482 RDI: ffffffff8e2ccbb8
> RBP: ffff8880173f7000 R08: 0000000000000005 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000030000
> R13: 0000000000000001 R14: 0000000000000340 R15: 0000000000000001
> FS:  0000000000000000(0000) GS:ffff8880b9800000(0063) knlGS:00000000f7f1cb40
> CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
> CR2: 000000002e82f000 CR3: 0000000034ff0000 CR4: 00000000003506f0
> Call Trace:
>  <TASK>
>  __sk_mem_schedule+0x6c/0xe0 net/core/sock.c:3077
>  udp_rmem_schedule net/ipv4/udp.c:1539 [inline]
>  __udp_enqueue_schedule_skb+0x776/0xb30 net/ipv4/udp.c:1581
>  __udpv6_queue_rcv_skb net/ipv6/udp.c:666 [inline]
>  udpv6_queue_rcv_one_skb+0xc39/0x16c0 net/ipv6/udp.c:775
>  udpv6_queue_rcv_skb+0x194/0xa10 net/ipv6/udp.c:793
>  __udp6_lib_mcast_deliver net/ipv6/udp.c:906 [inline]
>  __udp6_lib_rcv+0x1bda/0x2bd0 net/ipv6/udp.c:1013
>  ip6_protocol_deliver_rcu+0x2e7/0x1250 net/ipv6/ip6_input.c:437
>  ip6_input_finish+0x150/0x2f0 net/ipv6/ip6_input.c:482
>  NF_HOOK include/linux/netfilter.h:303 [inline]
>  NF_HOOK include/linux/netfilter.h:297 [inline]
>  ip6_input+0xa0/0xd0 net/ipv6/ip6_input.c:491
>  ip6_mc_input+0x40b/0xf50 net/ipv6/ip6_input.c:585
>  dst_input include/net/dst.h:468 [inline]
>  ip6_rcv_finish net/ipv6/ip6_input.c:79 [inline]
>  NF_HOOK include/linux/netfilter.h:303 [inline]
>  NF_HOOK include/linux/netfilter.h:297 [inline]
>  ipv6_rcv+0x250/0x380 net/ipv6/ip6_input.c:309
>  __netif_receive_skb_one_core+0x114/0x180 net/core/dev.c:5491
>  __netif_receive_skb+0x1f/0x1c0 net/core/dev.c:5605
>  netif_receive_skb_internal net/core/dev.c:5691 [inline]
>  netif_receive_skb+0x133/0x7a0 net/core/dev.c:5750
>  tun_rx_batched+0x4b3/0x7a0 drivers/net/tun.c:1553
>  tun_get_user+0x2452/0x39c0 drivers/net/tun.c:1989
>  tun_chr_write_iter+0xdf/0x200 drivers/net/tun.c:2035
>  call_write_iter include/linux/fs.h:1868 [inline]
>  new_sync_write fs/read_write.c:491 [inline]
>  vfs_write+0x945/0xd50 fs/read_write.c:584
>  ksys_write+0x12b/0x250 fs/read_write.c:637
>  do_syscall_32_irqs_on arch/x86/entry/common.c:112 [inline]
>  __do_fast_syscall_32+0x65/0xf0 arch/x86/entry/common.c:178
>  do_fast_syscall_32+0x33/0x70 arch/x86/entry/common.c:203
>  entry_SYSENTER_compat_after_hwframe+0x70/0x82
> RIP: 0023:0xf7f21579
> Code: b8 01 10 06 03 74 b4 01 10 07 03 74 b0 01 10 08 03 74 d8 01 00 00 00 00 00 00 00 00 00 00 00 00 00 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 90 90 90 8d b4 26 00 00 00 00 8d b4 26 00 00 00 00
> RSP: 002b:00000000f7f1c590 EFLAGS: 00000282 ORIG_RAX: 0000000000000004
> RAX: ffffffffffffffda RBX: 00000000000000c8 RCX: 0000000020000040
> RDX: 0000000000000083 RSI: 00000000f734e000 RDI: 0000000000000000
> RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000296 R12: 0000000000000000
> R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
>  </TASK>
> Modules linked in:
> 
> Link: https://lore.kernel.org/netdev/CANaxB-yCk8hhP68L4Q2nFOJht8sqgXGGQO2AftpHs0u1xyGG5A@mail.gmail.com/ [1]
> Fixes: 850cbaddb52d ("udp: use it's own memory accounting schema")

Thanks for addressing this issue!

The patch LGTM. 

Side note: the blamed commit is almost 7y old and the oops should not
that hard to reproduce by a real app using UDP-lite, but only syzkaller
stumbled upon it.

The above looks like a serious hint UDP-lite is not used by anyone
anymore ?!? Perhaps we could consider deprecating and dropping it? It
could simplify the UDP code a bit removing a bunch of conditionals in
fast-path, and that  nowadays would be possibly more relevant?!?

Cheers,

Paolo