netdev - Re: [PATCH net] ipv6: prevent NULL dereference in ip6

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Message-ID: <ZjuVAnjhYNomU/4J@lzaremba-mobl.ger.corp.intel.com>
Date: Wed, 8 May 2024 17:06:42 +0200
From: Larysa Zaremba <larysa.zaremba@...el.com>
To: Eric Dumazet <edumazet@...gle.com>
CC: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski
	<kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, David Ahern
	<dsahern@...nel.org>, <netdev@...r.kernel.org>, <eric.dumazet@...il.com>,
	syzbot <syzkaller@...glegroups.com>
Subject: Re: [PATCH net] ipv6: prevent NULL dereference in ip6_output()

On Tue, May 07, 2024 at 04:18:42PM +0000, Eric Dumazet wrote:
> According to syzbot, there is a chance that ip6_dst_idev()
> returns NULL in ip6_output(). Most places in IPv6 stack
> deal with a NULL idev just fine, but not here.
> 
> syzbot reported:
> 
> general protection fault, probably for non-canonical address 0xdffffc00000000bc: 0000 [#1] PREEMPT SMP KASAN PTI
> KASAN: null-ptr-deref in range [0x00000000000005e0-0x00000000000005e7]
> CPU: 0 PID: 9775 Comm: syz-executor.4 Not tainted 6.9.0-rc5-syzkaller-00157-g6a30653b604a #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
>  RIP: 0010:ip6_output+0x231/0x3f0 net/ipv6/ip6_output.c:237
> Code: 3c 1e 00 49 89 df 74 08 4c 89 ef e8 19 58 db f7 48 8b 44 24 20 49 89 45 00 49 89 c5 48 8d 9d e0 05 00 00 48 89 d8 48 c1 e8 03 <42> 0f b6 04 38 84 c0 4c 8b 74 24 28 0f 85 61 01 00 00 8b 1b 31 ff
> RSP: 0018:ffffc9000927f0d8 EFLAGS: 00010202
> RAX: 00000000000000bc RBX: 00000000000005e0 RCX: 0000000000040000
> RDX: ffffc900131f9000 RSI: 0000000000004f47 RDI: 0000000000004f48
> RBP: 0000000000000000 R08: ffffffff8a1f0b9a R09: 1ffffffff1f51fad
> R10: dffffc0000000000 R11: fffffbfff1f51fae R12: ffff8880293ec8c0
> R13: ffff88805d7fc000 R14: 1ffff1100527d91a R15: dffffc0000000000
> FS:  00007f135c6856c0(0000) GS:ffff8880b9400000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000020000080 CR3: 0000000064096000 CR4: 00000000003506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>   NF_HOOK include/linux/netfilter.h:314 [inline]
>   ip6_xmit+0xefe/0x17f0 net/ipv6/ip6_output.c:358
>   sctp_v6_xmit+0x9f2/0x13f0 net/sctp/ipv6.c:248
>   sctp_packet_transmit+0x26ad/0x2ca0 net/sctp/output.c:653
>   sctp_packet_singleton+0x22c/0x320 net/sctp/outqueue.c:783
>   sctp_outq_flush_ctrl net/sctp/outqueue.c:914 [inline]
>   sctp_outq_flush+0x6d5/0x3e20 net/sctp/outqueue.c:1212
>   sctp_side_effects net/sctp/sm_sideeffect.c:1198 [inline]
>   sctp_do_sm+0x59cc/0x60c0 net/sctp/sm_sideeffect.c:1169
>   sctp_primitive_ASSOCIATE+0x95/0xc0 net/sctp/primitive.c:73
>   __sctp_connect+0x9cd/0xe30 net/sctp/socket.c:1234
>   sctp_connect net/sctp/socket.c:4819 [inline]
>   sctp_inet_connect+0x149/0x1f0 net/sctp/socket.c:4834
>   __sys_connect_file net/socket.c:2048 [inline]
>   __sys_connect+0x2df/0x310 net/socket.c:2065
>   __do_sys_connect net/socket.c:2075 [inline]
>   __se_sys_connect net/socket.c:2072 [inline]
>   __x64_sys_connect+0x7a/0x90 net/socket.c:2072
>   do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>   do_syscall_64+0xf5/0x240 arch/x86/entry/common.c:83
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
> Fixes: 778d80be5269 ("ipv6: Add disable_ipv6 sysctl to disable IPv6 operaion on specific interface.")
> Reported-by: syzbot <syzkaller@...glegroups.com>

'Closes:' tag would be nice.

> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> ---
>  net/ipv6/ip6_output.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
> index b9dd3a66e4236fbf67af75c5f98c921b38c18bf6..8f67a43843bbf856ac706fc7cbb28cc08ea0e6d0 100644
> --- a/net/ipv6/ip6_output.c
> +++ b/net/ipv6/ip6_output.c
> @@ -234,7 +234,7 @@ int ip6_output(struct net *net, struct sock *sk, struct sk_buff *skb)
>  	skb->protocol = htons(ETH_P_IPV6);
>  	skb->dev = dev;
>  
> -	if (unlikely(READ_ONCE(idev->cnf.disable_ipv6))) {
> +	if (unlikely(!idev || READ_ONCE(idev->cnf.disable_ipv6))) {
>  		IP6_INC_STATS(net, idev, IPSTATS_MIB_OUTDISCARDS);
>  		kfree_skb_reason(skb, SKB_DROP_REASON_IPV6DISABLED);
>  		return 0;
> -- 
> 2.45.0.rc1.225.g2a3ae87e7f-goog
> 
>