netdev - Re: [PATCH] net: tcp: check skb is non-NULL for exact match on lookups

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Date:   Wed, 2 Nov 2016 21:13:51 +0100
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     David Ahern <dsa@...ulusnetworks.com>
Cc:     netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH] net: tcp: check skb is non-NULL for exact match on lookups

I can confirm that this fixes the null-ptr-deref I've been getting.

Tested-by: Andrey Konovalov <andreyknvl@...gle.com>

On Wed, Nov 2, 2016 at 8:08 PM, David Ahern <dsa@...ulusnetworks.com> wrote:
> Andrey reported the following error report while running the syzkaller
> fuzzer:
>
> general protection fault: 0000 [#1] SMP KASAN
> Dumping ftrace buffer:
>    (ftrace buffer empty)
> Modules linked in:
> CPU: 0 PID: 648 Comm: syz-executor Not tainted 4.9.0-rc3+ #333
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> task: ffff8800398c4480 task.stack: ffff88003b468000
> RIP: 0010:[<ffffffff83091106>]  [<     inline     >]
> inet_exact_dif_match include/net/tcp.h:808
> RIP: 0010:[<ffffffff83091106>]  [<ffffffff83091106>]
> __inet_lookup_listener+0xb6/0x500 net/ipv4/inet_hashtables.c:219
> RSP: 0018:ffff88003b46f270  EFLAGS: 00010202
> RAX: 0000000000000004 RBX: 0000000000004242 RCX: 0000000000000001
> RDX: 0000000000000000 RSI: ffffc90000e3c000 RDI: 0000000000000054
> RBP: ffff88003b46f2d8 R08: 0000000000004000 R09: ffffffff830910e7
> R10: 0000000000000000 R11: 000000000000000a R12: ffffffff867fa0c0
> R13: 0000000000004242 R14: 0000000000000003 R15: dffffc0000000000
> FS:  00007fb135881700(0000) GS:ffff88003ec00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000020cc3000 CR3: 000000006d56a000 CR4: 00000000000006f0
> Stack:
>  0000000000000000 000000000601a8c0 0000000000000000 ffffffff00004242
>  424200003b9083c2 ffff88003def4041 ffffffff84e7e040 0000000000000246
>  ffff88003a0911c0 0000000000000000 ffff88003a091298 ffff88003b9083ae
> Call Trace:
>  [<ffffffff831100f4>] tcp_v4_send_reset+0x584/0x1700 net/ipv4/tcp_ipv4.c:643
>  [<ffffffff83115b1b>] tcp_v4_rcv+0x198b/0x2e50 net/ipv4/tcp_ipv4.c:1718
>  [<ffffffff83069d22>] ip_local_deliver_finish+0x332/0xad0
> net/ipv4/ip_input.c:216
> ...
>
> MD5 has a code path that calls __inet_lookup_listener with a null skb,
> so inet{6}_exact_dif_match needs to check skb against null before pulling
> the flag.
>
> Fixes: a04a480d4392 ("net: Require exact match for TCP socket lookups if
>        dif is l3mdev")
> Reported-by: Andrey Konovalov <andreyknvl@...gle.com>
> Signed-off-by: David Ahern <dsa@...ulusnetworks.com>
> ---
> Dave: commit a04a480d4392 was queued for stable, so this needs to follow it.
>
>  include/linux/ipv6.h | 2 +-
>  include/net/tcp.h    | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h
> index ca1ad9ebbc92..a0649973ee5b 100644
> --- a/include/linux/ipv6.h
> +++ b/include/linux/ipv6.h
> @@ -149,7 +149,7 @@ static inline bool inet6_exact_dif_match(struct net *net, struct sk_buff *skb)
>  {
>  #if defined(CONFIG_NET_L3_MASTER_DEV)
>         if (!net->ipv4.sysctl_tcp_l3mdev_accept &&
> -           ipv6_l3mdev_skb(IP6CB(skb)->flags))
> +           skb && ipv6_l3mdev_skb(IP6CB(skb)->flags))
>                 return true;
>  #endif
>         return false;
> diff --git a/include/net/tcp.h b/include/net/tcp.h
> index 5b82d4d94834..304a8e17bc87 100644
> --- a/include/net/tcp.h
> +++ b/include/net/tcp.h
> @@ -805,7 +805,7 @@ static inline bool inet_exact_dif_match(struct net *net, struct sk_buff *skb)
>  {
>  #if IS_ENABLED(CONFIG_NET_L3_MASTER_DEV)
>         if (!net->ipv4.sysctl_tcp_l3mdev_accept &&
> -           ipv4_l3mdev_skb(TCP_SKB_CB(skb)->header.h4.flags))
> +           skb && ipv4_l3mdev_skb(TCP_SKB_CB(skb)->header.h4.flags))
>                 return true;
>  #endif
>         return false;
> --
> 2.1.4
>