net/dccp: null-ptr-deref in dccp_v4_rcv/selinux_socket_sock_rcv_skb

[Andrey Konovalov]

Hi,

I've got the following error report while running the syzkaller fuzzer:

IPv4: Attempt to release alive inet socket ffff880068e98940
kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] SMP KASAN
Modules linked in:
CPU: 1 PID: 3905 Comm: a.out Not tainted 4.9.0-rc3+ #333
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
task: ffff88006b9e0000 task.stack: ffff880068770000
RIP: 0010:[<ffffffff819ead5f>] [<ffffffff819ead5f>]
selinux_socket_sock_rcv_skb+0xff/0x6a0 security/selinux/hooks.c:4639
RSP: 0018:ffff8800687771c8 EFLAGS: 00010202
RAX: ffff88006b9e0000 RBX: 1ffff1000d0eee3f RCX: 1ffff1000d1d312a
RDX: 1ffff1000d1d31a6 RSI: dffffc0000000000 RDI: 0000000000000010
RBP: ffff880068777360 R08: 0000000000000000 R09: 0000000000000002
R10: dffffc0000000000 R11: 0000000000000006 R12: ffff880068e98940
R13: 0000000000000002 R14: ffff880068777338 R15: 0000000000000000
FS: 00007f00ff760700(0000) GS:ffff88006cd00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020008000 CR3: 000000006a308000 CR4: 00000000000006e0
Stack:
ffff8800687771e0 ffffffff812508a5 ffff8800686f3168 0000000000000007
ffff88006ac8cdfc ffff8800665ea500 0000000041b58ab3 ffffffff847b5480
ffffffff819eac60 ffff88006b9e0860 ffff88006b9e0868 ffff88006b9e07f0
Call Trace:
[<ffffffff819c8dd5>] security_sock_rcv_skb+0x75/0xb0 security/security.c:1317
[<ffffffff82c2a9e7>] sk_filter_trim_cap+0x67/0x10e0 net/core/filter.c:81
[<ffffffff82b81e60>] __sk_receive_skb+0x30/0xa00 net/core/sock.c:460
[<ffffffff838bbf12>] dccp_v4_rcv+0xdb2/0x1910 net/dccp/ipv4.c:873
[<ffffffff83069d22>] ip_local_deliver_finish+0x332/0xad0
net/ipv4/ip_input.c:216
[< inline >] NF_HOOK_THRESH ./include/linux/netfilter.h:232
[< inline >] NF_HOOK ./include/linux/netfilter.h:255
[<ffffffff8306abd2>] ip_local_deliver+0x1c2/0x4b0 net/ipv4/ip_input.c:257
[< inline >] dst_input ./include/net/dst.h:507
[<ffffffff83068500>] ip_rcv_finish+0x750/0x1c40 net/ipv4/ip_input.c:396
[< inline >] NF_HOOK_THRESH ./include/linux/netfilter.h:232
[< inline >] NF_HOOK ./include/linux/netfilter.h:255
[<ffffffff8306b82f>] ip_rcv+0x96f/0x12f0 net/ipv4/ip_input.c:487
[<ffffffff82bd9fb7>] __netif_receive_skb_core+0x1897/0x2a50 net/core/dev.c:4213
[<ffffffff82bdb19a>] __netif_receive_skb+0x2a/0x170 net/core/dev.c:4251
[<ffffffff82bdb493>] netif_receive_skb_internal+0x1b3/0x390 net/core/dev.c:4279
[<ffffffff82bdb6b8>] netif_receive_skb+0x48/0x250 net/core/dev.c:4303
[<ffffffff8241fc75>] tun_get_user+0xbd5/0x28a0 drivers/net/tun.c:1308
[<ffffffff82421b5a>] tun_chr_write_iter+0xda/0x190 drivers/net/tun.c:1332
[< inline >] new_sync_write fs/read_write.c:499
[<ffffffff8151bd44>] __vfs_write+0x334/0x570 fs/read_write.c:512
[<ffffffff8151f85b>] vfs_write+0x17b/0x500 fs/read_write.c:560
[< inline >] SYSC_write fs/read_write.c:607
[<ffffffff81523184>] SyS_write+0xd4/0x1a0 fs/read_write.c:599
[<ffffffff83fc02c1>] entry_SYSCALL_64_fastpath+0x1f/0xc2
arch/x86/entry/entry_64.S:209
Code: 31 45 84 c0 74 0a 41 80 f8 01 0f 8e 26 04 00 00 49 8d 7f 10 49
ba 00 00 00 00 00 fc ff df 45 0f b7 6c 24 10 49 89 f9 49 c1 e9 03 <47>
0f b6 1c 11 45 84 db 74 0a 41 80 fb 03 0f 8e 01 04 00 00 41
RIP [<ffffffff819ead5f>] selinux_socket_sock_rcv_skb+0xff/0x6a0
security/selinux/hooks.c:4639
RSP <ffff8800687771c8>
---[ end trace 6c39677dc406a11b ]---
Kernel panic - not syncing: Fatal exception in interrupt
Kernel Offset: disabled
---[ end Kernel panic - not syncing: Fatal exception in interrupt

On commit 0c183d92b20b5c84ca655b45ef57b3318b83eb9e (Oct 31).

Thanks!

[Eric Dumazet]

Please try the following patch, thanks !

diff --git a/include/net/sock.h b/include/net/sock.h
index 73c6b008f1b7..92b269709b9a 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1596,11 +1596,11 @@ static inline void sock_put(struct sock *sk)
void sock_gen_put(struct sock *sk);

int __sk_receive_skb(struct sock *sk, struct sk_buff *skb, const int nested,
- unsigned int trim_cap);
+ unsigned int trim_cap, bool refcounted);
static inline int sk_receive_skb(struct sock *sk, struct sk_buff *skb,
const int nested)
{
- return __sk_receive_skb(sk, skb, nested, 1);
+ return __sk_receive_skb(sk, skb, nested, 1, true);
}

static inline void sk_tx_queue_set(struct sock *sk, int tx_queue)
diff --git a/net/core/sock.c b/net/core/sock.c
index df171acfe232..5e3ca414357e 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -453,7 +453,7 @@ int sock_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
EXPORT_SYMBOL(sock_queue_rcv_skb);

int __sk_receive_skb(struct sock *sk, struct sk_buff *skb,
- const int nested, unsigned int trim_cap)
+ const int nested, unsigned int trim_cap, bool refcounted)
{
int rc = NET_RX_SUCCESS;

@@ -487,7 +487,8 @@ int __sk_receive_skb(struct sock *sk, struct sk_buff *skb,

bh_unlock_sock(sk);
out:
- sock_put(sk);
+ if (refcounted)
+ sock_put(sk);
return rc;
discard_and_relse:
kfree_skb(skb);
diff --git a/net/dccp/ipv4.c b/net/dccp/ipv4.c
index 345a3aeb8c7e..dff7cfab1da4 100644
--- a/net/dccp/ipv4.c
+++ b/net/dccp/ipv4.c
@@ -868,7 +868,7 @@ static int dccp_v4_rcv(struct sk_buff *skb)
goto discard_and_relse;
nf_reset(skb);

- return __sk_receive_skb(sk, skb, 1, dh->dccph_doff * 4);
+ return __sk_receive_skb(sk, skb, 1, dh->dccph_doff * 4, refcounted);

no_dccp_socket:
if (!xfrm4_policy_check(NULL, XFRM_POLICY_IN, skb))
diff --git a/net/dccp/ipv6.c b/net/dccp/ipv6.c
index 3828f94b234c..09c4e19aa285 100644
--- a/net/dccp/ipv6.c
+++ b/net/dccp/ipv6.c
@@ -738,7 +738,8 @@ static int dccp_v6_rcv(struct sk_buff *skb)
if (!xfrm6_policy_check(sk, XFRM_POLICY_IN, skb))
goto discard_and_relse;

- return __sk_receive_skb(sk, skb, 1, dh->dccph_doff * 4) ? -1 : 0;
+ return __sk_receive_skb(sk, skb, 1, dh->dccph_doff * 4,
+ refcounted) ? -1 : 0;

no_dccp_socket:
if (!xfrm6_policy_check(NULL, XFRM_POLICY_IN, skb))

[Andrey Konovalov]

Hi Eric,

Your patch fixes the issue.

Tested-by: Andrey Konovalov <andre...@google.com>

Thanks!

[Eric Dumazet]

From: Eric Dumazet <edum...@google.com>

Andrey Konovalov reported following error while fuzzing with syzkaller :

It turns out DCCP calls __sk_receive_skb(), and this broke when
lookups no longer took a reference on listeners.

Fix this issue by adding a @refcounted parameter to __sk_receive_skb(),
so that sock_put() is used only when needed.

Fixes: 3b24d854cb35 ("tcp/dccp: do not touch listener sk_refcnt under synflood")
Signed-off-by: Eric Dumazet <edum...@google.com>
Reported-by: Andrey Konovalov <andre...@google.com>
Tested-by: Andrey Konovalov <andre...@google.com>
---

[David Miller]

From: Eric Dumazet <eric.d...@gmail.com>
Date: Wed, 02 Nov 2016 17:14:41 -0700

> From: Eric Dumazet <edum...@google.com>
>
> Andrey Konovalov reported following error while fuzzing with syzkaller :

...

> It turns out DCCP calls __sk_receive_skb(), and this broke when
> lookups no longer took a reference on listeners.
>
> Fix this issue by adding a @refcounted parameter to __sk_receive_skb(),
> so that sock_put() is used only when needed.
>
> Fixes: 3b24d854cb35 ("tcp/dccp: do not touch listener sk_refcnt under synflood")
> Signed-off-by: Eric Dumazet <edum...@google.com>
> Reported-by: Andrey Konovalov <andre...@google.com>
> Tested-by: Andrey Konovalov <andre...@google.com>

Applied and queued up for -stable.