Patchwork Bluetooth: Fix null pointer dereference in l2cap_chan_send

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Submitter Minho Ban
Date May 21, 2012, 12:58 a.m.
Message ID <4FB9932B.9070101@samsung.com>
Download mbox | patch
Permalink /patch/160301/
State Not Applicable
Delegated to: David Miller
Headers show

Comments

Minho Ban - May 21, 2012, 12:58 a.m.
If l2cap_chan_send is called will null conn it will cause kernel Oops.
This patch checks if conn is valid before entering l2cap_chan_send.

2871 [  177.271861] Unable to handle kernel NULL pointer dereference at virtual address 00000010
2872 [  177.271867] pgd = eadc0000
2873 [  177.271870] [00000010] *pgd=6ad03831, *pte=00000000, *ppte=00000000
2874 [  177.271884] Internal error: Oops: 17 [#1] PREEMPT SMP
2875 [  177.271891] Modules linked in:
2876 [  177.271900] CPU: 3    Not tainted  (3.0.15-00019-g097836e #36)
2877 [  177.271925] PC is at l2cap_chan_send+0x8c/0x6f8
2878 [  177.271933] LR is at 0xc089d59c
2879 [  177.271940] pc : [<c0531514>]    lr : [<c089d59c>]    psr: 80000013
2880 [  177.271943] sp : ddda1d50  ip : 0000035c  fp : ddda1dac
2881 [  177.271948] r10: 0000035c  r9 : 00000000  r8 : ddda1f3c
2882 [  177.271954] r7 : ed67ec00  r6 : 00000006  r5 : ed67ec00  r4 : 00000003
2883 [  177.271959] r3 : ddda1d7c  r2 : 0000035c  r1 : 00000000  r0 : ed67ec00
2884 [  177.271967] Flags: Nzcv  IRQs on  FIQs on  Mode SVC_32 ISA ARM  Segment user
2885 [  177.271973] Control: 10c5387d  Table: 6adc004a  DAC: 00000015
~~~ snip ~~~~~
3000 [  177.272989] Backtrace:
3001 [  177.273001] [<c0531488>] (l2cap_chan_send+0x0/0x6f8) from [<c053700c>] (l2cap_sock_sendmsg+0xc0/0x15c)
3002 [  177.273023] [<c0536f4c>] (l2cap_sock_sendmsg+0x0/0x15c) from [<c0458afc>] (sock_sendmsg+0xcc/0xd4)
3003 [  177.273035] [<c0458a30>] (sock_sendmsg+0x0/0xd4) from [<c0459558>] (sys_sendto+0xb8/0xdc)
3004 [  177.273041]  r9:ddda0000 r8:00004040 r7:00000000 r6:ebdf9d40 r5:0004fb00
3005 [  177.273050] r4:0000035c
3006 [  177.273059] [<c04594a0>] (sys_sendto+0x0/0xdc) from [<c045959c>] (sys_send+0x20/0x28)
3007 [  177.273077] [<c045957c>] (sys_send+0x0/0x28) from [<c00431c0>] (ret_fast_syscall+0x0/0x30)
3008 [  177.273087] Code: e5901004 e24b3030 e51ba050 e590e21c (e5914010)
3009 [  177.273096] ---[ end trace 29a418305c9cffba ]---

Signed-off-by: Minho Ban <mhban@samsung.com>
---
 net/bluetooth/l2cap_sock.c |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)
Gustavo F. Padovan - May 21, 2012, 4:17 p.m.
Hi Minho,

* Minho Ban <mhban@samsung.com> [2012-05-21 09:58:19 +0900]:

> If l2cap_chan_send is called will null conn it will cause kernel Oops.
> This patch checks if conn is valid before entering l2cap_chan_send.

chan->conn should be always valid, and if not we have a bug somewhere else in
the code and not in l2cap_chan_send(). It could be a locking problem maybe.
Also check if you can reproduce this with latest bluetooth-next.

	Gustavo
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Minho Ban - May 22, 2012, 1:21 a.m.
On 05/22/2012 01:17 AM, Gustavo Padovan wrote:
> Hi Minho,
> 
> * Minho Ban <mhban@samsung.com> [2012-05-21 09:58:19 +0900]:
> 
>> If l2cap_chan_send is called will null conn it will cause kernel Oops.
>> This patch checks if conn is valid before entering l2cap_chan_send.
> 
> chan->conn should be always valid, and if not we have a bug somewhere else in
> the code and not in l2cap_chan_send(). It could be a locking problem maybe.
> Also check if you can reproduce this with latest bluetooth-next.
> 
> 	Gustavo
> 

Thanks for comment. I'm using bluetooth-next backporting to kernel 3.0
I wonder how do we guarantee chan->conn is valid if other thread release chan->lock
just after exit l2cap_chan_del.
It seem l2cap_chan_del is well protected with various mutex (eg, sk, conn, chan) but
that may not enough to prevent lock waiters from accessing object.

Regards,
Minho Ban
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Chanyeol Park - May 22, 2012, 12:35 p.m.
Hi
On 2012년 05월 21일 09:58, Minho Ban wrote:
> If l2cap_chan_send is called will null conn it will cause kernel Oops.
> This patch checks if conn is valid before entering l2cap_chan_send.
>
> 2871 [  177.271861] Unable to handle kernel NULL pointer dereference at virtual address 00000010
> 2872 [  177.271867] pgd = eadc0000
> 2873 [  177.271870] [00000010] *pgd=6ad03831, *pte=00000000, *ppte=00000000
> 2874 [  177.271884] Internal error: Oops: 17 [#1] PREEMPT SMP
> 2875 [  177.271891] Modules linked in:
> 2876 [  177.271900] CPU: 3    Not tainted  (3.0.15-00019-g097836e #36)
> 2877 [  177.271925] PC is at l2cap_chan_send+0x8c/0x6f8
> 2878 [  177.271933] LR is at 0xc089d59c
> 2879 [  177.271940] pc : [<c0531514>]    lr : [<c089d59c>]    psr: 80000013
> 2880 [  177.271943] sp : ddda1d50  ip : 0000035c  fp : ddda1dac
> 2881 [  177.271948] r10: 0000035c  r9 : 00000000  r8 : ddda1f3c
> 2882 [  177.271954] r7 : ed67ec00  r6 : 00000006  r5 : ed67ec00  r4 : 00000003
> 2883 [  177.271959] r3 : ddda1d7c  r2 : 0000035c  r1 : 00000000  r0 : ed67ec00
> 2884 [  177.271967] Flags: Nzcv  IRQs on  FIQs on  Mode SVC_32 ISA ARM  Segment user
> 2885 [  177.271973] Control: 10c5387d  Table: 6adc004a  DAC: 00000015
> ~~~ snip ~~~~~
> 3000 [  177.272989] Backtrace:
> 3001 [  177.273001] [<c0531488>] (l2cap_chan_send+0x0/0x6f8) from [<c053700c>] (l2cap_sock_sendmsg+0xc0/0x15c)
> 3002 [  177.273023] [<c0536f4c>] (l2cap_sock_sendmsg+0x0/0x15c) from [<c0458afc>] (sock_sendmsg+0xcc/0xd4)
> 3003 [  177.273035] [<c0458a30>] (sock_sendmsg+0x0/0xd4) from [<c0459558>] (sys_sendto+0xb8/0xdc)
> 3004 [  177.273041]  r9:ddda0000 r8:00004040 r7:00000000 r6:ebdf9d40 r5:0004fb00
> 3005 [  177.273050] r4:0000035c
> 3006 [  177.273059] [<c04594a0>] (sys_sendto+0x0/0xdc) from [<c045959c>] (sys_send+0x20/0x28)
> 3007 [  177.273077] [<c045957c>] (sys_send+0x0/0x28) from [<c00431c0>] (ret_fast_syscall+0x0/0x30)
> 3008 [  177.273087] Code: e5901004 e24b3030 e51ba050 e590e21c (e5914010)
> 3009 [  177.273096] ---[ end trace 29a418305c9cffba ]---
>
> Signed-off-by: Minho Ban<mhban@samsung.com>
> ---
>   net/bluetooth/l2cap_sock.c |    6 ++++--
>   1 files changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/net/bluetooth/l2cap_sock.c b/net/bluetooth/l2cap_sock.c
> index 3bb1611..98d4541 100644
> --- a/net/bluetooth/l2cap_sock.c
> +++ b/net/bluetooth/l2cap_sock.c
> @@ -727,10 +727,12 @@ static int l2cap_sock_sendmsg(struct kiocb *iocb, struct socket *sock, struct ms
>   	if (msg->msg_flags&  MSG_OOB)
>   		return -EOPNOTSUPP;
>
> -	if (sk->sk_state != BT_CONNECTED)
> +	l2cap_chan_lock(chan);
> +	if (sk->sk_state != BT_CONNECTED || !chan->conn) {
> +		l2cap_chan_unlock(chan);
>   		return -ENOTCONN;
> +	}
>
> -	l2cap_chan_lock(chan);
>   	err = l2cap_chan_send(chan, msg, len, sk->sk_priority);
>   	l2cap_chan_unlock(chan);
>   
Beside !chan->conn condition,I think it makes sense that sk_state check 
should be moved after l2cap_chan_lock()
because sk_state could be changed due to l2cap_conn_del().

I think sk->state could be protected by l2cap_chan_lock() in the below 
procedure.

l2cap_conn_del()
->l2cap_chan_lock()
->l2cap_chan_del()
-> lock_sock()
__l2cap_sock_state_change() *
-> release_sock()
->l2cap_chan_unlock()

BR
Chanyeol Park.
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Minho Ban - May 24, 2012, 6:32 a.m.
On 05/22/2012 09:35 PM, Chanyeol Park wrote:
> Hi
> On 2012년 05월 21일 09:58, Minho Ban wrote:
>> diff --git a/net/bluetooth/l2cap_sock.c b/net/bluetooth/l2cap_sock.c
>> index 3bb1611..98d4541 100644
>> --- a/net/bluetooth/l2cap_sock.c
>> +++ b/net/bluetooth/l2cap_sock.c
>> @@ -727,10 +727,12 @@ static int l2cap_sock_sendmsg(struct kiocb *iocb, struct socket *sock, struct ms
>>       if (msg->msg_flags&  MSG_OOB)
>>           return -EOPNOTSUPP;
>>
>> -    if (sk->sk_state != BT_CONNECTED)
>> +    l2cap_chan_lock(chan);
>> +    if (sk->sk_state != BT_CONNECTED || !chan->conn) {
>> +        l2cap_chan_unlock(chan);
>>           return -ENOTCONN;
>> +    }
>>
>> -    l2cap_chan_lock(chan);
>>       err = l2cap_chan_send(chan, msg, len, sk->sk_priority);
>>       l2cap_chan_unlock(chan);
>>   
> Beside !chan->conn condition,I think it makes sense that sk_state check should be moved after l2cap_chan_lock()
> because sk_state could be changed due to l2cap_conn_del().
> 

Thanks, chan->conn condition is not necessary, move sk->sk_state != BT_CONNECTED behind chan_lock is enough.
I'll amend this patch.

Regards
Minho Ban
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Patch

diff --git a/net/bluetooth/l2cap_sock.c b/net/bluetooth/l2cap_sock.c
index 3bb1611..98d4541 100644
--- a/net/bluetooth/l2cap_sock.c
+++ b/net/bluetooth/l2cap_sock.c
@@ -727,10 +727,12 @@  static int l2cap_sock_sendmsg(struct kiocb *iocb, struct socket *sock, struct ms
 	if (msg->msg_flags & MSG_OOB)
 		return -EOPNOTSUPP;
 
-	if (sk->sk_state != BT_CONNECTED)
+	l2cap_chan_lock(chan);
+	if (sk->sk_state != BT_CONNECTED || !chan->conn) {
+		l2cap_chan_unlock(chan);
 		return -ENOTCONN;
+	}
 
-	l2cap_chan_lock(chan);
 	err = l2cap_chan_send(chan, msg, len, sk->sk_priority);
 	l2cap_chan_unlock(chan);