[PATCH net] igmp: fix byte order in /proc/net/igmp output

[PATCH net] igmp: fix byte order in /proc/net/igmp output

[Eugene Crosser]

/proc/net/igmp is a readonly attribute that shows multicast groups
to which different network interfaces are subscribed. Among other
things, it displays `multiaddr` which is a 32 bit network-byte-order
field, in hexadecimal format. Prior to this patch, the field was
displayed as an integer, resulting in reverse byte order on little
endian architectures. This patch converts it with ntohl() for display
the same way as this is done for the /proc/net/mcfilter attribute.

The patch changes (corrects) user-visible behaviour.

Signed-off-by: Eugene Crosser <Eugene.Crosser@ru.ibm.com>
---
 net/ipv4/igmp.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
index b3086cf..f9d2139 100644
--- a/net/ipv4/igmp.c
+++ b/net/ipv4/igmp.c
@@ -2722,7 +2722,7 @@ static int igmp_mc_seq_show(struct seq_file *seq, void *v)
 		delta = im->timer.expires - jiffies;
 		seq_printf(seq,
 			   "\t\t\t\t%08X %5d %d:%08lX\t\t%d\n",
-			   im->multiaddr, im->users,
+			   ntohl(im->multiaddr), im->users,
 			   im->tm_running,
 			   im->tm_running ? jiffies_delta_to_clock_t(delta) : 0,
 			   im->reporter);
-- 
2.6.6

Re: [PATCH net] igmp: fix byte order in /proc/net/igmp output

[Eric Dumazet]

On Wed, 2016-05-04 at 14:11 +0200, Eugene Crosser wrote:
> /proc/net/igmp is a readonly attribute that shows multicast groups
> to which different network interfaces are subscribed. Among other
> things, it displays `multiaddr` which is a 32 bit network-byte-order
> field, in hexadecimal format. Prior to this patch, the field was
> displayed as an integer, resulting in reverse byte order on little
> endian architectures. This patch converts it with ntohl() for display
> the same way as this is done for the /proc/net/mcfilter attribute.
> 
> The patch changes (corrects) user-visible behaviour.
> 
> Signed-off-by: Eugene Crosser <Eugene.Crosser@ru.ibm.com>
> ---
>  net/ipv4/igmp.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
> index b3086cf..f9d2139 100644
> --- a/net/ipv4/igmp.c
> +++ b/net/ipv4/igmp.c
> @@ -2722,7 +2722,7 @@ static int igmp_mc_seq_show(struct seq_file *seq, void *v)
>  		delta = im->timer.expires - jiffies;
>  		seq_printf(seq,
>  			   "\t\t\t\t%08X %5d %d:%08lX\t\t%d\n",
> -			   im->multiaddr, im->users,
> +			   ntohl(im->multiaddr), im->users,
>  			   im->tm_running,
>  			   im->tm_running ? jiffies_delta_to_clock_t(delta) : 0,
>  			   im->reporter);


I do not believe we can change this. This is unfortunately too late.

/proc/net/tcp has the same 'issue' or if you prefer, well known
behavior.

Such change would break basically all /proc/net/igmp users.

Re: [PATCH net] igmp: fix byte order in /proc/net/igmp output

[David Miller]

From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Wed, 04 May 2016 06:13:36 -0700

> On Wed, 2016-05-04 at 14:11 +0200, Eugene Crosser wrote:
>> /proc/net/igmp is a readonly attribute that shows multicast groups
>> to which different network interfaces are subscribed. Among other
>> things, it displays `multiaddr` which is a 32 bit network-byte-order
>> field, in hexadecimal format. Prior to this patch, the field was
>> displayed as an integer, resulting in reverse byte order on little
>> endian architectures. This patch converts it with ntohl() for display
>> the same way as this is done for the /proc/net/mcfilter attribute.
>> 
>> The patch changes (corrects) user-visible behaviour.
>> 
>> Signed-off-by: Eugene Crosser <Eugene.Crosser@ru.ibm.com>
>> ---
>>  net/ipv4/igmp.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
>> index b3086cf..f9d2139 100644
>> --- a/net/ipv4/igmp.c
>> +++ b/net/ipv4/igmp.c
>> @@ -2722,7 +2722,7 @@ static int igmp_mc_seq_show(struct seq_file *seq, void *v)
>>  		delta = im->timer.expires - jiffies;
>>  		seq_printf(seq,
>>  			   "\t\t\t\t%08X %5d %d:%08lX\t\t%d\n",
>> -			   im->multiaddr, im->users,
>> +			   ntohl(im->multiaddr), im->users,
>>  			   im->tm_running,
>>  			   im->tm_running ? jiffies_delta_to_clock_t(delta) : 0,
>>  			   im->reporter);
> 
> 
> I do not believe we can change this. This is unfortunately too late.
> 
> /proc/net/tcp has the same 'issue' or if you prefer, well known
> behavior.
> 
> Such change would break basically all /proc/net/igmp users.

Agreed.

Re: [PATCH net] igmp: fix byte order in /proc/net/igmp output

[Evgeny Cherkashin]

-----Eric Dumazet <eric.dumazet@gmail.com> wrote: -----

>To: Evgeny Cherkashin/Russia/IBM@IBMRU
>From: Eric Dumazet <eric.dumazet@gmail.com>
>Date: 2016-05-04 16:13
>Cc: crosser@average.org, netdev@vger.kernel.org
>Subject: Re: [PATCH net] igmp: fix byte order in /proc/net/igmp
>output
>
>On Wed, 2016-05-04 at 14:11 +0200, Eugene Crosser wrote:
>> /proc/net/igmp is a readonly attribute that shows multicast groups
>> to which different network interfaces are subscribed. Among other
>> things, it displays `multiaddr` which is a 32 bit
>network-byte-order
>> field, in hexadecimal format. Prior to this patch, the field was
>> displayed as an integer, resulting in reverse byte order on little
>> endian architectures. This patch converts it with ntohl() for
>display
>> the same way as this is done for the /proc/net/mcfilter attribute.
>> 
>> The patch changes (corrects) user-visible behaviour.
>> 
>> Signed-off-by: Eugene Crosser <Eugene.Crosser@ru.ibm.com>
>> ---
>>  net/ipv4/igmp.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
>> index b3086cf..f9d2139 100644
>> --- a/net/ipv4/igmp.c
>> +++ b/net/ipv4/igmp.c
>> @@ -2722,7 +2722,7 @@ static int igmp_mc_seq_show(struct seq_file
>*seq, void *v)
>>  		delta = im->timer.expires - jiffies;
>>  		seq_printf(seq,
>>  			   "\t\t\t\t%08X %5d %d:%08lX\t\t%d\n",
>> -			   im->multiaddr, im->users,
>> +			   ntohl(im->multiaddr), im->users,
>>  			   im->tm_running,
>>  			   im->tm_running ? jiffies_delta_to_clock_t(delta) : 0,
>>  			   im->reporter);
>
>
>I do not believe we can change this. This is unfortunately too late.
>
>/proc/net/tcp has the same 'issue' or if you prefer, well known
>behavior.
>
>Such change would break basically all /proc/net/igmp users.

I understand that. It is unfortunate though that the byte order is not _just_ wrong, it's _different_ on BE and LE machines...
Oh well.

Thanks,

Eugene