Subject: Re: [PATCH] sysctl: fix min/max handling in __do_proc_doulongvec_minmax()

From: [email-masked] (Eric W. Biederman)
Date: Thu, 07 Oct 2010 12:38:22 -0700

Andrew Morton <[email-masked]> writes:

> On Thu, 07 Oct 2010 18:59:03 +0200
> Eric Dumazet <[email-masked]> wrote:

>> Thats fine by me, thanks Eric.
>> 
>> Andrew, please remove previous patch from your tree and replace it by
>> following one :
>> 
>> [PATCH v2] sysctl: fix min/max handling in __do_proc_doulongvec_minmax()
>> 
>> When proc_doulongvec_minmax() is used with an array of longs,
>> and no min/max check requested (.extra1 or .extra2 being NULL), we
>> dereference a NULL pointer for the second element of the array.
>> 
>> Noticed while doing some changes in network stack for the "16TB problem"
>> 
>> Fix is to not change min & max pointers in
>> __do_proc_doulongvec_minmax(), so that all elements of the vector share
>> an unique min/max limit, like proc_dointvec_minmax().
>> 
>> Signed-off-by: Eric Dumazet <[email-masked]>
>> ---
>>  kernel/sysctl.c |    2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
>> index f88552c..8e45451 100644
>> --- a/kernel/sysctl.c
>> +++ b/kernel/sysctl.c
>> @@ -2485,7 +2485,7 @@ static int __do_proc_doulongvec_minmax(void *data, struct ctl_table *table, int
>>  		kbuf[left] = 0;
>>  	}
>>  
>> -	for (; left && vleft--; i++, min++, max++, first=0) {
>> +	for (; left && vleft--; i++, first=0) {
>>  		unsigned long val;
>>  
>>  		if (write) {
>
> Did we check to see whether any present callers are passing in pointers
> to arrays of min/max values?

In 2.6.36 there are not any callers that pass in a vector of anything, I
don't know about linux-next.  It looks to me like incrementing min and
max was simply a bug.

> I wonder if there's any documentation for this interface which just
> became wrong.

Or it just became right.  Clearly no one has been expecting min
and max to be vectors.

Eric