Re: [PATCH 1/3] netfilter: Fix copy_to_user too small size parametre.

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Hi Pablo.

copy_to_user( dest, source, length)

Normally,  'length'  is equal to  'sizeof (source) '.

In this case "length"   =   32
       "sizeof(source)"  =   29.

Is it intentional ?
Won't it copy extra 3 bytes of kernel data to userspace ?



regards
santosh



On Thu, Mar 1, 2012 at 3:48 PM, Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx> wrote:
> On Thu, Mar 01, 2012 at 02:46:30PM +0530, santosh nayak wrote:
>> From: Santosh Nayak <santoshprasadnayak@xxxxxxxxx>
>>
>> While copying to userspace, the size of source is 29byte where as
>> size parametre is 32 byte.  Its leaking extra-information from
>> kernel space to user space.
>> Replace EBT_FUNCTION_MAXNAMELEN by XT_EXTENSION_MAXNAMELEN.
>
> There's no information leak.
>
> Let me clarify this. Have a look at /linux/netfilter/x_tables.h, then
> you find:
>
> #define XT_FUNCTION_MAXNAMELEN 30
> #define XT_EXTENSION_MAXNAMELEN 29
> #define XT_TABLE_MAXNAMELEN 32
>
> For iptables, everything has been 30 bytes, but we stole one
> byte to store the revision field for matches/targets.
>
> For ebtables, there's no revision field and the length of the
> table name is different.
>
> But linux/netfilter/in ebtables.h, you'll find:
>
> #define EBT_TABLE_MAXNAMELEN 32
> #define EBT_CHAIN_MAXNAMELEN EBT_TABLE_MAXNAMELEN
> #define EBT_FUNCTION_MAXNAMELEN EBT_TABLE_MAXNAMELEN
>
> Note that someone decided to use 32 bytes for the ebtables
> tables/match/target name instead of 30 bytes in iptables.
>
> Yes, it sucks a bit we have to live with these interfaces until
> we have some netlink interface for all these things.
>
>> Signed-off-by: Santosh Nayak <santoshprasadnayak@xxxxxxxxx>
>> ---
>>  net/bridge/netfilter/ebtables.c |    6 +++---
>>  1 files changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/net/bridge/netfilter/ebtables.c b/net/bridge/netfilter/ebtables.c
>> index 5864cc4..f3fcbd9 100644
>> --- a/net/bridge/netfilter/ebtables.c
>> +++ b/net/bridge/netfilter/ebtables.c
>> @@ -1335,7 +1335,7 @@ static inline int ebt_make_matchname(const struct ebt_entry_match *m,
>>      const char *base, char __user *ubase)
>>  {
>>       char __user *hlp = ubase + ((char *)m - base);
>> -     if (copy_to_user(hlp, m->u.match->name, EBT_FUNCTION_MAXNAMELEN))
>> +     if (copy_to_user(hlp, m->u.match->name, XT_EXTENSION_MAXNAMELEN))
>>               return -EFAULT;
>>       return 0;
>>  }
>> @@ -1344,7 +1344,7 @@ static inline int ebt_make_watchername(const struct ebt_entry_watcher *w,
>>      const char *base, char __user *ubase)
>>  {
>>       char __user *hlp = ubase + ((char *)w - base);
>> -     if (copy_to_user(hlp , w->u.watcher->name, EBT_FUNCTION_MAXNAMELEN))
>> +     if (copy_to_user(hlp , w->u.watcher->name, XT_EXTENSION_MAXNAMELEN))
>>               return -EFAULT;
>>       return 0;
>>  }
>> @@ -1368,7 +1368,7 @@ ebt_make_names(struct ebt_entry *e, const char *base, char __user *ubase)
>>       ret = EBT_WATCHER_ITERATE(e, ebt_make_watchername, base, ubase);
>>       if (ret != 0)
>>               return ret;
>> -     if (copy_to_user(hlp, t->u.target->name, EBT_FUNCTION_MAXNAMELEN))
>> +     if (copy_to_user(hlp, t->u.target->name, XT_EXTENSION_MAXNAMELEN))
>>               return -EFAULT;
>>       return 0;
>>  }
>> --
>> 1.7.4.4
>>
>> --
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