[OpenWrt-Devel] [PATCH] [netifd] vlan: Array out of bounds in snprintf for vlans

[Daniel F. Dickinson]

On 31/01/18 06:20 AM, Paul Oranje wrote:
> Why use a hard coded value 4 in "snprintf(devnum, 4, "%d", vldev->id);" ?
> Paul

Max value for a VLAN id is 4095 = 4 digits, although probably better 
would be to accept full length for int and truncate in the next line.

That and this was a quick hack to get around a compile error with GCC 
2.7 (because of the buffer overrun), and not a fully formed patch; as 
stated, in the message this was more informational.

I suppose I should find some time and energy and submit a fully formed 
patch, unless someone gets there first.

Regards,

Daniel

> 
>> Op 30 jan. 2018, om 19:16 heeft cshored at thecshore.com het volgende geschreven:
>>
>> From: "Daniel F. Dickinson" <cshored at thecshore.com>
>>
>> Detected during a side project.  Not a brilliant fix, but it
>> gets the job done for now.  *very* lightly tested, more
>> for your information than anything else.
>>
>> Array out-of-bounds condition can occur because vlan
>> device name is constructed from device name (size IFNAMSIZ)
>> plus the ASCII decimal representation of the vlan id plus
>> a dot, but the target can only be IFNAMSIZ.  We fix this
>> by using fields widths (and make sure we don't truncate
>> more of the orogin device name than we must).
>>
>> Signed-off-by: Daniel F. Dickinson <cshored at thecshore.com>
>> ---
>> vlan.c | 11 +++++++++--
>> 1 file changed, 9 insertions(+), 2 deletions(-)
>>
>> diff --git a/vlan.c b/vlan.c
>> index 067f624..44852f4 100644
>> --- a/vlan.c
>> +++ b/vlan.c
>> @@ -63,10 +63,17 @@ static int vlan_set_device_state(struct device *dev, bool up)
>>
>> static void vlan_dev_set_name(struct vlan_device *vldev, struct device *dev)
>> {
>> -	char name[IFNAMSIZ];
>> +	char name[IFNAMSIZ + 1];
>> +	char devnum[5];
>> +	int i, j = 0;
>>
>> 	vldev->dev.hidden = dev->hidden;
>> -	snprintf(name, IFNAMSIZ, "%s.%d", dev->ifname, vldev->id);
>> +	snprintf(devnum, 4, "%d", vldev->id);
>> +	i = strnlen(devnum, 4);
>> +	j = IFNAMSIZ - i;
>> +	strncpy(name, dev->ifname, j);
>> +	strncat(name, ".", 1);
>> +	strncat(name, devnum, i);
>> 	device_set_ifname(&vldev->dev, name);
>> }
>>
>> -- 
>> 2.11.0
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> 
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