Re: [lvc-project] [PATCH] IB/hfi1: fix buffer underflow in fault injection code

[Dennis Dalessandro <dennis.dalessandro@cornelisnetworks.com>]

On 1/15/25 2:14 PM, Fedor Pchelkin wrote:
> On Wed, 15. Jan 12:55, Dennis Dalessandro wrote:
>> On 12/27/24 6:09 PM, Vitaliy Shevtsov wrote:
>>> [Why]
>>> The fault injection code may have a buffer underflow, which may cause
>>> memory corruption by writing a newline character before the base address of
>>> the array. This can happen if the fault->opcodes bitmap is empty.
>>>
>>> Since a file in debugfs is created with an empty bitmap, it is possible to
>>> read the file before any set bits are written to it.
>>>
>>> [How]
>>> Fix this by checking that the size variable is greater than zero, otherwise
>>> return zero as the number of bytes read.
>>>
>>> Found by Linux Verification Center (linuxtesting.org) with Svace.
>>>
>>> Fixes: a74d5307caba ("IB/hfi1: Rework fault injection machinery")
>>> Signed-off-by: Vitaliy Shevtsov <v.shevtsov@maxima.ru>
>>> ---
>>>  drivers/infiniband/hw/hfi1/fault.c | 3 ++-
>>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/infiniband/hw/hfi1/fault.c b/drivers/infiniband/hw/hfi1/fault.c
>>> index ec9ee59fcf0c..2d87f9c8b89d 100644
>>> --- a/drivers/infiniband/hw/hfi1/fault.c
>>> +++ b/drivers/infiniband/hw/hfi1/fault.c
>>> @@ -190,7 +190,8 @@ static ssize_t fault_opcodes_read(struct file *file, char __user *buf,
>>>  		bit = find_next_bit(fault->opcodes, bitsize, zero);
>>>  	}
>>>  	debugfs_file_put(file->f_path.dentry);
>>> -	data[size - 1] = '\n';
>>> +	if (size)
>>> +		data[size - 1] = '\n';
>>>  	data[size] = '\0';
>>>  	ret = simple_read_from_buffer(buf, len, pos, data, size);
>>>  free_data:
>>
>> I don't think size can ever be 0. No reason to change this I don't think.
>>
>> -Denny
>>
> 
> Seems the patch description rather clearly shows the size can be zero in
> case the corresponding opcodes bitmap is empty. Which is the case when
> user reads the file before writing anything to it.

Guess it's OK then.

Acked-by: Dennis Dalessandro <dennis.dalessandro@cornelisnetworks.com>