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

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

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