Re: [PATCH 3/3] dmaengine: xilinx: dpdma: Reserve space for a string terminator

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

On Thu, Oct 01, 2026 at 04:50:23PM -0400, Frank Li wrote:
> On Sat, Sep 26, 2026 at 05:34:15PM +0300, Laurent Pinchart wrote:
> > On Sat, Sep 26, 2026 at 08:12:50PM +0800, Jiale Yao wrote:
> > > xilinx_dpdma_debugfs_write() allocates a buffer of size bytes, and
> > > strncpy_from_user() can fill it without a terminating NUL when the input
> > > has no NUL in the copied range. strsep() and strcasecmp() then read
> > > beyond the buffer.
> >
> > strncpy() has long been considered unsafe, and has finally been removed
> > from the kernel in v7.2. A better fix would be to similarly replace
> > strncpy_from_user() with a safe equivalent.
> 
> Do you means use strndup_user()?

I was thinking about adding a strscpy_user(), but a dup version could
possibly be interesting too if there are enough users that call
k[zm]alloc + strncpy_from_user.

> > > Allocate an extra byte and keep that byte zero-initialized, so the input
> > > copied remains unchanged and the buffer is always terminated.
> > >
> > > Fixes: 1d220435cab3 ("dmaengine: xilinx: dpdma: Add debugfs support")
> > > Signed-off-by: Jiale Yao <yaojiale02@163.com>
> > > ---
> > >  drivers/dma/xilinx/xilinx_dpdma.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/dma/xilinx/xilinx_dpdma.c b/drivers/dma/xilinx/xilinx_dpdma.c
> > > index d9a3542c4531..b61ef3062d84 100644
> > > --- a/drivers/dma/xilinx/xilinx_dpdma.c
> > > +++ b/drivers/dma/xilinx/xilinx_dpdma.c
> > > @@ -410,7 +410,7 @@ static ssize_t xilinx_dpdma_debugfs_write(struct file *f,
> > >  	if (dpdma_debugfs.testcase != DPDMA_TC_NONE)
> > >  		return -EBUSY;
> > >
> > > -	kern_buff = kzalloc(size, GFP_KERNEL);
> > > +	kern_buff = kzalloc(size + 1, GFP_KERNEL);
> > >  	if (!kern_buff)
> > >  		return -ENOMEM;
> > >  	kern_buff_start = kern_buff;

-- 
Regards,

Laurent Pinchart