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

[Frank Li <Frank.li@oss.nxp.com>]

On Sat, Oct 03, 2026 at 06:09:58PM +0800, jiale yao wrote:
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>
> At 2026-10-02 05:00:21, "Laurent Pinchart" <laurent.pinchart@ideasonboard.com> wrote:
> >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.
>
> Thanks for all reviews, how about this one?
> https://lore.kernel.org/all/20261003095922.575350-1-yaojiale02@163.com/

Looks good.

Frank

> >
> >> > > 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