Re: [PATCH 03/11] staging: replace weird strncpy() with memcpy()

Dan Carpenter
2024-04-08T15:59:53Z

On Mon, Apr 08, 2024 at 04:45:55PM +0200, Arnd Bergmann wrote:
> On Thu, Mar 28, 2024, at 17:35, Dan Carpenter wrote:
> > On Thu, Mar 28, 2024 at 03:04:47PM +0100, Arnd Bergmann wrote:
> >> This partially reverts an earlier bugfix that replaced the original
> >> incorrect memcpy() with a less bad strncpy(), but it now also avoids
> >> the original overflow.
> >>
> >> Fixes: 88a5b39b69ab ("staging/rts5208: Fix read overflow in memcpy")
> >
> > I don't see a problem with this commit. The "sendbytes - 8" prevents
> > a write overflow to buf, and the strncpy() prevents read overflow from
> > inquiry_string.
>
> I agree the commit did not introduce a runtime bug, but it did
> introduce a warning about the string being truncated.
>
> >> diff --git a/drivers/staging/rts5208/rtsx_scsi.c b/drivers/staging/rts5208/rtsx_scsi.c
> >> index 08bd768ad34d..a73b0959f5a9 100644
> >> --- a/drivers/staging/rts5208/rtsx_scsi.c
> >> +++ b/drivers/staging/rts5208/rtsx_scsi.c
> >> @@ -523,7 +523,7 @@ static int inquiry(struct scsi_cmnd *srb, struct rtsx_chip *chip)
> >>
> >> if (sendbytes > 8) {
> >> memcpy(buf, inquiry_buf, 8);
> >> - strncpy(buf + 8, inquiry_string, sendbytes - 8);
> >> + memcpy(buf + 8, inquiry_string, min(sendbytes, 36) - 8);
> >
> > I think your math is off. The string is 29 characters + NUL. So it
> > should be "min(sendbytes, 38) - 8". You're chopping off the space and
> > the NUL terminator.
> >
> > This only affects pro_formatter_flag code...
>
> The extra two bytes were clearly a mistake in the original version
> at the time it got added to drivers/staging. Note how the code
> immediately below it would overwrite the space and NUL byte again:
>
> if (pro_formatter_flag) {
> if (sendbytes > 36)
> memcpy(buf + 36, formatter_inquiry_str, sendbytes - 36);
> }
>

Ah. Okay. Fair enough.

I do think this code is really suspect... What is the point of allowing
sendbytes < 36? But that's not related to your patch.

regards,
dan carpenter