| Message ID | 20230727-sound-usb-bcd2000-v1-1-0dc73684b2f0@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | ALSA: bcd2000: refactor deprecated strncpy | expand |
On Fri, 28 Jul 2023 00:09:29 +0200, Justin Stitt wrote: > > `strncpy` is deprecated for use on NUL-terminated destination strings [1]. > > A suitable replacement is `strscpy` [2] due to the fact that it > guarantees NUL-termination on its destination buffer argument which is > _not_ always the case for `strncpy`! > > It should be noted that, in this case, the destination buffer has a > length strictly greater than the source string. Moreover, the source > string is NUL-terminated (and so is the destination) which means there > was no real bug happening here. Nonetheless, this patch would get us one > step closer to eliminating the `strncpy` API in the kernel, as its use > is too ambiguous. We need to favor less ambiguous replacements such as: > strscpy, strscpy_pad, strtomem and strtomem_pad (amongst others). > > Technically, my patch yields subtly different behavior. The original > implementation with `strncpy` would fill the entire destination buffer > with null bytes [3] while `strscpy` will leave the junk, uninitialized > bytes trailing after the _mandatory_ NUL-termination. So, if somehow > `card->driver` or `card->shortname` require this NUL-padding behavior > then `strscpy_pad` should be used. My interpretation, though, is that > the aforementioned fields are just fine as NUL-terminated strings. > Please correct my assumptions if needed and I'll send in a v2. > > [1]: www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings > [2]: manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html > [3]: https://linux.die.net/man/3/strncpy > > Link: https://github.com/KSPP/linux/issues/90 > Link: https://lore.kernel.org/r/20230727-sound-xen-v1-1-89dd161351f1@google.com (related ALSA patch) > Signed-off-by: Justin Stitt <justinstitt@google.com> Applied now. Thanks. Takashi
diff --git a/sound/usb/bcd2000/bcd2000.c b/sound/usb/bcd2000/bcd2000.c index 7aec0a95c609..392b4d8e9e76 100644 --- a/sound/usb/bcd2000/bcd2000.c +++ b/sound/usb/bcd2000/bcd2000.c @@ -395,8 +395,8 @@ static int bcd2000_probe(struct usb_interface *interface, snd_card_set_dev(card, &interface->dev); - strncpy(card->driver, "snd-bcd2000", sizeof(card->driver)); - strncpy(card->shortname, "BCD2000", sizeof(card->shortname)); + strscpy(card->driver, "snd-bcd2000", sizeof(card->driver)); + strscpy(card->shortname, "BCD2000", sizeof(card->shortname)); usb_make_path(bcd2k->dev, usb_path, sizeof(usb_path)); snprintf(bcd2k->card->longname, sizeof(bcd2k->card->longname), "Behringer BCD2000 at %s",
`strncpy` is deprecated for use on NUL-terminated destination strings [1]. A suitable replacement is `strscpy` [2] due to the fact that it guarantees NUL-termination on its destination buffer argument which is _not_ always the case for `strncpy`! It should be noted that, in this case, the destination buffer has a length strictly greater than the source string. Moreover, the source string is NUL-terminated (and so is the destination) which means there was no real bug happening here. Nonetheless, this patch would get us one step closer to eliminating the `strncpy` API in the kernel, as its use is too ambiguous. We need to favor less ambiguous replacements such as: strscpy, strscpy_pad, strtomem and strtomem_pad (amongst others). Technically, my patch yields subtly different behavior. The original implementation with `strncpy` would fill the entire destination buffer with null bytes [3] while `strscpy` will leave the junk, uninitialized bytes trailing after the _mandatory_ NUL-termination. So, if somehow `card->driver` or `card->shortname` require this NUL-padding behavior then `strscpy_pad` should be used. My interpretation, though, is that the aforementioned fields are just fine as NUL-terminated strings. Please correct my assumptions if needed and I'll send in a v2. [1]: www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [2]: manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [3]: https://linux.die.net/man/3/strncpy Link: https://github.com/KSPP/linux/issues/90 Link: https://lore.kernel.org/r/20230727-sound-xen-v1-1-89dd161351f1@google.com (related ALSA patch) Signed-off-by: Justin Stitt <justinstitt@google.com> --- sound/usb/bcd2000/bcd2000.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) --- base-commit: 57012c57536f8814dec92e74197ee96c3498d24e change-id: 20230727-sound-usb-bcd2000-400b3060a9f9 Best regards, -- Justin Stitt <justinstitt@google.com>