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Thu, 27 Jul 2023 14:53:33 -0700 (PDT) Date: Thu, 27 Jul 2023 21:53:24 +0000 Mime-Version: 1.0 X-B4-Tracking: v=1; b=H4sIAFPnwmQC/6tWKk4tykwtVrJSqFYqSi3LLM7MzwNyDHUUlJIzE vPSU3UzU4B8JSMDI2MDcyNz3eL80rwU3YrUPF1jS4tkS0sj8yTjFAsloPqCotS0zAqwWdGxtbU AfC3LdVsAAAA= X-Developer-Key: i=justinstitt@google.com; a=ed25519; pk=tC3hNkJQTpNX/gLKxTNQKDmiQl6QjBNCGKJINqAdJsE= X-Developer-Signature: v=1; a=ed25519-sha256; t=1690494812; l=3106; i=justinstitt@google.com; s=20230717; h=from:subject:message-id; bh=2DV18A5LAIbHOz8+4mF5Dz/H6ijYF+f0DqJHiw+O6Z8=; b=vopO06Wm0zYSnDpTC9r5I+EsMsCZYRVtZWxLb5Dfivdpz4dFnQc4/MROOoOi/9uBOTysUrbZO B8mJVXUSQDcCy59jXa+eGsPlPBt2oonSrkqDfkKPfBHRnmLmfyW1zgm X-Mailer: b4 0.12.3 Message-ID: <20230727-sound-xen-v1-1-89dd161351f1@google.com> Subject: [PATCH] ALSA: xen-front: refactor deprecated strncpy From: Justin Stitt To: Oleksandr Andrushchenko , Jaroslav Kysela , Takashi Iwai Cc: xen-devel@lists.xenproject.org, alsa-devel@alsa-project.org, linux-kernel@vger.kernel.org, Kees Cook , Justin Stitt Message-ID-Hash: SLNOJR4VNIDVRVDUQXL2UL6J46Z4ND4U X-Message-ID-Hash: SLNOJR4VNIDVRVDUQXL2UL6J46Z4ND4U X-MailFrom: 3XefCZAsKCmQLWUVKPUVKVVIQQING.EQOCNUC-FGXGNCNUC-RTQLGEV.QTI@flex--justinstitt.bounces.google.com X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; header-match-alsa-devel.alsa-project.org-0; header-match-alsa-devel.alsa-project.org-1; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header X-Mailman-Version: 3.3.8 Precedence: list List-Id: "Alsa-devel mailing list for ALSA developers - http://www.alsa-project.org" Archived-At: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: `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 `pcm->name` or `card->driver/shortname/longname` 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 Signed-off-by: Justin Stitt Reviewed-by: Kees Cook --- sound/xen/xen_snd_front_alsa.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) --- base-commit: 57012c57536f8814dec92e74197ee96c3498d24e change-id: 20230727-sound-xen-398c9927b3d8 Best regards, -- Justin Stitt diff --git a/sound/xen/xen_snd_front_alsa.c b/sound/xen/xen_snd_front_alsa.c index db917453a473..7a3dfce97c15 100644 --- a/sound/xen/xen_snd_front_alsa.c +++ b/sound/xen/xen_snd_front_alsa.c @@ -783,7 +783,7 @@ static int new_pcm_instance(struct xen_snd_front_card_info *card_info, pcm->info_flags = 0; /* we want to handle all PCM operations in non-atomic context */ pcm->nonatomic = true; - strncpy(pcm->name, "Virtual card PCM", sizeof(pcm->name)); + strscpy(pcm->name, "Virtual card PCM", sizeof(pcm->name)); if (instance_cfg->num_streams_pb) snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_PLAYBACK, @@ -835,9 +835,9 @@ int xen_snd_front_alsa_init(struct xen_snd_front_info *front_info) goto fail; } - strncpy(card->driver, XENSND_DRIVER_NAME, sizeof(card->driver)); - strncpy(card->shortname, cfg->name_short, sizeof(card->shortname)); - strncpy(card->longname, cfg->name_long, sizeof(card->longname)); + strscpy(card->driver, XENSND_DRIVER_NAME, sizeof(card->driver)); + strscpy(card->shortname, cfg->name_short, sizeof(card->shortname)); + strscpy(card->longname, cfg->name_long, sizeof(card->longname)); ret = snd_card_register(card); if (ret < 0)