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Date:   Mon, 16 Oct 2023 18:42:42 +0000
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Message-ID: <20231016-strncpy-drivers-net-hamradio-baycom_epp-c-v2-1-39f72a72de30@google.com>
Subject: [PATCH v2] hamradio: replace deprecated strncpy with strscpy_pad
From:   Justin Stitt <justinstitt@google.com>
To:     Thomas Sailer <t.sailer@alumni.ethz.ch>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>
Cc:     linux-hams@vger.kernel.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org,
        Justin Stitt <justinstitt@google.com>
Content-Type: text/plain; charset="utf-8"
Precedence: bulk

strncpy() is deprecated for use on NUL-terminated destination strings
[1] and as such we should prefer more robust and less ambiguous string
interfaces.

We expect both hi.data.modename and hi.data.drivername to be
NUL-terminated based on its usage with sprintf:
|       sprintf(hi.data.modename, "%sclk,%smodem,fclk=%d,bps=%d%s",
|               bc->cfg.intclk ? "int" : "ext",
|               bc->cfg.extmodem ? "ext" : "int", bc->cfg.fclk, bc->cfg.bps,
|               bc->cfg.loopback ? ",loopback" : "");

Note that this data is copied out to userspace with:
|       if (copy_to_user(data, &hi, sizeof(hi)))
... however, the data was also copied FROM the user here:
|       if (copy_from_user(&hi, data, sizeof(hi)))

Considering the above, a suitable replacement is strscpy_pad() as it
guarantees NUL-termination on the destination buffer while also
NUL-padding (which is good+wanted behavior when copying data to
userspace).

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
Link: https://github.com/KSPP/linux/issues/90
Cc: linux-hardening@vger.kernel.org
Signed-off-by: Justin Stitt <justinstitt@google.com>
---
Changes in v2:
- use strscpy_pad (thanks Kees)
- bytes arrays are now considered "buffets" :) (thanks Kees)
- Link to v1: https://lore.kernel.org/r/20231012-strncpy-drivers-net-hamradio-baycom_epp-c-v1-1-8f4097538ee4@google.com
---
Note: build-tested only.

Also, there are 33 instances of trailing whitespace in this file alone.
I've opted to not remove them in this patch.
---
 drivers/net/hamradio/baycom_epp.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/hamradio/baycom_epp.c b/drivers/net/hamradio/baycom_epp.c
index 83ff882f5d97..ccfc83857c26 100644
--- a/drivers/net/hamradio/baycom_epp.c
+++ b/drivers/net/hamradio/baycom_epp.c
@@ -1074,7 +1074,7 @@ static int baycom_siocdevprivate(struct net_device *dev, struct ifreq *ifr,
 		return 0;
 
 	case HDLCDRVCTL_DRIVERNAME:
-		strncpy(hi.data.drivername, "baycom_epp", sizeof(hi.data.drivername));
+		strscpy_pad(hi.data.drivername, "baycom_epp", sizeof(hi.data.drivername));
 		break;
 		
 	case HDLCDRVCTL_GETMODE:
@@ -1091,7 +1091,7 @@ static int baycom_siocdevprivate(struct net_device *dev, struct ifreq *ifr,
 		return baycom_setmode(bc, hi.data.modename);
 
 	case HDLCDRVCTL_MODELIST:
-		strncpy(hi.data.modename, "intclk,extclk,intmodem,extmodem,divider=x",
+		strscpy_pad(hi.data.modename, "intclk,extclk,intmodem,extmodem,divider=x",
 			sizeof(hi.data.modename));
 		break;
 

---
base-commit: cbf3a2cb156a2c911d8f38d8247814b4c07f49a2
change-id: 20231012-strncpy-drivers-net-hamradio-baycom_epp-c-6e11c9483b9f

Best regards,
--
Justin Stitt <justinstitt@google.com>