strncpy() is deprecated for use on NUL-terminated destination strings
[1] and as such we should prefer more robust and less ambiguous string
interfaces.
This patch replaces 3 callsites of strncpy().
The first two populate the destination buffer `nsm.name` -- which we
expect to be NUL-terminated based on their use with format strings.
Firstly, as I understand it, virtio_rpmsg_announce_create() creates an
rpmsg_ns_msg and sends via:
virtio_rpmsg_bus.c:
336: err = rpmsg_sendto(rpdev->ept, &nsm, sizeof(nsm), RPMSG_NS_ADDR);
... which uses:
virtio_rpmsg_sendto() -> rpmsg_send_offchannel_raw()
... which copies its data into an rpmsg_hdr `msg` in virtio_rpmsg_bus.c
618: memcpy(msg->data, data, len);
This callback is invoked when a message is received from the remote
processor:
rpmsg_ns.c:
30: /* invoked when a name service announcement arrives */
31: static int rpmsg_ns_cb(struct rpmsg_device *rpdev, void *data, int len,
32: void *priv, u32 src)
33: {
34: struct rpmsg_ns_msg *msg = data;
...
50: /* don't trust the remote processor for null terminating the name */
51: msg->name[RPMSG_NAME_SIZE - 1] = '\0';
... which leads into the use of `name` within a format string:
rpmsg_ns.c:
57: dev_info(dev, "%sing channel %s addr 0x%x\n",
58: rpmsg32_to_cpu(rpdev, msg->flags) & RPMSG_NS_DESTROY ?
59: "destroy" : "creat", msg->name, chinfo.dst);
We can also observe that `nsm` is not zero-initialized and as such we
should maintain the NUL-padding behavior that strncpy() provides:
virtio_rpmsg_bus.c:
330: struct rpmsg_ns_msg nsm;
Considering the above, a suitable replacement is `strscpy_pad` due to
the fact that it guarantees both NUL-termination and NUL-padding on the
destination buffer.
Now, for the third and final destination buffer rpdev->id.name we can
just go for strscpy() (not _pad()) as rpdev points to &vch->rpdev:
| rpdev = &vch->rpdev;
... and vch is zero-allocated:
| vch = kzalloc(sizeof(*vch), GFP_KERNEL);
... this renders any additional NUL-byte assignments (like the ones
strncpy() or strscpy_pad() does) redundant.
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>
Link: https://lore.kernel.org/r/20231023-strncpy-drivers-rpmsg-virtio_rpmsg_bus-c-v2-1-dc591c36f5ed@google.com
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
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