PNP: replace deprecated strncpy() with memcpy()

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

After having precisely calculated the lengths and ensuring we don't
overflow the buffer, this really decays to just a memcpy. Let's not use
a C string api as it makes the intention of the code confusing.

It'd be nice to use strscpy() in this case (as we clearly want
NUL-termination) because it'd clean up the code a bit. However, I don't
quite know enough about what is going on here to justify a drop-in
replacement -- too much bit magic and why (PNP_NAME_LEN - 2)? I'm afraid
using strscpy() may result in copying too many or too few bytes into our
dev->name buffer resulting in different behavior. At least using
memcpy() we can ensure the behavior is exactly the same.

Side note:
NUL-padding is not required because insert_device() calls
pnpbios_parse_data_stream() with a zero-allocated `dev`:
299 |  static int __init insert_device(struct pnp_bios_node *node) {
...
312 |  dev = pnp_alloc_dev(&pnpbios_protocol, node->handle, id);
...
316 |  pnpbios_parse_data_stream(dev, node);

then pnpbios_parse_data_stream() calls pnpbios_parse_compatible_ids().

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings
Link: https://github.com/KSPP/linux/issues/90
Signed-off-by: Justin Stitt <justinstitt@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

diff --git a/drivers/pnp/pnpbios/rsparser.c b/drivers/pnp/pnpbios/rsparser.c
index 2f31b212b1a50c9c0d4f2a15847dda93ff13c867..70af7821d3fa41273edff7c7e29a328a8118d0d1 100644 (file)
--- a/drivers/pnp/pnpbios/rsparser.c
+++ b/drivers/pnp/pnpbios/rsparser.c
@@ -454,8 +454,8 @@ static unsigned char *pnpbios_parse_compatible_ids(unsigned char *p,
                switch (tag) {
 
                case LARGE_TAG_ANSISTR:
-                       strncpy(dev->name, p + 3,
-                               len >= PNP_NAME_LEN ? PNP_NAME_LEN - 2 : len);
+                       memcpy(dev->name, p + 3,
+                              len >= PNP_NAME_LEN ? PNP_NAME_LEN - 2 : len);
                        dev->name[len >=
                                  PNP_NAME_LEN ? PNP_NAME_LEN - 1 : len] = '\0';
                        break;