On 7/27/2023 12:34 AM, Kees Cook wrote:
On Wed, Jul 26, 2023 at 09:12:18PM +0000, justinstitt@xxxxxxxxxx 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_ the case for `strncpy`!
It was pretty difficult, in this case, to try and figure out whether or
not the destination buffer was zero-initialized. If it is and this
behavior is relied on then perhaps `strscpy_pad` is the preferred
option here.
Kees was able to help me out and identify the following code snippet
which seems to show that the destination buffer is zero-initialized.
| skl = devm_kzalloc(&pci->dev, sizeof(*skl), GFP_KERNEL);
With this information, I opted for `strscpy` since padding is seemingly
not required.
We did notice that str_elem->string is 44 bytes, but
skl->lib_info[ref_count].name is 128 bytes. If str_elem->string isn't
NUL-terminated, this can still hit an over-read condition (though
CONFIG_FORTIFY_SOURCE would have caught it both before with strncpy()
and now with strscpy()). So I assume it is expected to be
NUL-terminated?
Yes it is a filename of additional library which can be loaded, topology
UAPI only allows for passing 44 bytes long strings per string token (see
snd_soc_tplg_vendor_array -> union -> string flex array ->
snd_soc_tplg_vendor_string_elem -> SNDRV_CTL_ELEM_ID_NAME_MAXLEN), so we
could also change length of
skl->lib_info[ref_count].name and potentially save few bytes. And
looking at it again I also think that we should not copy destination
size number of bytes, by which I mean
ARRAY_SIZE(skl->lib_info[ref_count].name), which is 128 in this case...
so either need to change destination buffer size to be same as topology
field or calculate it differently.
