On Thu, Oct 5, 2023 at 7:54 AM Alexander Lobakin <[email protected]> wrote: > > From: Kees Cook <[email protected]> > Date: Wed, 4 Oct 2023 22:02:00 -0700 > > > On Wed, Oct 04, 2023 at 08:07:55PM -0700, Kees Cook wrote: > >> On Thu, Oct 05, 2023 at 12:30:18AM +0000, Justin Stitt wrote: > >>> `strncpy` is deprecated for use on NUL-terminated destination strings > >>> [1] and as such we should prefer more robust and less ambiguous > >>> interfaces. > >>> > >>> Let's opt for memcpy as we are copying strings into slices of length > >>> `ETH_GSTRING_LEN` within the `data` buffer. Other similar get_strings() > >>> implementations [2] [3] use memcpy(). > >>> > >>> Link: > >>> https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings > >>> [1] > >>> Link: > >>> https://elixir.bootlin.com/linux/v6.3/source/drivers/infiniband/ulp/opa_vnic/opa_vnic_ethtool.c#L167 > >>> [2] > >>> Link: > >>> https://elixir.bootlin.com/linux/v6.3/source/drivers/infiniband/ulp/ipoib/ipoib_ethtool.c#L137 > >>> [3] > >>> Link: https://github.com/KSPP/linux/issues/90 > >>> Cc: [email protected] > >>> Signed-off-by: Justin Stitt <[email protected]> > >>> --- > >>> Note: build-tested only. > >>> --- > >>> drivers/net/dsa/lan9303-core.c | 4 ++-- > >>> 1 file changed, 2 insertions(+), 2 deletions(-) > >>> > >>> diff --git a/drivers/net/dsa/lan9303-core.c > >>> b/drivers/net/dsa/lan9303-core.c > >>> index ee67adeb2cdb..665d69384b62 100644 > >>> --- a/drivers/net/dsa/lan9303-core.c > >>> +++ b/drivers/net/dsa/lan9303-core.c > >>> @@ -1013,8 +1013,8 @@ static void lan9303_get_strings(struct dsa_switch > >>> *ds, int port, > >>> return; > >>> > >>> for (u = 0; u < ARRAY_SIZE(lan9303_mib); u++) { > >>> - strncpy(data + u * ETH_GSTRING_LEN, lan9303_mib[u].name, > >>> - ETH_GSTRING_LEN); > >>> + memcpy(data + u * ETH_GSTRING_LEN, lan9303_mib[u].name, > >>> + ETH_GSTRING_LEN); > >> > >> This won't work because lan9303_mib entries aren't ETH_GSTRING_LEN-long > >> strings; they're string pointers: > >> > >> static const struct lan9303_mib_desc lan9303_mib[] = { > >> { .offset = LAN9303_MAC_RX_BRDCST_CNT_0, .name = "RxBroad", }, > >> > >> So this really does need a strcpy-family function. > >> > >> And, I think the vnic_gstrings_stats and ipoib_gstrings_stats examples > >> are actually buggy -- they're copying junk into userspace... > >> > >> I am reminded of this patch, which correctly uses strscpy_pad(): > >> https://lore.kernel.org/lkml/[email protected]/ > >> > >> I think you want to do the same here, and use strscpy_pad(). And perhaps > >> send some fixes for the other memcpy() users? > > > > Meh, I think it's not worth fixing the memcpy() users of this. This > > buggy pattern is very common, it seems: > > > > $ git grep 'data.*ETH_GSTRING_LEN' | grep memcpy | wc -l > > 47 > > We have ethtool_sprintf() precisely for the sake of filling the Ethtool > statistics names. > > BTW this weird pattern "let's make the array of our stats names of fixed > width (ETH_GSTRING_LEN), so that we could use memcpy() instead of > strcpy()" was pretty common some time ago, no idea why, as it wastes > memory for tons of \0 padding and provokes issues like the one you > noticed here.
Just sent a v2 using ethtool_sprintf(). I'd appreciate some feedback on if I used it correctly. > > > > > Thanks, > Olek [v2]: https://lore.kernel.org/r/20231005-strncpy-drivers-net-dsa-lan9303-core-c-v2-1-feb452a53...@google.com Thanks Justin
