On Wed, Aug 30, 2023 at 01:22:37PM -0700, Jeff Johnson wrote: > On 8/30/2023 12:51 PM, Christian Lamparter wrote: > > Hi, > > > > On 8/29/23 15:29, Jeff Johnson wrote: > > > Currently struct ieee80211_tim_ie defines: > > > u8 virtual_map[1]; > > > > > > Per the guidance in [1] change this to be a flexible array. > > > > > > As a result of this change, adjust all related struct size tests to > > > account for the fact that the sizeof(struct ieee80211_tim_ie) now > > > accounts for the minimum size of the virtual_map. > > > > > > [1] https://docs.kernel.org/process/deprecated.html#zero-length-and-one-element-arrays > > > > > > Signed-off-by: Jeff Johnson <quic_jjohnson@xxxxxxxxxxx> > > > --- > > > diff --git a/include/linux/ieee80211.h b/include/linux/ieee80211.h > > > index bd2f6e19c357..4cdc2eb98f16 100644 > > > --- a/include/linux/ieee80211.h > > > +++ b/include/linux/ieee80211.h > > > @@ -961,7 +961,7 @@ struct ieee80211_tim_ie { > > > u8 dtim_period; > > > u8 bitmap_ctrl; > > > /* variable size: 1 - 251 bytes */ > > > - u8 virtual_map[1]; > > > + u8 virtual_map[]; > > > } __packed; > > > > > > Uhh, the 802.11 (my 2012 Version has this in) spec in > > 8.4.2.7 TIM Element demands this to be 1 - 251 bytes. > > And this is why there's a comment above... With your > > change this could be confusing. Would it be possible > > to fix that somehow? Like in a anonymous union/group > > with a flexible array and a u8? > > Adding Kees to the discussion for any advice. Yes, the virtual_map must > contain at least one octet but may contain more than one. And to complicate > matters, the information that tells us how many octets are actually present > is found outside the struct; the TLV header that precedes the struct will > contain the length of the struct, and hence the length of the bitmap is that > size - 2 (the size of the dtim_period and bitmap_ctrl fields). Bummer about the count variable being elsewhere, but we'll deal with that later. :) For the array declaration, though, yes, we can do a "minimum size 1" like this: union { u8 required_byte; DECLARE_FLEX_ARRAY(u8, virtual_map); }; -- Kees Cook
