Messages in this thread | | | Date | Fri, 21 Oct 2022 18:52:39 -0700 | From | Kees Cook <> | Subject | Re: [PATCH][next] net: dev: Convert sa_data to flexible array in struct sockaddr |
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On Thu, Oct 20, 2022 at 10:58:50AM +0200, Paolo Abeni wrote: > On Tue, 2022-10-18 at 02:56 -0700, Kees Cook wrote: > > [...] > > struct sockaddr { > > sa_family_t sa_family; /* address family, AF_xxx */ > > - char sa_data[14]; /* 14 bytes of protocol address */ > > + union { > > + char sa_data_min[14]; /* Minimum 14 bytes of protocol address */ > > + DECLARE_FLEX_ARRAY(char, sa_data); > > Any special reason to avoid preserving the old name for the array and > e.g. using sa_data_flex for the new field, so we don't have to touch > the sockaddr users?
Yes -- the reason is exactly to not touch the sockaddr users (who generally treat sa_data as a fake flexible array). By switching it to a flex-array the behavior will stay the same (especially under the coming -fstrict-flex-arrays option), except that it breaks sizeof(). But the broken sizeof() allows us to immediately find all the places where the code explicitly depends on sa_data being 14 bytes. And for those cases, we switch to sizeof(sa_data_min).
If we went the reverse route (and added -fstrict-flex-arrays) we might end up adding a bunch of false positives all at once, because the places that treated it as a flex-array would suddenly all begin behaving as a 14-byte array.
-- Kees Cook
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