On Wed, May 04, 2022 at 11:14:42PM -0400, Paul Moore wrote: > On Wed, May 4, 2022 at 7:34 PM Gustavo A. R. Silva > <gustavoars@xxxxxxxxxx> wrote: > > > > Hi Paul, > > > > On Wed, May 04, 2022 at 06:57:28PM -0400, Paul Moore wrote: > > > On Tue, May 3, 2022 at 9:57 PM Kees Cook <keescook@xxxxxxxxxxxx> wrote: > > > > [..] > > > > > > +++ b/include/uapi/linux/xfrm.h > > > > @@ -31,9 +31,9 @@ struct xfrm_id { > > > > struct xfrm_sec_ctx { > > > > __u8 ctx_doi; > > > > __u8 ctx_alg; > > > > - __u16 ctx_len; > > > > + __DECLARE_FLEX_ARRAY_ELEMENTS_COUNT(__u16, ctx_len); > > > > __u32 ctx_sid; > > > > - char ctx_str[0]; > > > > + __DECLARE_FLEX_ARRAY_ELEMENTS(char, ctx_str); > > > > }; > > > > > > While I like the idea of this in principle, I'd like to hear about the > > > testing you've done on these patches. A previous flex array > > > conversion in the audit uapi headers ended up causing a problem with > > > > I'm curious about which commit caused those problems...? > > Commit ed98ea2128b6 ("audit: replace zero-length array with > flexible-array member"), however, as I said earlier, the problem was > actually with SWIG, it just happened to be triggered by the kernel > commit. There was a brief fedora-devel mail thread about the problem, > see the link below: > > * https://www.spinics.net/lists/fedora-devel/msg297991.html Wow, that's pretty weird -- it looks like SWIG was scraping the headers to build its conversions? I assume SWIG has been fixed now? > To reiterate, I'm supportive of changes like this, but I would like to > hear how it was tested to ensure there are no unexpected problems with > userspace. If there are userspace problems it doesn't mean we can't > make changes like this, it just means we need to ensure that the > userspace issues are resolved first. Well, as this is the first and only report of any problems with [0] -> [] conversions (in UAPI or anywhere) that I remember seeing, and they've been underway since at least v5.9, I hadn't been doing any new testing. So, for this case, I guess I should ask what tests you think would be meaningful here? Anything using #include should be fine: https://codesearch.debian.net/search?q=linux%2Fxfrm.h&literal=1&perpkg=1 Which leaves just this, which may be doing something weird: libabigail_2.0-1/tests/data/test-diff-filter/test-PR27569-v0.abi </data-member> <data-member access="public" layout-offset-in-bits="128"> <var-decl name="seq_hi" type-id="3f1a6b60" visibility="default" filepath="include/uapi/linux/xfrm.h" line="97" column="1"/> </data-member> <data-member access="public" layout-offset-in-bits="160"> But I see that SWIG doesn't show up in a search for linux/audit.h: https://codesearch.debian.net/search?q=linux%2Faudit.h&literal=1&perpkg=1 So this may not be a sufficient analysis... -- Kees Cook