On Thu, May 05, 2022 at 07:16:18PM -0400, Paul Moore wrote: > On Thu, May 5, 2022 at 2:39 PM Kees Cook <keescook@xxxxxxxxxxxx> wrote: > > 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? > > I honestly don't know, the audit userspace was hacking around it with > some header file duplication/munging last I heard, but I try to avoid > having to touch Steve's audit userspace code. > > > > 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. > > ... and for whatever it is worth, I wasn't expecting it to be a > problem either. Surprise :) > > > 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... > > I think from a practical perspective ensuring that the major IPsec/IKE > tools, e.g. the various *SWANs, that know about labeled IPSec still > build and can set/get the SA/SPD labels correctly would be sufficient. > I seriously doubt there would be any problems, but who knows. There are certainly some cases in which the transformation of zero-length arrays into flexible-array members can bring some issues to the surface[1][2]. This is the first time that we know of one of them in user-space. However, we haven't transformed the arrays in UAPI yet (with the exception of a couple of cases[3][4]). But that is something that we are planning to try soon[5]. -- Gustavo [1] https://github.com/KSPP/linux/issues?q=invalid+use+of+flexible+array [2] https://github.com/KSPP/linux/issues?q=invalid+application+of+%E2%80%98sizeof%E2%80%99+to+incomplete+type [3] https://git.kernel.org/linus/db243b796439c0caba47865564d8acd18a301d18 [4] https://git.kernel.org/linus/d6cdad870358128c1e753e6258e295ab8a5a2429 [5] https://git.kernel.org/pub/scm/linux/kernel/git/gustavoars/linux.git/commit/?h=for-next/kspp-fam0-uapi