On Thu, Nov 30, 2023 at 07:40:26PM +0100, Johannes Berg wrote: > On Thu, 2023-11-30 at 10:32 -0800, Kees Cook wrote: > > Yeah, I would expect this to mean that there is a code path that > > GCC found where the value could overflow. It does this when a variable > > "value range" gets bounded (e.g. an int isn't the full -INT_MAX to INT_MAX > > range).And flex_array_size() was designed to saturate at SIZE_MIX rather > > than wrapping around to an unexpected small value, so these are playing > > together it seems. > > > > However, I would have expected the kzalloc() to blow up _first_. > > Hmm. > > > Regardless, I suspect the addition of "if (n_thresholds > 1)" is what is > > tripping GCC. > > > > int len = nla_len(attrs[NL80211_ATTR_CQM_RSSI_THOLD]); > > ... > > return nl80211_set_cqm_rssi(info, thresholds, len / 4, > > hysteresis); > > > > Now it "knows" there is a path where n_threasholds could be [2, > > INT_MAX]. > > Yeah, it's not _really_ bounded, apart from the message length? But then > struct_size() should saturate and fail? But I guess it cannot know that, > and limits the object size to 1<<63 - 1 whereas the copy is 1<<64 - 1... > > > Does this warning go away if "len" is made unsigned? > > Thing is, neither Kalle nor I can even reproduce the warning locally, so > it's a bit hard to check ... not even with their config and gcc 12.2.0 > (nix, rather than debian though.) Ah! Hmm. Let me see if I can coax out the warning locally... -- Kees Cook
