On Fri, 2024-10-25 at 15:10 -0600, Gustavo A. R. Silva wrote: > > On 25/10/24 14:48, Johannes Berg wrote: > > On Fri, 2024-10-25 at 14:36 -0600, Gustavo A. R. Silva wrote: > > > > > > > > > > Yeah, I was actually going to mention this commit, as it's the one that introduced > > > > > that `bool radar_detected` to the flex struct. However, it wasn't obvious to me > > > > > how `struct ieee80211_chanctx_conf conf` could overwrite `radar_detected` as I didn't > > > > > see `conf->drv_priv` being accessed through `struct struct ieee80211_chanctx_conf`. > > > > > > > > You have to look at the drivers, see hwsim_clear_chanctx_magic() for > > > > example; I wonder why hwsim_check_chanctx_magic() never caught this. > > > > > > Sorry, I actually meant through `struct ieee80211_chanctx`. Something like: > > > > > > struct ieee80211_chanctx *foo; > > > ... > > > > > > foo->conf.drv_priv[i] = something; > > > > > > or > > > > > > struct bar *ptr = (void *)foo->conf->drv_priv; > > > then write something into *ptr... > > > > > > In the above cases the code will indeed overwrite `radar_detected`. > > > > Right, that's what it does though, no? Except it doesn't have, in the > > driver, "foo->conf." because mac80211 only gives it a pointer to conf, > > so it's only "conf->drv_priv" (and it's the "struct bar" example.) > > OK, so do you mean that pointer to `conf` is actually coming from > `foo->conf`? Well depends what code you're looking at? I guess we should get more concrete now. Let's say hwsim: struct hwsim_chanctx_priv { u32 magic; }; ... static inline void hwsim_set_chanctx_magic(struct ieee80211_chanctx_conf *c) { struct hwsim_chanctx_priv *cp = (void *)c->drv_priv; cp->magic = HWSIM_CHANCTX_MAGIC; } probably shouldn't be marked 'inline' now that I look at it :-) This is being called in hwsim itself, of course: static int mac80211_hwsim_add_chanctx(struct ieee80211_hw *hw, struct ieee80211_chanctx_conf *ctx) { hwsim_set_chanctx_magic(ctx); ... which is only referenced as a function pointer in the ops: static const struct ieee80211_ops mac80211_hwsim_mchan_ops = { ... .add_chanctx = mac80211_hwsim_add_chanctx, (via some macros) And that's called by mac80211: static inline int drv_add_chanctx(struct ieee80211_local *local, struct ieee80211_chanctx *ctx) { int ret = -EOPNOTSUPP; might_sleep(); lockdep_assert_wiphy(local->hw.wiphy); trace_drv_add_chanctx(local, ctx); if (local->ops->add_chanctx) ret = local->ops->add_chanctx(&local->hw, &ctx->conf); so you see that the struct ieee80211_chanctx is never passed to the driver, but instead &ctx->conf, which is the struct with the flex array for driver priv. So in this example, struct hwsim_chanctx_priv::magic overlaps the radar_detected value. (The allocation happens via chanctx_data_size.) johannes