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 tljXm23l 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bot+bpf-ci@kernel.org writes: >> >>> ``` >>> commit ec8e2e1769704b4f69261f36e6aaf035d47c5f0f >>> Author: Roman Gushchin >>> Can this dereference a NULL css pointer? The function checks css for >>> NULL at line 42 with "if (css && css_tryget(css))", which suggests css >>> can be NULL. If a BPF program calls this function with a NULL css, >>> wouldn't it crash here before reaching that check? >> >> Here css passed as an argument to bpf_get_mem_cgroup() can't be NULL, >> because the BPF verifier guarantees that it's a valid css pointer. >> >> However the result of rcu_dereference_raw(cgroup->subsys[ssid]) can be >> NULL, this is why the "if (css && css_tryget(css))" check is required >> down below. > > Yeah. Not sure how feasible it is to teach AI about KF_RCU semantics. I pulled it down locally to try and w/semcode it is properly catching this: False Positives Eliminated 1. EH-001 NULL dereference - css parameter dereferenced without check - Why false positive: BPF verifier ensures pointer parameters are non-NULL. All kernel kfuncs follow the same pattern of not checking parameters for NULL (css_rstat_updated, css_rstat_flush, bpf_put_mem_cgroup, etc.). The KF_RET_NULL flag controls return value, not parameter nullability. My plan is to just have the prompt read Documentation/bpf/kfuncs.rst, which Eduard suggested. I'll make a bpf kfuncs pattern and do that. -chris