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[192.26.29.3]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49cee7fec25sm143818985e9.13.2026.09.03.23.37.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 03 Sep 2026 23:37:02 -0700 (PDT) From: Kumar Kartikeya Dwivedi To: bpf@vger.kernel.org Cc: Nicholas Carlini , Ning Ding , Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , Eduard Zingerman , Emil Tsalapatis , kkd@meta.com, kernel-team@meta.com Subject: [PATCH bpf v1 7/8] bpf: Reject untrusted allocated-object pointers Date: Fri, 4 Sep 2026 08:36:45 +0200 Message-ID: <20260904063650.3877826-8-memxor@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260904063650.3877826-1-memxor@gmail.com> References: <20260904063650.3877826-1-memxor@gmail.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=1928; i=memxor@gmail.com; h=from:subject; bh=O0xbawAqnBylYPa9BBYqUadEoCJXb0J5+JGJNj8vDJk=; b=owGbwMvMwCXmrmtenRyi38x4Wi2JIWtW2uWnZetvbmi1eTnh6ZKWjydXmNavumCckH/Yur7I/ eLC6U81OkpZGMS4GGTFFFlK/u9jMj5R+TvQdhk3zBxWJpAhDFycAjCRm/MZGZbs1UyZpnqrVWLv /ruV9rM7fabZnXv7OWdlX/0K0Xky5vsYGVaftph70uHLdZn5gjKqOf9+Jr1fGpy6Z+Kqn8sY+Q3 6//EBAA== X-Developer-Key: i=memxor@gmail.com; a=openpgp; fpr=B34BD741DE8494B76E2F717880EF20021D46C59B Content-Transfer-Encoding: 8bit From: Ning Ding When the final RCU read-side critical section ends, a local kptr is demoted to PTR_UNTRUSTED but retains MEM_ALLOC. The pointer may be NULL or may refer to an object whose lifetime is no longer protected. type_is_ptr_alloc_obj() nevertheless recognizes any PTR_TO_BTF_ID with MEM_ALLOC as a live allocated object. In particular, a refcount-only local kptr never carries NON_OWN_REF, so it still passes the bpf_refcount_acquire() argument check after RCU protection ends. The kfunc can then dereference NULL or stale memory. Make type_is_ptr_alloc_obj() reject PTR_UNTRUSTED pointers. Since type_is_non_owning_ref() is based on the same predicate, graph kfunc arguments obey the same live-object requirement. Fault-protected reads of the demoted pointer remain valid: writes are already rejected, and read fixups use bpf_may_fault_on_deref() rather than this predicate. Fixes: 1b12171533a9 ("bpf: Mark direct ld of stashed bpf_{rb,list}_node as non-owning ref") Reported-by: Nicholas Carlini Suggested-by: Nicholas Carlini Signed-off-by: Ning Ding [ kkd: Rewrote commit log ] Signed-off-by: Kumar Kartikeya Dwivedi --- include/linux/bpf_verifier.h | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h index 1339c2f028db..36b65797877d 100644 --- a/include/linux/bpf_verifier.h +++ b/include/linux/bpf_verifier.h @@ -1381,7 +1381,9 @@ static inline bool bpf_type_has_unsafe_modifiers(u32 type) static inline bool type_is_ptr_alloc_obj(u32 type) { - return base_type(type) == PTR_TO_BTF_ID && type_flag(type) & MEM_ALLOC; + return base_type(type) == PTR_TO_BTF_ID && + type_flag(type) & MEM_ALLOC && + !(type_flag(type) & PTR_UNTRUSTED); } static inline bool type_is_non_owning_ref(u32 type) -- 2.53.0