From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wr2-f2.google.com (mail-wr2-f2.google.com [74.125.225.66]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7DB56397E8E for ; Sun, 2 Aug 2026 23:32:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=74.125.225.66 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785713565; cv=none; b=FVPuoAzYhFA8zl3loh7+QIklrFb4td3gZpyNQ3kaBqVHGdgIgh69P4Lb3M9NNnCuBP5JJ3BPW3EfRiu5CFH+mmsbRPXUrZRlNzlHrow97GjZkrpo8ZkcIzDI9cQmsFtYGcMEuStsYsKOIN54VBk3sG9a7Wm4GaDDvOT2dfEJjvc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785713565; c=relaxed/simple; bh=dFJcQMAil6Rc6y/t5g1S2gR4M4zDnqkrhPL4MIUApg0=; h=Mime-Version:Content-Type:Date:Message-Id:To:Cc:Subject:From: References:In-Reply-To; b=fx2uEdRSQl86O8MRwq32uyS+NDHNSRBehVINRJc45Zux15BxtlZEn0Vi/svFRKMzVvJYWtQHMZi4l6MB0gwBarxkPMwkhjF4T8O+MzPNmOGn/ccs6a/6Dj1YKnFvnTEdnPnWRRwh6xkNCiuwTVvL3R77j3MeYeUdKqNrjlgd8gE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=ax8bQ1xY; arc=none smtp.client-ip=74.125.225.66 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="ax8bQ1xY" Received: by mail-wr2-f2.google.com with SMTP id ffacd0b85a97d-470713a9053so806180f8f.0 for ; Sun, 02 Aug 2026 16:32:28 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1785713547; x=1786318347; darn=vger.kernel.org; h=in-reply-to:references:from:subject:cc:to:message-id:date :content-type:content-transfer-encoding:mime-version:from:to:cc :subject:date:message-id:reply-to:content-type; bh=Wuve+ygXJV5dqDNQOvrNoXCyKoiwGqRf0o6QCP7Pj5E=; b=ax8bQ1xYBhjLsBwDYruD3cX8/vFLfnNykwubARwGVFU4GpRQGTdojcel/RfnAtW8zb kyvl32Qv+z3rHwAfClKIOOlreKdWEAgu+pq2jhIP3J6bZMb2T66YABHZIFzob2CmgDiC HYkfWX63yoG7t5Q9pesklur09zMeTnCojnEHTOZ9x4iUOXGNY+JJI8ESN+//oVXb2TPH BSwZZ7kGBVtak2SbUedTtWVNr9zdWD4hvBkw04DoBSZRPEZhrIv/WtS6hahAz5r9sLpd wOuAKNrKZAPu4ITi3gwBQ+v/tdkbCKeQc+i17fNpk+O1cWgYyMNwcLNxzd+l0GTYExOA TqTg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1785713547; x=1786318347; h=in-reply-to:references:from:subject:cc:to:message-id:date :content-type:content-transfer-encoding:mime-version:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=Wuve+ygXJV5dqDNQOvrNoXCyKoiwGqRf0o6QCP7Pj5E=; b=duSlUO7BuaFKTiai8+xsNergoRuj1b7eQiVk2M6qJt8TLYwjVNTvlD0vviZ062kNOW DrJkSmuLTCouWlLcwLVLEI/3102NqHZCeeRalx+pCgNP+782qLojlpiAfzOF/j4b7Uuo xkjgmfaKBq4+1WDzfnUDVza6VYUNxqiTjwTiWkrSB2/58enR8b31Q8pNr9oDwoGWeKU+ Xl5uqboIp4GBsOWCVZKUB49fclupKE8huHk4/DOFXXjAgGPU+CcZiMJfTikZZVKS44yj cznFK3cmiOtt3l70I0ZfnB+IjHijaYTGNF+yLgUWuUmByGFcE8qiLy19kIKVxI+Jq19t wxsA== X-Forwarded-Encrypted: i=1; AHgh+RoohCHHAGn0jO5jB/HWZXcdtCcQlKzm5ymA+QtQQ8TN3dK++krxiNHbjMUtj+GsGEWVLBCISmmycvCY9hAYJko=@vger.kernel.org X-Gm-Message-State: AOJu0YylGCmlZOpITWmrteY6aPAeY97+fOdMoM6qtSKWPq7W6/7hgzGm WxK9VqYD8IHmHNfqY5L2rJ4Bl/juKjQMZ7JONOLo1nNgoolKxzvTxH/3 X-Gm-Gg: AR+sD12kWm02dk2NcdQQ1DeIYKGGNzxJNzs3X9PUwsvgNiQYrCKZ8wN1Qt0IkonXJoB Ti8T39enO2Pe0LBFUeYE4gv4KwamwDz4qEvTJHeWyPftkZqapSwoBMZiirpppcIt5Iy32albJp2 dfxrHLqYGT691eTcpkwAduCmEVAlGVFcTifVutWxyVBsbKwqmja88pSIgav/fKv+1JWz4xLrgy1 SOe6CtIrF0EtJ/OfwChEm9JSfCKPnPSR2xi/Gd/px2gfBXnF2osWOYvpMJj64Q1EKsq252tce6z LkPQia+ZPZZuIg8TGe/5lRUuaFFTt8uVAriqjrOyTVUrkt5KnqF00ZJBB4UJWZIp3ZwnB2yXdPZ AcsaYtkCE73MKDZ1VqSm3gWA2RTUVeINuthmMQtHeHwZjx7MOg2KSByADlossJb8WLy6FeHbtWd mdlZtbbM9ghuheIuykAfgucWgHPdKMvbpweUYjFQtnUW5uEFX/5Isqs89kdJfl0MBkShTqc8hHe FW+tMT5bpwreVYFJ4Ns0As2J2MfGfnvJGRYPyyGWi0CJwUnAlXgv2wMY8qchwr/lMpjLjfgd6Cv Lw9CEZsCCHKaSNDyNjTA7bAooG4= X-Received: by 2002:a05:600d:8492:b0:496:c2fd:1731 with SMTP id 5b1f17b1804b1-4980c64b96dmr114476095e9.1.1785713546677; Sun, 02 Aug 2026 16:32:26 -0700 (PDT) Received: from localhost (nat-icclus-192-26-29-3.epfl.ch. [192.26.29.3]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49807b5f007sm166475845e9.6.2026.08.02.16.32.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 02 Aug 2026 16:32:26 -0700 (PDT) Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Mon, 03 Aug 2026 01:32:26 +0200 Message-Id: To: "Ning Ding" , Cc: , , , , , , , , , , , , , Subject: Re: [PATCH bpf] bpf: Reject writes through untrusted allocated pointers From: "Kumar Kartikeya Dwivedi" X-Mailer: aerc 0.21.0 References: <20260726021304.97ED91F000E9@smtp.kernel.org> <20260728033837.1466123-1-dingning04@gmail.com> In-Reply-To: <20260728033837.1466123-1-dingning04@gmail.com> On Tue Jul 28, 2026 at 5:38 AM CEST, Ning Ding wrote: > A kptr loaded under an RCU read lock has MEM_ALLOC set. After > bpf_rcu_read_unlock(), the verifier marks it PTR_UNTRUSTED, but > check_ptr_to_btf_access() still allows writes because > type_is_ptr_alloc_obj() ignores that flag. > > Reject writes through MEM_ALLOC pointers that are PTR_UNTRUSTED. Reads > remain allowed and are converted to probe-memory accesses. > > Also skip the owning-reference check for these pointers, since they no > longer have a live reference after leaving the RCU critical section. > > Add verifier tests for the rejected write and permitted read cases. > > Fixes: 503e4def5414 ("bpf: Replace open code with for allocated object ch= eck") > Closes: https://lore.kernel.org/all/20260726021304.97ED91F000E9@smtp.kern= el.org/ > Assisted-by: Codex:gpt-5.6-sol > Signed-off-by: Ning Ding > --- Same comment for this one, split kernel and selftests into separate patches= . > kernel/bpf/verifier.c | 6 +- > .../bpf/progs/local_kptr_stash_fail.c | 58 +++++++++++++++++++ > 2 files changed, 62 insertions(+), 2 deletions(-) > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > index 7aa47342dc65..24c151ad2e62 100644 > --- a/kernel/bpf/verifier.c > +++ b/kernel/bpf/verifier.c > @@ -5804,13 +5804,15 @@ static int check_ptr_to_btf_access(struct bpf_ver= ifier_env *env, > * program allocated objects (which always have id > 0), > * but not for untrusted PTR_TO_BTF_ID | MEM_ALLOC. > */ > - if (atype !=3D BPF_READ && !type_is_ptr_alloc_obj(reg->type)) { > + if (atype !=3D BPF_READ && > + (!type_is_ptr_alloc_obj(reg->type) || reg->type & PTR_UNTRUSTED)) = { > verbose(env, "only read is supported\n"); > return -EACCES; > } There is a PTR_UNTRUSTED check already earlier in this function, why is tha= t not working or not enough? pw-bot: cr > > if (type_is_alloc(reg->type) && !type_is_non_owning_ref(reg->type) && > - !(reg->type & MEM_RCU) && !reg_is_referenced(env, reg)) { > + !(reg->type & (MEM_RCU | PTR_UNTRUSTED)) && > + !reg_is_referenced(env, reg)) { > verifier_bug(env, "allocated object must have a referenced id"); > return -EFAULT; > } > diff --git a/tools/testing/selftests/bpf/progs/local_kptr_stash_fail.c b/= tools/testing/selftests/bpf/progs/local_kptr_stash_fail.c > index fcf7a7567da2..d7b8cd6458bb 100644 > --- a/tools/testing/selftests/bpf/progs/local_kptr_stash_fail.c > +++ b/tools/testing/selftests/bpf/progs/local_kptr_stash_fail.c > @@ -8,14 +8,22 @@ > #include "../bpf_experimental.h" > #include "bpf_misc.h" > > +extern void bpf_rcu_read_lock(void) __ksym; > +extern void bpf_rcu_read_unlock(void) __ksym; > + > struct node_data { > long key; > long data; > struct bpf_rb_node node; > }; > > +struct plain_data { > + long key; > +}; > + > struct map_value { > struct node_data __kptr *node; > + struct plain_data __kptr *plain; > }; > > struct node_data2 { > @@ -31,6 +39,7 @@ struct node_data2 { > * [35] TYPE_TAG 'kptr_ref' type_id=3D34 > */ > struct node_data *just_here_because_btf_bug; > +struct plain_data *just_here_because_btf_bug2; > > struct { > __uint(type, BPF_MAP_TYPE_ARRAY); > @@ -82,4 +91,53 @@ long drop_rb_node_off(void *ctx) > return 0; > } > > +SEC("?tc") > +__failure __msg("only read is supported") > +long write_untrusted_alloc_obj(void *ctx) > +{ > + struct map_value *mapval; > + struct node_data *res; > + int idx =3D 0; > + > + mapval =3D bpf_map_lookup_elem(&some_nodes, &idx); > + if (!mapval) > + return 1; > + > + bpf_rcu_read_lock(); > + res =3D mapval->node; > + if (!res) { > + bpf_rcu_read_unlock(); > + return 2; > + } > + barrier_var(res); > + bpf_rcu_read_unlock(); > + > + res->key =3D 42; > + return 0; > +} > + > +SEC("?tc") > +__success > +long read_untrusted_alloc_obj(void *ctx) > +{ > + struct map_value *mapval; > + struct plain_data *res; > + int idx =3D 0; > + > + mapval =3D bpf_map_lookup_elem(&some_nodes, &idx); > + if (!mapval) > + return 1; > + > + bpf_rcu_read_lock(); > + res =3D mapval->plain; > + if (!res) { > + bpf_rcu_read_unlock(); > + return 2; > + } > + barrier_var(res); > + bpf_rcu_read_unlock(); > + > + return res->key; > +} > + > char _license[] SEC("license") =3D "GPL";