From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=91.218.175.229 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793634053; b=YquWJOjQVOgIkNmO1KEZo+tbV0xCMJLDnLZ/SN+/9wmP3QaQAptb5hvNLcvI/tO8BTv+ hpw3BpaCntlavT8mZmFxVMpPJxi+EOzQf/Hu8P425QVVejVhGP77GwJfgteNyZYxUm+Cj lsI2nLjDUpUmigsrHwbnpXAXyaHFwTc6dZSp3jJNHprzcXGUYUTb0uiuJjj04kAVyAj7Z 0W1M2AoffjAKRs9HOBw7ByHJ+rGIo7dvoJwZgd+Un2UPx6xa4qOuHlNVFnlyOJtY4HXSC pR2Q89yZgyEB7XjXRDQfB6CAJFq6c8xD4nq4pt7DCn6I9uqxPdpQB490FSg/r1uFrvA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793634053; h=DMARC-Filter:X-Envelope-To:DKIM-Signature:X-Envelope-To:Received: X-Mizu-Trace-ID:X-Migadu-Flow:Message-ID:Date:MIME-Version:User-Agent: Subject:To:Cc:References:Content-Language:From:In-Reply-To: Content-Type:Content-Transfer-Encoding; bh=C+xl5OHF774uZtOPJCxbupJhSCVj7T1aesHy1KgIPVQ=; b=DbQBdtEm1FD935Aedxq08uorwZeInmXQCwSqXL7VRAPK1LrKPcc/hyAzZXh7I9LllOis SjeSGHQ2KektdVnQ/Neg9DuR+wG3dC7OrcHEN7owbx5k0LFNmbGxGJRA5l/+C9NTuzhJj rri9bu/9Srrs4LjNpk0M1fgbAxJJp+/1O4ZwrR5HwOelSBVzoAKO7QXp2Szdy6no3WFRB e0TOJO4g4o2xmk2yZgQG1NoncqY73A6E6Bgkvdlr58grL3hp+ptI7Ec4CldZnfR1pSMSq dh5HC5KHBXToyQ+X9WAbhxSG/w7oX8BLdE/0N+GXgCHXRXBaFR8d01yZxCFnkGCPqKw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=Befe4p1s; arc=none smtp.remote-ip=91.218.175.229 Received: from mta0.migadu.com (out-229.mta0.migadu.com [91.218.175.229]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B68F5606B91D for ; Mon, 2 Nov 2026 15:40:51 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org B68F5606B91D Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=Befe4p1s X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=2RxZ1Fiv8HmDPeSkPRWplPA67yOwGmzkE3Pmd5fIgAI=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1793634049; v=1; x=1794238849; b=Befe4p1s1dPV5wEiiN8VWowjJohaMdYgChQo2iReBi/0naWhjWv1f/cMbznBmFtJkfGK3zaW sg/iS4v9W3nC582Nm2KLjQqbGjoDmAyxg9QyG2N59s/+ESRN9/yn1H2/vz34Id+oUutKCQeOXuA JvvTAheFKUgnF0fsy75lHPxI= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 2e5b9646824930c3; Mon, 02 Nov 2026 15:40:49 +0000 X-Mizu-Trace-ID: 2e5b9646824930c3 X-Migadu-Flow: FLOW_OUT Message-ID: <0316f664-d98c-43be-92af-13c30436727a@linux.dev> Date: Mon, 2 Nov 2026 23:40:40 +0800 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 00/39] sysctl: replace overloaded extra pointers with typed bounds and context To: David Laight , Joel Granados Cc: Joel Granados , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org References: <20261029105837.2f8bee67@pumpkin> Content-Language: en-US From: Wen Yang In-Reply-To: <20261029105837.2f8bee67@pumpkin> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 10/29/26 18:58, David Laight wrote: > On Thu, 29 Oct 2026 00:34:39 +0800 > wen.yang@linux.dev wrote: > >> From: Wen Yang >> >> struct ctl_table describes an entry with data, maxlen and, until this >> series, two untyped misc pointers in extra1 and extra2. Those two pointers >> have accumulated at least seven unrelated jobs: a fixed bound, a bound read >> through a pointer on every call, an object or namespace pointer, a small >> integer cookie encoded into the pointer, a lock signal, NULL standing for >> "no bound", and a value the core itself casts to unsigned int while >> validating a u8 range. Nothing in the entry says which job applies, so >> readers infer it from the handler, and the core gets it wrong where it >> treats extra1 as an unsigned int. >> >> The numeric half of this change is the direction Eric Biederman asked for: >> >> You can still save a lot more by turning .extra1 and .extra2 >> into longs instead of keeping them as pointers and needing >> constants to be pointed at somewhere. >> >> [...] I don't see any reason why you want shared >> constants for such a handful of things. Especially when >> it has proven to be error prone in the past. >> >> min/max are plain unsigned long members, so the comparisons are ordinary >> C and cannot be confused with a pointer. The shared const arrays that only >> existed to give those pointers an address (sysctl_vals and >> sysctl_long_vals) are removed as well. >> >> The tree already records this direction. fs/proc/proc_sysctl.c documents >> extra1/extra2 as "extra pointers usable by the proc handler routines" and >> carries: >> >> XXX: we should eventually modify these to use long min / max [0] >> [0] https://lkml.kernel.org/87zgpte9o4.fsf@email.froward.int.ebiederm.org >> >> This series completes that TODO and removes the comment. >> >> priv is this series' addition: the same pair of fields also hides handler >> context, which a numeric bound cannot express, and keeping it out of data >> is what removes the restore-before-delegate pattern. >> >> The overloading is also a memory-safety hazard. The obvious alternative -- >> keep handler context in data and restore the value pointer in each handler >> -- needs an original_data field in nine addrconf and two devinet handlers; >> one missed restore turns a user-supplied integer into a write over a kernel >> pointer. nf_log reaches the same problem from the other side: it replaces >> data with a local buffer inside a single handler, so data means two things >> within one function. This revision removes that temptation instead of >> managing it. >> >> The core is not exempt. sysctl_check_table_array() reads >> *(unsigned int *)table->extra1 to validate a u8 range. That is only correct >> while every u8 entry happens to point extra1/extra2 at an int or unsigned >> int; a long bound, a context pointer or an encoded integer would be read as >> four bytes of the wrong object. No such entry exists today, so this is a >> latent class rather than a live bug, but the invariant is untyped and >> unchecked, and nf_log already encodes an integer into extra1. >> >> The refactor is the first five patches; they define the replacement >> contract and prove it covers every entry shape the tree uses today. >> >> 1. min/max hold numeric bounds by value, and priv holds handler context. >> The range converters read min/max whenever extra1 and extra2 are >> clear and keep reading the pointers while they are set, so existing >> callers keep working while they migrate and no parallel handler API or >> renamed symbol is introduced. Signed handlers read the bounds as >> signed longs, an absent endpoint is the type limit rather than NULL so >> zero stays a real bound, and a run-time range is refreshed before >> every call. Registration rejects priv on a standard handler. >> >> 2. The debug test module is converted to numeric bounds as the first >> user. >> >> 3. KUnit coverage for numeric bounds and the handlers that consume them: >> full type ranges, one-sided and zero bounds, entries without backing >> storage, explicit handlers for arrays and members, and rejection of >> writes that would partially commit. >> >> 4. KUnit coverage for run-time ranges across the scalar widths and >> jiffies, run-time bound pointers, sibling bounds, typed context, owner >> derivation, bool, registration lifecycles, and simulated per-net >> duplication. >> >> 5. KUnit coverage for priv: a standard handler must ignore it, >> registration must reject it with a standard handler, and >> re-registration must keep both the value pointer and the context. The >> same patch moves the debug module's dynamic-value entry to the >> data/priv shape. >> >> On the CTLTBL_ENTRY_* constructors: I kept the naming and argument order you >> suggested while reworking the series. As it turned out, no production table >> needed them -- the converted entries read naturally as designated >> initializers -- so I have not introduced them as a public API in this >> version; the KUnit file keeps an equivalent constructor privately, so the >> tests stay readable. I still think the public version is worth doing, and I >> would be happy to send it as a follow-up once there are real users, so the >> API and its callers can be reviewed together. >> >> Everything after patch 5 is migration and adds no new contract. Patches >> 6-32 convert the remaining users and derive owners from their backing >> storage. Patches 33-38 move handler context onto priv, one subsystem per >> patch; each of those files is touched exactly once and goes straight from >> the old pointer field to priv, with no intermediate data-as-context step. >> Patch 39 removes the extra pointers and the compatibility read. >> >> The parport conversion illustrates a concrete problem with the overloaded >> fields. In the base tree, registration overwrites the spintime minimum >> pointer in vars[0].extra1 with a port pointer. The range handler can then >> check a write against data from struct parport instead of the intended >> minimum. Moving the port context to priv and using numeric bounds also >> corrects this existing bug. A separate fix can address it independently; >> this RFC does not depend on that fix. >> >> Entries that used a *_minmax handler with neither extra pointer relied on >> NULL meaning "no bound". They now state their type limits explicitly to >> preserve that behaviour when the pointer path disappears. These include >> aio-max-nr, acpi_video_flags and nmi_wd_lpm_factor. >> >> Owners that can still be recovered from data are deliberately left alone: >> ipvs, neighbour, the fragment reassembly handlers, vsock, mptcp, rds and >> smc keep using container_of() on their backing storage. priv is only for >> entries where no such derivation exists. Mixed placement in data and priv >> was considered and rejected because it recreates the guessing problem this >> series removes. >> >> Relative to the base tree, the final state removes all 841 extra1/extra2 >> assignments across 123 files, removes the shared sysctl_vals and >> sysctl_long_vals arrays (21 references), and states bounds at each entry >> (~574 new min/max initializers) instead of pointing at constants. The >> sysctl ABI is unchanged; the parport spintime minimum is corrected as >> described above. >> >> The cost is 8 bytes per ctl_table entry on 64-bit (56 -> 64) and 4 bytes on >> 32-bit, because priv is appended; the range read path gains no indirection >> and the migrated entries no longer dereference a bound pointer. > > Can you remove the little-used 'priv' parameter by making the extra > information just follow the table entry (nested structure) and have > the relevant functions use container_of() to get the outer structure > and extra values? > Hi David, Hi Joel, I reworked the context side of the series so that priv is gone entirely; and the final tree has no per-entry context pointer. A small helper recovers the enclosing object, but it needs the slot index from the caller: #define sysctl_table_container(entry, type, member, index) ({ \ static_assert(__same_type(*(entry), \ typeof_member(type, member[0])), \ "pointer type mismatch"); \ (type *)((void *)(entry) - offsetof(type, member) - \ (size_t)(index) * sizeof(*(entry))); \ }) The reason plain container_of() is not enough is that the core keeps the table as a contiguous array. For struct addrconf_sysctl_table { struct addrconf_sysctl_ctx context; struct ctl_table table[]; }; the handler receives an interior entry, and container_of(ctl, struct addrconf_sysctl_table, table) == (char *)outer + index * sizeof(struct ctl_table) for ctl == &outer->table[index]. It only returns the outer object for index 0. Passing the index explicitly keeps the original registered entry usable: static int addrconf_sysctl_forward(const struct ctl_table *ctl, ...) { struct addrconf_sysctl_table *t = sysctl_table_container(ctl, struct addrconf_sysctl_table, table, ADDRCONF_SYSCTL_FORWARDING); const struct addrconf_sysctl_ctx *ctx = &t->context; ... } Shared handlers get one wrapper per slot; the common body does not need to know its position: #define DEVINET_CONF_WRAPPER(attr) \ static int devinet_conf_##attr(const struct ctl_table *ctl, ...) \ { \ struct devinet_sysctl_table *t = \ sysctl_table_container(ctl, \ struct devinet_sysctl_table, devinet_vars, \ IPV4_DEVCONF_##attr - 1); \ return devinet_conf_proc_common(ctl, &t->context, ...); \ } Single-entry tables simply use slot 0: struct devinet_forward_table *t = sysctl_table_container(ctl, struct devinet_forward_table, table, 0); The series is 20 commits over 134 files, with no priv at any point. If you would prefer a different shape for the helper or the wrappers, I am happy to adjust it. Thanks, Wen > David >