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Mon, 14 Sep 2026 13:24:28 -0700 (PDT) Received: from remote-01 ([84.17.55.229]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-486eb34fdd2sm29328458f8f.28.2026.09.14.13.24.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 14 Sep 2026 13:24:28 -0700 (PDT) From: Aleksei Sviridkin To: netdev@vger.kernel.org Cc: chester.a.unal@arinc9.com, daniel@makrotopia.org, andrew@lunn.ch, olteanv@gmail.com, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, matthias.bgg@gmail.com, angelogioacchino.delregno@collabora.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mediatek@lists.infradead.org, Aleksei Sviridkin Subject: [PATCH net 1/2] net: dsa: mt7530: fix NULL dereference on unbind of MT7531 and MT7621 Date: Mon, 14 Sep 2026 23:24:20 +0300 Message-ID: <20260914202421.2737079-2-f@lex.la> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260914202421.2737079-1-f@lex.la> References: <20260914202421.2737079-1-f@lex.la> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The core and io supplies are only requested for ID_MT7530: both the devm_regulator_get() in probe and the regulator_enable() in mt7530_setup() are guarded by the switch id, but mt7530_remove() disables them unconditionally. On an MT7621 or an MT7531 both pointers are NULL, so rmmod or a sysfs unbind calls regulator_disable() on NULL. Fixes: ddda1ac116c8 ("net: dsa: mt7530: support the 7530 switch on the Mediatek MT7621 SoC") Signed-off-by: Aleksei Sviridkin Assisted-by: LLM --- Found by accident on a Netcraze NC-1012 (MT7981B + MT7531, 6.18.44) while looking for a way to tear a DSA port down at runtime: # echo mdio-bus:1f > /sys/bus/mdio_bus/drivers/mt7530-mdio/unbind Unable to handle kernel access to user memory outside uaccess routines at virtual address 0000000000000078 pc : regulator_disable+0x14/0x48 lr : mt7530_remove+0x1c/0x80 x0 : 0000000000000000 Call trace: regulator_disable+0x14/0x48 (P) mt7530_remove+0x1c/0x80 mdio_remove+0x20/0x40 device_release_driver_internal+0x1cc/0x220 unbind_store+0xac/0xb0 Kernel panic - not syncing: Oops: Fatal exception The oops itself is a process-context oops that kills the writing task. It became a panic and a reboot because OpenWrt's generic kernel config sets CONFIG_PANIC_ON_OOPS=y and this target does not override it, not because of anything local to this bench. With CONFIG_REGULATOR=n the stub regulator_disable() returns 0 and nothing is dereferenced at all - NET_DSA_MT7530 neither selects nor depends on REGULATOR - so the severity is config-dependent, and the commit message states the mechanism rather than an outcome. x0 is the regulator pointer and regulator_disable() reads regulator->rdev straight away, so the NULL comes from the field never being assigned rather than from an error pointer: with CONFIG_REGULATOR=y devm_regulator_get() hands back a valid pointer or an ERR_PTR, and on anything but ID_MT7530 it is never called at all. The same shape applies to MT7621, which mt7530_of_match also binds. The MMIO driver is unaffected: it makes no regulator calls at all, though it does still carry the include. The id test is used rather than a NULL check because the driver already says "these supplies belong to ID_MT7530" that way in the other two places it matters: the devm_regulator_get() pair in mt7530_probe() and the regulator_set_voltage()/regulator_enable() pair in mt7530_setup(). A NULL check would be a third spelling of the same condition. Tested on the board above. Without the patch the unbind panics as shown; both pointers come out of kzalloc and are never assigned on an MT7531, so the fault is structural rather than timing-dependent. With this patch plus the unrelated teardown fix described below, the same unbind runs to completion: mdio-bus:1f leaves /sys/bus/mdio_bus/drivers/mt7530-mdio/, lan1-lan4 disappear, the kernel prints "DSA: tree 0 torn down", and uptime does not reset. The kernel under test was identified by the sha256 of its ELF notes section, read from /sys/kernel/notes on the running board and computed in advance from the image that was flashed. dmesg is not silent across that unbind. It gains one WARN - a single cut here/WARNING/end trace block - from sysfs_remove_link() under dsa_user_destroy() reaching an already-removed netdev directory: "kernfs: can not remove 'phydev', no directory". That is a DSA teardown-ordering defect rather than a regulator one, and in this run it fired on the first unbind after boot. dmesg is where it shows: pstore gained no new record across the run, but pstore records only oopses and panics and could not have caught a WARN. That run needed one unrelated fix on top, deliberately kept out of this patch: mt7530_remove_common() frees the MDIO IRQs before dsa_unregister_switch() hands them back, and the board dies in handle_nested_irq() a few hundred milliseconds later. With this patch alone, the panic moves from regulator_disable+0x14 to that second defect, and mt7530_remove is reached at +0x24/0x90 rather than +0x1c/0x80 - which is the point: the NULL dereference is gone and execution now gets past it. That second defect is being handled separately. Not tested: the ID_MT7530 branch, which must still disable both rails. There is no MT7530 or MT7621 hardware here, so the disassembly stands in for it - before the change mt7530_remove() falls from the priv NULL check straight into ldr x0, [x19, #40] / bl regulator_disable; after it, ldr w0, [x19, #72] (priv->id) / cbz w0 gates both calls, and ID_MT7530 is 0. Built with W=1, no warnings; checkpatch --strict clean. drivers/net/dsa/mt7530-mdio.c | 18 ++++++++++-------- 1 file changed, 10 insertions(+), 8 deletions(-) diff --git a/drivers/net/dsa/mt7530-mdio.c b/drivers/net/dsa/mt7530-mdio.c index 784dd58a7158..de42f70afcfa 100644 --- a/drivers/net/dsa/mt7530-mdio.c +++ b/drivers/net/dsa/mt7530-mdio.c @@ -227,15 +227,17 @@ mt7530_remove(struct mdio_device *mdiodev) if (!priv) return; - ret = regulator_disable(priv->core_pwr); - if (ret < 0) - dev_err(priv->dev, - "Failed to disable core power: %d\n", ret); + if (priv->id == ID_MT7530) { + ret = regulator_disable(priv->core_pwr); + if (ret < 0) + dev_err(priv->dev, + "Failed to disable core power: %d\n", ret); - ret = regulator_disable(priv->io_pwr); - if (ret < 0) - dev_err(priv->dev, "Failed to disable io pwr: %d\n", - ret); + ret = regulator_disable(priv->io_pwr); + if (ret < 0) + dev_err(priv->dev, "Failed to disable io pwr: %d\n", + ret); + } mt7530_remove_common(priv); -- 2.53.0