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[119.74.6.224]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2d676408147sm23954825ad.0.2026.08.24.23.10.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 24 Aug 2026 23:10:31 -0700 (PDT) From: Wei Jie LAW <98lawweijie@gmail.com> To: Dmitry Torokhov Cc: Wei Jie Law <98lawweijie@gmail.com>, Andrew Duggan , Jiri Kosina , Benjamin Tissoires , linux-input@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: [PATCH v3 0/2] Input: synaptics-rmi4 - fix two device-controlled out-of-bounds writes Date: Tue, 25 Aug 2026 14:10:25 +0800 Message-ID: <20260825061027.105062-1-98lawweijie@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-input@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Wei Jie Law <98lawweijie@gmail.com> Hi Dmitry, While putting together a reproducer for an out-of-bounds bug in hid-rmi ([1]; a v4 fixing a hole in its own error path is being sent alongside this series) I found two further memory-safety problems in the shared RMI4 core. Both are driven entirely by data the *device* supplies -- its Page Description Table -- so they are reachable from a malicious USB HID device with no code running on the victim, and equally from I2C and SMBus RMI4 devices. Neither depends on the hid-rmi bug; they are in drivers/input/rmi4/ and need fixing separately. Both are present in mainline and in every stable tree I looked at. 1/2 is an off-by-one: RMI_PDT_INT_SOURCE_COUNT_MASK is 0x07, so interrupt_source_count can be 7, but struct rmi_function declares int irq[RMI_FN_MAX_IRQS] with RMI_FN_MAX_IRQS == 6 and two loops walk it up to fn->num_of_irqs. irq[6] is the storage of the next member, unsigned int irq_pos, so the function's position in the interrupt bitmap is silently replaced with a Linux virq number. UBSAN flags all five stores plus the read on the unregister path. 2/2 is a time-of-check/time-of-use across two reads of the device: the PDT is scanned three times and re-read from the device every time, irq_mask[] is sized by the counting scan and filled by the creating scan, and nothing verifies the two agree. KASAN catches the resulting set_bit() walking off the end of the flexible array at the tail of every struct rmi_function. 2/2 also closes the device-driven route into an older problem in rmi_create_function_irq(): irq_create_mapping() is called without checking for failure, and it returns 0, not an error code. A device that declares one interrupt in the counting scan and four in the creating scan makes the mapping fail, and irq_set_chip_data(0, fn) plus irq_set_chip_and_handler(0, &rmi_irq_chip, handle_simple_irq) then replace the chip and flow handler of IRQ 0 -- the timer, on x86: =========== /proc/interrupts, before =========== 0: 9 0 IO-APIC 2-edge timer =========== /proc/interrupts, after ============ 0: 9 0 rmi4 2 timer error: hwirq 0x1 is too large for unknown-2 WARNING: CPU: 0 PID: 56 at kernel/irq/irqdomain.c:688 irq_domain_associate_locked+0x2b4/0x390 genirq: Flags mismatch irq 0. 00002000 (rmi4-00.fn01) vs. 00215a00 (timer) With 2/2 applied the same device is rejected before any mapping is attempted and IRQ 0 is untouched. A standalone check of the irq_create_mapping() return value still looks worthwhile, but it is a separate change and I did not want to bury it in this series. How this was verified: Linux v6.12.69 (CONFIG_UBSAN_BOUNDS=y, booted slub_debug=FZPU) and v6.12.105 (CONFIG_KASAN=y + CONFIG_KASAN_INLINE=y, CONFIG_UBSAN_BOUNDS=y, booted kasan_multi_shot -- generic KASAN otherwise reports only the first error per boot), x86_64. An emulated Synaptics RMI4 device publishes a Page Description Table crafted for each case. Two independent reproducers, giving identical results: - a /dev/uhid program -- no hardware, fully deterministic, and the easy one to run; - the same device over dummy_hcd + raw-gadget with Facedancer, so the reports really traverse usbcore -> usbhid -> hid-rmi. Each bug was exercised on its own cold boot, because heap state left by a previous run changes what the out-of-bounds read returns and UBSAN reports each call site only once per boot. With both patches applied 1/2 produces no UBSAN reports and the same device -- F01 declaring the full 7 interrupt sources -- probes normally, and 2/2 fails the probe cleanly instead of corrupting the heap: three consecutive runs of the growing-PDT device give three rejections ("F40: interrupt count changed between PDT scans (pos 1 + 6 > 1)", "Function creation failed with code -22.") and zero KASAN reports, against 14 from the unpatched core on the same boot, with no kobject or refcount warnings; devices answering both scans consistently still probe and report their real product id. I am happy to post the reproducers, or to send them privately if you would rather they did not go to a public list. Changes in v3: - 2/2: reject the function *before* allocating it, rather than disposing of it afterwards. The v2 kfree() is correct on today's stable trees, but it is wrong on mainline since commit 58d42ec10b73 ("Input: rmi4 - refactor function allocation and registration"): rmi_alloc_function() has since run device_initialize() and dev_set_name() on fn->dev, so kfree() on this path would leak the name string and skip the kobject cleanup that device_initialize() obligates. put_device() is no alternative: on the pre-refactor trees the stable backports target it warns and leaks exactly as v1 did. Checking pdt->interrupt_source_count and the running total against data->irq_count before rmi_alloc_function() needs no cleanup on any tree; the error message and the -EINVAL are unchanged. - 1/2 is unchanged. Changes in v2: - 2/2: dispose of the rejected struct rmi_function with kfree() rather than put_device(). The rejection happens before rmi_register_function(), so device_initialize() has not run yet and fn->dev is still all zeroes. put_device() on it warned twice -- kobject: '(null)' (00000000cfabc269): is not initialized, yet kobject_put() is being called. WARNING: CPU: 0 PID: 9 at lib/kobject.c:734 kobject_put+0x1cf/0x4b0 refcount_t: underflow; use-after-free. WARNING: CPU: 0 PID: 9 at lib/refcount.c:28 refcount_warn_saturate+0xf2/0x150 -- and then leaked the function, because the saturated refcount stops kref_put() from ever running the release. ftrace over 405 rejections counted 810 rmi_create_function against 405 rmi_release_function, one orphan per rejection, matching a +407 growth in kmalloc-1k. With kfree() there are no warnings over 206 rejections and the slab count is flat. Thanks to the Sashiko automated review for prompting a closer look at that error path. - 1/2 is unchanged. The v1 posting is at https://lore.kernel.org/linux-input/cover.1787549234.git.98lawweijie@gmail.com/ and v2 at https://lore.kernel.org/linux-input/20260824122733.76321-1-98lawweijie@gmail.com/ [1] https://lore.kernel.org/linux-input/20260824122708.76168-1-98lawweijie@gmail.com/ Wei Jie Law (2): Input: synaptics-rmi4 - fix irq[] overrun with 7 interrupt sources Input: synaptics-rmi4 - reject a PDT that grows between scans drivers/input/rmi4/rmi_bus.h | 9 ++++++--- drivers/input/rmi4/rmi_driver.c | 19 +++++++++++++++++++ 2 files changed, 25 insertions(+), 3 deletions(-) -- 2.43.0