CVE-2024-57889

In the Linux kernel, the following vulnerability has been resolved:

pinctrl: mcp23s08: Fix sleeping in atomic context due to regmap locking

If a device uses MCP23xxx IO expander to receive IRQs, the following bug can happen:

BUG: sleeping function called from invalid context at kernel/locking/mutex.c:283 in_atomic(): 1, irqs_disabled(): 1, non_block: 0, … preempt_count: 1, expected: 0 … Call Trace: … __might_resched+0x104/0x10e __might_sleep+0x3e/0x62 mutex_lock+0x20/0x4c regmap_lock_mutex+0x10/0x18 regmap_update_bits_base+0x2c/0x66 mcp23s08_irq_set_type+0x1ae/0x1d6 __irq_set_trigger+0x56/0x172 __setup_irq+0x1e6/0x646 request_threaded_irq+0xb6/0x160 …

We observed the problem while experimenting with a touchscreen driver which used MCP23017 IO expander (I2C).

The regmap in the pinctrl-mcp23s08 driver uses a mutex for protection from concurrent accesses, which is the default for regmaps without .fast_io, .disable_locking, etc.

mcp23s08_irq_set_type() calls regmap_update_bits_base(), and the latter locks the mutex.

However, __setup_irq() locks desc->lock spinlock before calling these functions. As a result, the system tries to lock the mutex whole holding the spinlock.

It seems, the internal regmap locks are not needed in this driver at all. mcp->lock seems to protect the regmap from concurrent accesses already, except, probably, in mcp_pinconf_get/set.

mcp23s08_irq_set_type() and mcp23s08_irq_mask/unmask() are called under chip_bus_lock(), which calls mcp23s08_irq_bus_lock(). The latter takes mcp->lock and enables regmap caching, so that the potentially slow I2C accesses are deferred until chip_bus_unlock().

The accesses to the regmap from mcp23s08_probe_one() do not need additional locking.

In all remaining places where the regmap is accessed, except mcp_pinconf_get/set(), the driver already takes mcp->lock.

This patch adds locking in mcp_pinconf_get/set() and disables internal locking in the regmap config. Among other things, it fixes the sleeping in atomic context described above.

Weakness

The product does not properly acquire or release a lock on a resource, leading to unexpected resource state changes and behaviors.

Affected Software

Extended Description

Locking is a type of synchronization behavior that ensures that multiple independently-operating processes or threads do not interfere with each other when accessing the same resource. All processes/threads are expected to follow the same steps for locking. If these steps are not followed precisely - or if no locking is done at all - then another process/thread could modify the shared resource in a way that is not visible or predictable to the original process. This can lead to data or memory corruption, denial of service, etc.

Potential Mitigations

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/25.html
• https://cwe.mitre.org/data/definitions/26.html
• https://cwe.mitre.org/data/definitions/27.html

References

• https://git.kernel.org/stable/c/0310cbad163a908d09d99c26827859365cd71fcb
• https://git.kernel.org/stable/c/788d9e9a41b81893d6bb8faa05f045c975278318
• https://git.kernel.org/stable/c/830f838589522404cd7c2f0f540602f25034af61
• https://git.kernel.org/stable/c/8c6fd5803b988a5e78c9b9e42c70a936d7cfc6ec
• https://git.kernel.org/stable/c/9372e160d8211a7e17f2abff8370794f182df785
• https://git.kernel.org/stable/c/a37eecb705f33726f1fb7cd2a67e514a15dfe693
• https://git.kernel.org/stable/c/c55d186376a87b468c9ee30f2195e0f3857f61a0