CVE-2024-57889 pinctrl: mcp23s08: Fix sleeping in atomic context due to regmap locking
A locking bug in the MCP23s08 pinctrl driver causes a kernel panic when handling IRQs, leading to system denial of service.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2024-57889?
CVE-2024-57889 is a medium-severity denial of service vulnerability in Linux kernel, published on 15 Jan 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
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: CWE-667
Which versions are affected by CVE-2024-57889?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2024-57889?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2024-57889 being exploited?
There is no known exploitation of CVE-2024-57889 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2024-57889, DEBIAN-CVE-2024-57889, GHSA-5xqg-j6jp-j9g5, UBUNTU-CVE-2024-57889.