[PATCH v2] i2c: i801: fix hardware state machine corruption in error path

[<w15303746062@163.com>]

From: Mingyu Wang <25181214217@stu.xidian.edu.cn>

A severe livelock and subsequent Hung Task panic were observed in the
i2c-i801 driver during concurrent Fuzzing. The crash is caused by an
unconditional hardware register cleanup in the error handling path of
i801_access().

When i801_check_pre() fails (e.g., returning -EBUSY because the SMBus
controller is actively used by BIOS/ACPI), the kernel does not actually
acquire the hardware ownership. However, the code jumps to the 'out'
label and executes:

    iowrite8(SMBHSTSTS_INUSE_STS | STATUS_FLAGS, SMBHSTSTS(priv));

This forcefully clears the INUSE_STS lock and resets the hardware status
flags without owning the controller. Doing so interrupts ongoing BIOS/ACPI
transactions and totally corrupts the SMBus hardware state machine.

Consequently, all subsequent i801_access() calls fail at the pre-check
stage, triggering an endless stream of "SMBus is busy, can't use it!"
error logs. Over a slow serial console, this printk flood monopolizes
the CPU (Console Livelock), starving other processes trying to acquire
the mmap_lock down_read semaphore, ultimately triggering the hung task
watchdog.

Fix this by moving the 'out' label below the hardware register cleanup.
If i801_check_pre() fails, we safely bypass the iowrite8() and only
release the software locks (pm_runtime and mutex), strictly adhering to
the rule of not releasing resources that were never acquired.

Fixes: 1f760b87e54c ("i2c: i801: Call i801_check_pre() from i801_access()")
Cc: stable@vger.kernel.org # v6.3+

Signed-off-by: Mingyu Wang <25181214217@stu.xidian.edu.cn>
---
Changes in v2:
 - Reused and moved the existing 'out' label instead of adding a new one,
   fixing a build warning regarding an unused label.
 - Dropped the inaccurate mention of "another thread" in the commit message,
   as i801_access() is serialized by a mutex.
 - Added Fixes and Cc stable tags as suggested.

 drivers/i2c/busses/i2c-i801.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/i2c/busses/i2c-i801.c b/drivers/i2c/busses/i2c-i801.c
index 32a3cef02c7b..b29c99ed3883 100644
--- a/drivers/i2c/busses/i2c-i801.c
+++ b/drivers/i2c/busses/i2c-i801.c
@@ -931,13 +931,13 @@ static s32 i801_access(struct i2c_adapter *adap, u16 addr,
 	 */
 	if (hwpec)
 		iowrite8(ioread8(SMBAUXCTL(priv)) & ~SMBAUXCTL_CRC, SMBAUXCTL(priv));
-out:
 	/*
 	 * Unlock the SMBus device for use by BIOS/ACPI,
 	 * and clear status flags if not done already.
 	 */
 	iowrite8(SMBHSTSTS_INUSE_STS | STATUS_FLAGS, SMBHSTSTS(priv));
 
+out:
 	pm_runtime_put_autosuspend(&priv->pci_dev->dev);
 	mutex_unlock(&priv->acpi_lock);
 	return ret;
-- 
2.34.1