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Date: Wed, 17 Apr 2024 23:06:36 +0000
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Message-ID: <20240417230637.2592473-1-dtokazaki@google.com>
Subject: [PATCH v1] at24: fix memory corruption race condition
From: Daniel Okazaki <dtokazaki@google.com>
To: Bartosz Golaszewski <brgl@bgdev.pl>, Arnd Bergmann <arnd@arndb.de>, 
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Daniel Okazaki <dtokazaki@google.com>, kernel-team@android.com, 
	linux-i2c@vger.kernel.org, linux-kernel@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"

If the eeprom is not accessible, an nvmem device will be registered, the
read will fail, and the device will be torn down. If another driver
accesses the nvmem device after the teardown, it will reference
invalid memory.

Move the failure point before registering the nvmem device.

Signed-off-by: Daniel Okazaki <dtokazaki@google.com>
---
 drivers/misc/eeprom/at24.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/drivers/misc/eeprom/at24.c b/drivers/misc/eeprom/at24.c
index 572333ead5fb..4bd4f32bcdab 100644
--- a/drivers/misc/eeprom/at24.c
+++ b/drivers/misc/eeprom/at24.c
@@ -758,15 +758,6 @@ static int at24_probe(struct i2c_client *client)
 	}
 	pm_runtime_enable(dev);
 
-	at24->nvmem = devm_nvmem_register(dev, &nvmem_config);
-	if (IS_ERR(at24->nvmem)) {
-		pm_runtime_disable(dev);
-		if (!pm_runtime_status_suspended(dev))
-			regulator_disable(at24->vcc_reg);
-		return dev_err_probe(dev, PTR_ERR(at24->nvmem),
-				     "failed to register nvmem\n");
-	}
-
 	/*
 	 * Perform a one-byte test read to verify that the chip is functional,
 	 * unless powering on the device is to be avoided during probe (i.e.
@@ -782,6 +773,15 @@ static int at24_probe(struct i2c_client *client)
 		}
 	}
 
+	at24->nvmem = devm_nvmem_register(dev, &nvmem_config);
+	if (IS_ERR(at24->nvmem)) {
+		pm_runtime_disable(dev);
+		if (!pm_runtime_status_suspended(dev))
+			regulator_disable(at24->vcc_reg);
+		return dev_err_probe(dev, PTR_ERR(at24->nvmem),
+				     "failed to register nvmem\n");
+	}
+
 	/* If this a SPD EEPROM, probe for DDR3 thermal sensor */
 	if (cdata == &at24_data_spd)
 		at24_probe_temp_sensor(client);
-- 
2.44.0.683.g7961c838ac-goog