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In the Linux kernel, the following vulnerability has been resolved: ACPI: battery: Fix possible crash when unregistering a battery hook When a battery hook returns an error when adding a new battery, then the battery hook is automatically unregistered. However the battery hook provider cannot know that, so it will later call battery_hook_unregister() on the already unregistered battery hook, resulting in a crash. Fix this by using the list head to mark already unregistered battery hooks as already being unregistered so that they can be ignored by battery_hook_unregister().
CVSS 3.1 Base Score 5.5. CVSS Attack Vector: local. CVSS Attack Complexity: low. CVSS Vector: (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H).
The following code shows a simple example of a use after free error:
}free(ptr);logError("operation aborted before commit", ptr);When an error occurs, the pointer is immediately freed. However, this pointer is later incorrectly used in the logError function.
In the following C/C++ example the method processMessage is used to process a message received in the input array of char arrays. The input message array contains two char arrays: the first is the length of the message and the second is the body of the message. The length of the message is retrieved and used to allocate enough memory for a local char array, messageBody, to be created for the message body. The messageBody is processed in the method processMessageBody that will return an error if an error occurs while processing. If an error occurs then the return result variable is set to indicate an error and the messageBody char array memory is released using the method free and an error message is sent to the logError method.
}
return result;
}free(messageBody);result = FAIL;logError("Error processing message", messageBody);However, the call to the method logError includes the messageBody after the memory for messageBody has been released using the free method. This can cause unexpected results and may lead to system crashes. A variable should never be used after its memory resources have been released.
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