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In the Linux kernel, the following vulnerability has been resolved: drm/xe/guc_submit: add missing locking in wedged_fini Any non-wedged queue can have a zero refcount here and can be running concurrently with an async queue destroy, therefore dereferencing the queue ptr to check wedge status after the lookup can trigger UAF if queue is not wedged. Fix this by keeping the submission_state lock held around the check to postpone the free and make the check safe, before dropping again around the put() to avoid the deadlock. (cherry picked from commit d28af0b6b9580b9f90c265a7da0315b0ad20bbfd)
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).
In the following Java snippet, methods are defined to get and set a long field in an instance of a class that is shared across multiple threads. Because operations on double and long are nonatomic in Java, concurrent access may cause unexpected behavior. Thus, all operations on long and double fields should be synchronized.
}return someLongValue;someLongValue = l;This code tries to obtain a lock for a file, then writes to it.
fclose($logFile);}//attempt to get logfile lockflock($logfile, LOCK_UN);// unlock logfileprint "Could not obtain lock on logFile.log, message not recorded\n";PHP by default will wait indefinitely until a file lock is released. If an attacker is able to obtain the file lock, this code will pause execution, possibly leading to denial of service for other users. Note that in this case, if an attacker can perform an flock() on the file, they may already have privileges to destroy the log file. However, this still impacts the execution of other programs that depend on flock().
The following function attempts to acquire a lock in order to perform operations on a shared resource.
}
pthread_mutex_unlock(mutex);/* access shared resource */However, the code does not check the value returned by pthread_mutex_lock() for errors. If pthread_mutex_lock() cannot acquire the mutex for any reason the function may introduce a race condition into the program and result in undefined behavior.
In order to avoid data races correctly written programs must check the result of thread synchronization functions and appropriately handle all errors, either by attempting to recover from them or reporting it to higher levels.
}
return pthread_mutex_unlock(mutex);return result;/* access shared resource */It may seem that the following bit of code achieves thread safety while avoiding unnecessary synchronization...
return helper;
}}helper = new Helper();The programmer wants to guarantee that only one Helper() object is ever allocated, but does not want to pay the cost of synchronization every time this code is called.
Suppose that helper is not initialized. Then, thread A sees that helper==null and enters the synchronized block and begins to execute:
helper = new Helper();If a second thread, thread B, takes over in the middle of this call and helper has not finished running the constructor, then thread B may make calls on helper while its fields hold incorrect values.
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