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C

C static code analysis

Unique rules to find Bugs, Vulnerabilities, Security Hotspots, and Code Smells in your C code

  • All rules 315
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  • Quick Fix 19
Filtered: 6 rules found
multi-threading
    Impact
      Clean code attribute
        1. "pthread_mutex_t" should be unlocked in the reverse order they were locked

           Bug
        2. "pthread_mutex_t" should be properly initialized and destroyed

           Bug
        3. "pthread_mutex_t" should not be locked when already locked, or unlocked when already unlocked

           Bug
        4. Blocking functions should not be called inside critical sections

           Code Smell
        5. Local variables and member data should not be volatile

           Code Smell
        6. Non-reentrant POSIX functions should be replaced with their reentrant versions

           Code Smell

        "pthread_mutex_t" should not be locked when already locked, or unlocked when already unlocked

        intentionality - logical
        reliability
        Bug
        • cwe
        • symbolic-execution
        • multi-threading

        pthread_mutex_t should not be locked when already locked, or unlocked when already unlocked.

        Why is this an issue?

        How can I fix it?

        More Info

        Mutexes are synchronization primitives that allow to manage concurrency. This is the most fundamental building block for creating safe concurrent applications. By using a mutex, one can ensure that a block of code is executed by a single thread concurrently. Data structures are designed to maintain their invariants between member-function calls. If a data structure is accessed concurrently, and one of the accesses is a write operation, then it has a data race. Having data races is undefined behavior.

        Adversaries actively exploit data races to take over systems, but data races are also a common source of data corruption in concurrent applications resulting in dormant and hard-to-find bugs.

        To prevent data races, the shared resource (usually memory) must be protected by obtaining mutual access to the data during both reading and writing. Such mutual exclusion is generally achieved by using a mutex, which is frequently referred to as a lock.

        A mutex has two states: released - which is the initial state, or acquired. These two states are frequently called unlocked and locked as well.

        To effectively protect the shared resource from concurrent accesses, all such accesses should be guarded by the same mutex. They need to lock the mutex to gain safe exclusive access to the resource and unlock it after they are done mutating or reading it.

        You can abstract away the concurrent threads sharing the mutex and think of it as owned by the current thread. It never spontaneously changes between acquired and released.

        In this view, these are the possible transitions when calling lock or unlock on a mutex in a given state:

        1. released + lock() ⇒ acquired
        2. acquired + unlock() ⇒ released
        3. acquired + lock() ⇒ deadlock
        4. released + unlock() ⇒ undefined behavior

        When a thread locks a mutex, another thread trying to acquire the same mutex will be blocked and have to wait for the first thread to release it. This waiting period can take some time. If a thread attempts to lock a mutex it has already acquired, it will deadlock because it would need to release it to lock it again.

        What is the potential impact?

        Locking an acquired mutex leads to a deadlock, as a mutex can only be obtained once. Unlocking a released mutex is undefined behavior. Removing synchronization can cause data races, leading to data corruption, which adversaries might leverage to take over the system.

        Exceptions

        There are recursive mutexes that can be acquired multiple times by the same thread, given that just as many times we also release the mutex. They are rare in practice and usually signal design problems in the code. Thus we assume pthread_mutex_t refers to non-recursive mutexes.

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