Call to a thread-unsafe (non-reentrant) libc function

ID

c.correctness.mt_unsafe

Severity

low

Remediation Complexity

medium

Remediation Risk

medium

Remediation Effort

medium

Resource

Concurrency

Language

C / C++

Description

Call to a non-reentrant / thread-unsafe libc function. These functions use shared internal state (static buffers or global state) and misbehave when called concurrently from multiple threads. Prefer the reentrant _r variant (e.g. localtime_r, gmtime_r, strtok_r, rand_r) or a thread-safe alternative, and guard shared state where no reentrant variant exists.

Rationale

Call to a non-reentrant / thread-unsafe libc function. These functions use shared internal state (static buffers or global state) and misbehave when called concurrently from multiple threads. Prefer the reentrant _r variant (e.g. localtime_r, gmtime_r, strtok_r, rand_r) or a thread-safe alternative, and guard shared state where no reentrant variant exists.

The following code illustrates the pattern detected by this rule:

void foo(time_t *t, char *s)
{
    // FLAGGED: Call to a thread-unsafe (non-reentrant) libc function
    gmtime(t);
    // FLAGGED: Call to a thread-unsafe (non-reentrant) libc function
    localtime(t);
    // FLAGGED: Call to a thread-unsafe (non-reentrant) libc function
    asctime(NULL);
    // FLAGGED: Call to a thread-unsafe (non-reentrant) libc function
    ctime(t);
    // FLAGGED: Call to a thread-unsafe (non-reentrant) libc function
    strtok(s, ",");
    // FLAGGED: Call to a thread-unsafe (non-reentrant) libc function
    rand();
    // FLAGGED: Call to a thread-unsafe (non-reentrant) libc function
    srand(1);
    // FLAGGED: Call to a thread-unsafe (non-reentrant) libc function
    getenv("PATH");
    // FLAGGED: Call to a thread-unsafe (non-reentrant) libc function
    tmpnam(NULL);
    // FLAGGED: Call to a thread-unsafe (non-reentrant) libc function
    getpwnam("root");
    // FLAGGED: Call to a thread-unsafe (non-reentrant) libc function
    getlogin();
    // FLAGGED: Call to a thread-unsafe (non-reentrant) libc function
    ttyname(0);
}

Remediation

Follow secure coding practices and review the references below for detailed remediation guidance.

Configuration

This detector does not need any configuration.

References