UnsafeImplicitConversions.md

Unsafe Implicit Conversions

Integer variables may be implicitly casted to a type of different size and signedness. If the variable is casted to a type of smaller bit-size or different signedness without a proper bound checking, then the casting may silently truncate the variable's value or make it semantically meaningless. This query finds implicit casts that cannot be proven to be safe.

Recommendation

Either change variables types to avoid implicit conversions or verify that converting highlighted variables is always safe.

Example

/*
 * Compile: clang++ -Wall -pedantic UnsafeImplicitConversions.cpp
 * Test: ./a.out 0x100000001
*/
#include <stdlib.h>
#include <string.h>

char* malloc_wrapper(int size) {
    return (char*)malloc(size);
}

void test(uint64_t large) {
    char *p = malloc_wrapper(large);
    memset(p, 0, large);
    free(p);
}

int main(int argc, char *argv[]) {
    if (argc < 2)
        return 1;

    test(strtol(argv[1], NULL, 16));
    return 0;
}

In this example, the call to malloc_wrapper may silently truncate large variable, and so the allocated buffer will be of smaller size than the test function expects.