c.lang.correctness.incorrect-use-sscanf-fn.incorrect-use-sscanf-fn

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LGPL Commons Clause
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Avoid 'sscanf()' for number conversions. Its use can lead to undefined behavior, slow processing, and integer overflows. Instead prefer the 'strto*()' family of functions.

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Defintion

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rules:
  - id: incorrect-use-sscanf-fn
    patterns:
      - pattern: sscanf($STR, $FMT, $PTR);
      - metavariable-regex:
          metavariable: $FMT
          regex: '"%(l{0,2}|L)([fegEa]|[dDiouxX])"'
    message: Avoid 'sscanf()' for number conversions. Its use can lead to undefined
      behavior, slow processing, and integer overflows. Instead prefer the
      'strto*()' family of functions.
    metadata:
      references:
        - https://stackoverflow.com/q/22865622
        - https://stackoverflow.com/q/7021725
        - https://www.mattkeeter.com/blog/2021-03-01-happen/
      category: correctness
      technology:
        - c
      license: Commons Clause License Condition v1.0[LGPL-2.1-only]
    languages:
      - c
    severity: WARNING

Examples

incorrect-use-sscanf-fn.c

#include <stdio.h>
#include <stdlib.h>

int main() {
    const char *float_str = "3.1415926535897932384626433832";
    const char *int_str = "9999999999999999999999999";
    int read;

    float f;
    double d;
    long double ld;

    // ruleid:incorrect-use-sscanf-fn
    read = sscanf(float_str, "%f", &f);

    // ruleid:incorrect-use-sscanf-fn
    read = sscanf(float_str, "%lf", &d);

    // ruleid:incorrect-use-sscanf-fn
    read = sscanf(float_str, "%llf", &ld);

    // ruleid:incorrect-use-sscanf-fn
    read = sscanf(float_str, "%Lf", &ld);

    // ok:incorrect-use-sscanf-fn
    f = strtof(float_str, NULL);

    // ok:incorrect-use-sscanf-fn
    d = strtod(float_str, NULL);

    // ok:incorrect-use-sscanf-fn
    ld = strtold(float_str, NULL);

    int i;
    long int li;
    long long int lli;
    unsigned int ui;
    unsigned long int uli;
    unsigned long long int ulli;

    // ruleid:incorrect-use-sscanf-fn
    read = sscanf(int_str, "%d", &i);

    // ruleid:incorrect-use-sscanf-fn
    read = sscanf(int_str, "%ld", &li);

    // ruleid:incorrect-use-sscanf-fn
    read = sscanf(int_str, "%lld", &lli);

    // ruleid:incorrect-use-sscanf-fn
    read = sscanf(int_str, "%Ld", &lli);

    // ruleid:incorrect-use-sscanf-fn
    read = sscanf(int_str, "%u", &ui);

    // ruleid:incorrect-use-sscanf-fn
    read = sscanf(int_str, "%lu", &uli);

    // ruleid:incorrect-use-sscanf-fn
    read = sscanf(int_str, "%llu", &ulli);

    // ruleid:incorrect-use-sscanf-fn
    read = sscanf(int_str, "%Lu", &ulli);

    // ok:incorrect-use-sscanf-fn
    li = strtol(int_str, NULL, 0);

    // ok:incorrect-use-sscanf-fn
    lli = strtoll(int_str, NULL, 0);

    // ok:incorrect-use-sscanf-fn
    uli = strtoul(int_str, NULL, 0);

    // ok:incorrect-use-sscanf-fn
    ulli = strtoull(int_str, NULL, 0);

    return 0;
}