8000 Cpp: new experimental query cpp/guarded-free by mario-campos · Pull Request #16331 · github/codeql · GitHub
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Merged
merged 4 commits into from
May 1, 2024
Merged

Cpp: new experimental query cpp/guarded-free #16331

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d7c784e
Initial commit of experimental query cpp/guarded-free.
mario-campos Apr 25, 2024
3195f0c
Use more specific `hasGlobalName()` for stdlib function free(3)
mario-campos Apr 26, 2024
c480431
C++: simplify cpp/guarded-free
mario-campos May 1, 2024
5a7a1dc
C++: forgot to import semmle.code.cpp.controlflow.Guards
mario-campos May 1, 2024
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Initial commit of experimental query cpp/guarded-free.
  • Loading branch information
@mario-campos
mario-campos committed Apr 25, 2024
commit d7c784ef2f31bb39cc9418d984bd42c03bb1fb25
11 changes: 11 additions & 0 deletions cpp/ql/src/experimental/Best Practices/GuardedFree.cpp
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void test()
{
char *foo = malloc(100);

// BAD
if (foo)
free(foo);

// GOOD
free(foo);
}
18 changes: 18 additions & 0 deletions cpp/ql/src/experimental/Best Practices/GuardedFree.qhelp
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<!DOCTYPE qhelp SYSTEM "qhelp.dtd">
<qhelp>
<overview>
<p>The <code>free</code> function, which deallocates heap memory, may accept a NULL pointer and take no action. Therefore, it is unnecessary to check its argument for the value of NULL before a function call to <code>free</code>. As such, these guards may hinder performance and readability.</p>
</overview>
<recommendation>
<p>A function call to <code>free</code> should not depend upon the value of its argument. Delete the <code>if</code> condition preceeding a function call to <code>free</code> when its only purpose is to check the value of the pointer to be freed.</p>
</recommendation>
<example>
<sample src = "GuardedFree.cpp" />
</example>
<references>
<li>
The Open Group Base Specifications Issue 7, 2018 Edition:
<a href="https://pubs.opengroup.org/onlinepubs/9699919799/functions/free.html">free - free allocated memory</a>
</li>
</references>
</qhelp>
48 changes: 48 additions & 0 deletions cpp/ql/src/experimental/Best Practices/GuardedFree.ql
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/**
* @name Guarded Free
* @description NULL-condition guards before function calls to the memory-deallocation
* function free(3) are unnecessary, because passing NULL to free(3) is a no-op.
* @kind problem
* @problem.severity recommendation
* @precision very-high
* @id cpp/guarded-free
* @tags maintainability
* readability
* experimental
*/

import cpp

class FreeCall extends FunctionCall {
FreeCall() { this.getTarget().hasName("free") }
}

from IfStmt stmt, FreeCall fc, Variable v
where
stmt.getThen() = fc.getEnclosingStmt() and
(
stmt.getCondition() = v.getAnAccess() and
fc.getArgument(0) = v.getAnAccess()
or
exists(PointerDereferenceExpr cond, PointerDereferenceExpr arg |
fc.getArgument(0) = arg and
stmt.getCondition() = cond and
cond.getOperand+() = v.getAnAccess() and
arg.getOperand+() = v.getAnAccess()
)
or
exists(ArrayExpr cond, ArrayExpr arg |
fc.getArgument(0) = arg and
stmt.getCondition() = cond and
cond.getArrayBase+() = v.getAnAccess() and
arg.getArrayBase+() = v.getAnAccess()
)
or
exists(NEExpr eq |
fc.getArgument(0) = v.getAnAccess() and
stmt.getCondition() = eq and
eq.getAnOperand() = v.getAnAccess() and
eq.getAnOperand().getValue() = "0"
)
)
select stmt, "unnecessary NULL check before call to $@", fc, "free"
0