bugprone-not-null-terminated-result¶
Finds function calls where it is possible to cause a not null-terminated result.
Usually the proper length of a string is strlen(src) + 1
or equal length of
this expression, because the null terminator needs an extra space. Without the
null terminator it can result in undefined behavior when the string is read.
The following and their respective wchar_t
based functions are checked:
memcpy
, memcpy_s
, memchr
, memmove
, memmove_s
,
strerror_s
, strncmp
, strxfrm
The following is a real-world example where the programmer forgot to increase
the passed third argument, which is size_t length
. That is why the length
of the allocated memory is not enough to hold the null terminator.
static char *stringCpy(const std::string &str) {
char *result = reinterpret_cast<char *>(malloc(str.size()));
memcpy(result, str.data(), str.size());
return result;
}
In addition to issuing warnings, fix-it rewrites all the necessary code. It also tries to adjust the capacity of the destination array:
static char *stringCpy(const std::string &str) {
char *result = reinterpret_cast<char *>(malloc(str.size() + 1));
strcpy(result, str.data());
return result;
}
Note: It cannot guarantee to rewrite every of the path-sensitive memory allocations.
Transformation rules of ‘memcpy()’¶
It is possible to rewrite the memcpy()
and memcpy_s()
calls as the
following four functions: strcpy()
, strncpy()
, strcpy_s()
,
strncpy_s()
, where the latter two are the safer versions of the former two.
It rewrites the wchar_t
based memory handler functions respectively.
Rewrite based on the destination array¶
If copy to the destination array cannot overflow [1] the new function should be the older copy function (ending with
cpy
), because it is more efficient than the safe version.If copy to the destination array can overflow [1] and
WantToUseSafeFunctions
is set to true and it is possible to obtain the capacity of the destination array then the new function could be the safe version (ending withcpy_s
).If the new function is could be safe version and C++ files are analyzed and the destination array is plain
char
/wchar_t
withoutun/signed
then the length of the destination array can be omitted.If the new function is could be safe version and the destination array is
un/signed
it needs to be casted to plainchar *
/wchar_t *
.
- [1] It is possible to overflow:
If the capacity of the destination array is unknown.
If the given length is equal to the destination array’s capacity.
Rewrite based on the length of the source string¶
If the given length is
strlen(source)
or equal length of this expression then the new function should be the older copy function (ending withcpy
), as it is more efficient than the safe version (ending withcpy_s
).Otherwise we assume that the programmer wanted to copy ‘N’ characters, so the new function is
ncpy
-like which copies ‘N’ characters.
Transformations with ‘strlen()’ or equal length of this expression¶
It transforms the wchar_t
based memory and string handler functions
respectively (where only strerror_s
does not have wchar_t
based alias).
Memory handler functions¶
memcpy
Please visit the
Transformation rules of ‘memcpy()’ section.
memchr
Usually there is a C-style cast and it is needed to be removed, because the
new function strchr
’s return type is correct. The given length is going
to be removed.
memmove
If safe functions are available the new function is memmove_s
, which has
a new second argument which is the length of the destination array, it is
adjusted, and the length of the source string is incremented by one.
If safe functions are not available the given length is incremented by one.
memmove_s
The given length is incremented by one.
String handler functions¶
strerror_s
The given length is incremented by one.
strncmp
If the third argument is the first or the second argument’s length + 1
it has to be truncated without the + 1
operation.
strxfrm
The given length is incremented by one.
Options¶
- WantToUseSafeFunctions¶
The value true specifies that the target environment is considered to implement ‘_s’ suffixed memory and string handler functions which are safer than older versions (e.g. ‘memcpy_s()’). The default value is true.