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This noncompliant code example assumes that the size of {{struct buffer}} is equal to the sum of the size of its individual components, which may not be the case \[[Dowd 2006|AA. Bibliography#Dowd 06]\]. The size of {{struct buffer}} may actually be larger due to structure padding. |
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enum { buffer_size = 50 };
struct buffer {
size_t size;
char bufferC[buffer_size];
} buff;
/* ... */
void func(const struct buffer *buf) {
/*
* Incorrectly assumes sizeof(struct buffer) =
* sizeof(size_t) + sizeof(buff.bufferC)
*/
struct buffer *buf_cpy = (struct buffer *)malloc(
sizeof(size_t) + sizeof(buff.bufferC)
);
if (buf_cpy == NULL) {
/* Handle malloc() error */
}
/*
* With padding, sizeof(struct buffer) may be greater than
* sizeof(size_t) + sizeof(buff.bufferC), causing some data
* to be written outside the bounds of the memory allocated.
*/
memcpy(buf_cpy, buf, sizeof(struct buffer));
/* ... */
free(buf_cpy);
}
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Accounting for structure padding prevents these types of errors.
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enum { buffer_size = 50 };
struct buffer {
size_t size;
char bufferC[buffer_size];
} buff;
/* ... */
void func(const struct buffer *buf) {
struct buffer *buf_cpy =
(struct buffer *)malloc(sizeof(struct buffer));
if (buf_cpy == NULL) {
/* Handle malloc() error */
}
/* ... */
memcpy(buf_cpy, buf, sizeof(struct buffer));
/* ... */
free(buf_cpy);
}
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