hope your having a nice day; so i have the following code that i want to know if it would somehow overflow at some point ::
static void * myalloc(size_t len) {
void * p = malloc(len);
if (p == NULL) {
fprintf(stderr, "end of memory\n");
exit(1);
}
return p;
}
static void * copy_buf(void * buf, uint32_t count, uint32_t be) {
uint32_t * p = NULL;
if (buf != NULL) {
p = myalloc(count * 4);
memcpy(p, buf, count * 4);
}
// more code
return p;
}
if it did not overflow, would something else cause it to do so, i mean if the variables changed. or the parameters changed (not the data type of course, but the value of them).
thank you for your help, the full source code is much bigger (more than a one file and more that 2000 lines of code for each one), but this is one of the parts that i am concerned about…
count * 4 might overflow if count was less than SIZE_MAX / 4 (SIZE_MAX is the maximum value a size_t can hold), since memcpy take a size_t as the third argument, but I’m not sure if that would cause any problem
In your code, there is a possibility of an overflow if the value of count' times 4 is greater than the maximum value that size_t’ can hold. This can lead to a memory overflow, resulting in an incorrect value being given to the `malloc’ function, which may cause unexpected behavior.
solution :
To avoid this problem, you can use a condition to check if count * 4 is greater than a certain value (usually the maximum value of size_t). If it is more, you can print an error message and prevent malloc from running.
Also, if count or be are changed, you must ensure that these changes are within the valid ranges supported by their data type. If count is changed to a very large value whose value times 4 is greater than the maximum value of uint32_t, an overflow may still occur.
Finally, it’s always good to do extra checks to make sure inputs are within safe limits, especially in code that deals with memory. This can include checks to ensure that count and be are logical values before performing memory operations.
llocation Size Mismatch: The function copy_buf allocates memory for the destination buffer using myalloc(count * 4). The size of the allocation is calculated as count * 4 bytes. However, the buffer size calculation does not consider the size of the individual elements in the buffer. Since count is of type uint32_t, which typically represents 32-bit unsigned integers (4 bytes each), the correct calculation for the buffer size in bytes should be count * sizeof(uint32_t).
memcpy Operation: After allocating memory for the destination buffer, the function attempts to copy data from the source buffer (buf) to the destination buffer using memcpy(p, buf, count * 4). Here, count * 4 is used as the size argument to memcpy. If count is a large value, the multiplication might result in an integer overflow, leading to incorrect buffer size calculation and potentially allocating insufficient memory for the destination buffer.
These issues can lead to buffer overflow vulnerabilities of various types:
Integer Overflow: If count is a large value, the multiplication count * 4 might overflow, leading to a smaller-than-expected buffer allocation. Subsequent writes beyond the allocated buffer size due to this miscalculation can cause memory corruption and potentially lead to arbitrary code execution or program crashes.
Buffer Overread: If the source buffer (buf) is larger than the allocated destination buffer, the memcpy operation can read data beyond the bounds of the destination buffer. This can lead to information disclosure or sensitive data exposure.
Buffer Overwrite: Conversely, if the source buffer is smaller than the allocated destination buffer, the memcpy operation might write data beyond the end of the source buffer, potentially overwriting adjacent memory regions. This can lead to memory corruption and unpredictable behavior.