CFSTORE Bugfix for realloc() moving KV area and cfstore_file_t data structures not being updated correctly

[simonqhughes]

This commit contains CFSTORE fixes for the following related issues:

• issue 17: Heap corruption (https://github.com/ARMmbed/configuration-store/issues/17)
• issue 23: Handles invalidated when realloc called (https://github.com/ARMmbed/configuration-store/issues/23)
• issue 24: cfstore_find returns error when "previous" parameter is NULL (https://github.com/ARMmbed/configuration-store/issues/24)
• issue 25: Memory leak when out of memory (https://github.com/ARMmbed/configuration-store/issues/25)

With respect to issues 17 and 23:

• A code defect existed for correctly updating cfstore_file_t data structures under the following conditions:
  -- the KV memory area contained some KV's.
  -- cfstore calls realloc() to increase the size of the KV area in memory because:
  * A new KV was being added to the KV area, or
  * The size of a pre-existing KV was being increased.
  -- The returned address from realloc() has changed from before the call (i.e. the location in memory of the KV area has changed) e.g. the presence of heap memory objects directly above the KV memory area in the memory address space causes realloc() to move the KV area so the newly increased area can be accommodated at contiguous addresses.
  -- In this scenario, the cfstore_file_t (structures for open files) head pointers do not get correctly updated.
  -- The defect was fixed by correctly updating the cfstore_file_t:: head pointer.
  -- A new add_del test case was added to the scenario where a new KV is being added to the KV area.
  -- A new create test case was added to the scenario where the size of a pre-existing KV is being increased in size.
• A code defect for supplying a NULL handle as the previous argument to the Find() method (issue 24).
  -- Supply a null handle is valid, but it was being used to check for a valid hkey, which was incorrect.
  -- A new test case was added to check the case of supplying a NULL previous argument works correctly.
• A code defect for a memory leak under the following conditions (issue 25):
  -- When realloc() fails to perform a requested change to the size of the KV area, the error handling sometimes incorrectly sets cfstore_context_t::area_0_head to NULL.
  -- Cfstore returns a suitable error to the client. If memory had previously been held at area_0_head, realloc(area_0_head, size) returning NULL means the memory at area_0_head is still retained.
  -- On receiving the error code, the client cleans up including a call to Uninitialize(). This should free the retained but as area_0_head == NULL this is not possible. Hence a memory leak occurred.
  -- This was fixed by not setting area_0_head = NULL on the realloc() failure.
  -- A create test case was modified to detect the leaking of memory in this way.

Notifications to interested parties:
@c1728p9 @jenia81 @mottigondabi

[c1728p9]

possible typo - did you mean to write an rather than and?

[simonqhughes]

Its a typo. Thanks. I'll fix in a subsequent commit if that's OK.

[c1728p9]

I skimmed over the patch and it looks good to me. Thanks for the fixes and tests to catch future regressions.

[sg-]

/morph test

[mbed-bot]

Result: SUCCESS

Your command has finished executing! Here's what you wrote!

/morph test

Output

mbed Build Number: 816

All builds and test passed!