Additional refactoring of ns_turn_allocation.* to address security scanner concerns

[jonesmz]

You can see the list here: https://github.com/coturn/coturn/security/code-scanning

In this case, i'm attempting to address:

ns_turn_allocation.c:725 -- Dereferencing NULL pointer. 'ub->bufs' contains the same NULL value as 'realloc()' did.
ns_turn_allocation.c:724 -- 'realloc' might return null pointer: assigning null pointer to 'ub->bufs', which is passed as an argument to 'realloc', will cause the original memory block to be leaked.
ns_turn_allocation.c:604 -- Dereferencing NULL pointer. 'a->tcs.elems' contains the same NULL value as 'realloc()' did.
ns_turn_allocation.c:582 -- Dereferencing NULL pointer 'tc'.
ns_turn_allocation.c:603 -- 'realloc' might return null pointer: assigning null pointer to 'a->tcs.elems', which is passed as an argument to 'realloc', will cause the original memory block to be leaked.
ns_turn_allocation.c:525 -- Using uninitialized memory '*chi'.
ns_turn_allocation.c:229 -- Using uninitialized memory '*slot'.

[jonesmz]

I'm honestly not sure why the scanner is convinced there's a bug here...

[jonesmz]

@eakraly Anything needed before merging this?

[eakraly]

@jonesmz what were the scanner issues? Could you please mention them in the description? Thanks!

[jonesmz]

You can see the list here: https://github.com/coturn/coturn/security/code-scanning

In this case, i'm attempting to address:

1. ns_turn_allocation.c:725 -- Dereferencing NULL pointer. 'ub->bufs' contains the same NULL value as 'realloc()' did.
2. ns_turn_allocation.c:724 -- 'realloc' might return null pointer: assigning null pointer to 'ub->bufs', which is passed as an argument to 'realloc', will cause the original memory block to be leaked.
3. ns_turn_allocation.c:604 -- Dereferencing NULL pointer. 'a->tcs.elems' contains the same NULL value as 'realloc()' did.
4. ns_turn_allocation.c:582 -- Dereferencing NULL pointer 'tc'.
5. ns_turn_allocation.c:603 -- 'realloc' might return null pointer: assigning null pointer to 'a->tcs.elems', which is passed as an argument to 'realloc', will cause the original memory block to be leaked.
6. ns_turn_allocation.c:525 -- Using uninitialized memory '*chi'.
7. ns_turn_allocation.c:229 -- Using uninitialized memory '*slot'.

[eakraly]

This seems like extra work - the whole parray->extra_slots is released after the loop finishes.

[jonesmz]

certainly, but the analyzer still complains about it.