libsubid: Memory Management in Different Heap States
daskol opened this issue · 5 comments
As in release shadow 4.15.1, libsubid assumes that the same allocator (presumably glibc) is used across caller and callee code. The issue is getting worse in a situation when libsubid forward subordinate management to a plugin according to nsswitch.conf. In this case, memory management gets more complicated: one must be sure that a plugin and a caller use the same allocator which shares the same heap state. The issue is that a caller can use glibc malloc while a plugin uses jemalloc/tcmalloc/etc or none of them at all if a plugin is not written in C/C++.
I propose two ways to tackle the issue. In the first solution, libsubid public API should be extended with subid_free routine to release memory allocated in a plugin. The advantage of this solution is its simplicity and it requires only small changes (writing new code, mostly).
struct subid_range *ranges;
int count = subid_get_uid_ranges("username", &ranges);
// do something with ranges.
subid_free(ranges);The second approach is wide-spread as well. It requires API call to estimate buffer size first and allocating a buffer on a caller side.
int count = subid_get_uid_ranges_count("username");
if (count < 0) {
throw std::runtime_exception(...);
}
auto ranges = std::make_unique<subid_range[]>(count);
subid_get_uid_ranges("username", ranges.get());
// do something with ranges.What do you think?
@hallyn @alejandro-colomar Any comments?
I propose two ways to tackle the issue. In the first solution, libsubid public API should be extended with subid_free routine to release memory allocated in a plugin. The advantage of this solution is its simplicity and it requires only small changes (writing new code, mostly).
struct subid_range *ranges; int count = subid_get_uid_ranges("username", &ranges); // do something with ranges. subid_free(ranges);The second approach is wide-spread as well. It requires API call to estimate buffer size first and allocating a buffer on a caller side.
int count = subid_get_uid_ranges_count("username"); if (count < 0) { throw std::runtime_exception(...); } auto ranges = std::make_unique<subid_range[]>(count); subid_get_uid_ranges("username", ranges.get()); // do something with ranges.What do you think?
Both sound good to me.
Great. I will prepare pull request then.
I prefer the first.
I guess we can close this. If you need anything else, feel free to reopen.