Fix invalid memory references - #3814
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When we receive a packet of exactly four bytes encoding its length as those four bytes it can be treated as an empty line. While it is not really specified how those empty lines should be treated, we currently ignore them and do not return an error when trying to parse it but simply advance the data pointer. Callers invoking `git_pkt_parse_line` are currently not prepared to handle this case as they do not explicitly check this case. While they could always reset the passed out-pointer to `NULL` before calling `git_pkt_parse_line` and determine if the pointer has been set afterwards, it makes more sense to update `git_pkt_parse_line` to set the out-pointer to `NULL` itself when it encounters such an empty packet. Like this it is guaranteed that there will be no invalid memory references to free'd pointers. As such, the issue has been fixed such that `git_pkt_parse_line` always sets the packet out pointer to `NULL` when an empty packet has been received and callers check for this condition, skipping such packets.
When removing an entry from the index by its position, we first retrieve the position from the index's entries and then try to remove the retrieved value from the index map with `DELETE_IN_MAP`. When `index_remove_entry` returns `NULL` we try to feed it into the `DELETE_IN_MAP` macro, which will unconditionally call `idxentry_hash` and then happily dereference the `NULL` entry pointer. Fix the issue by not passing a `NULL` entry into `DELETE_IN_MAP`.
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This looks good to me. In reference to one of your comments:
Indeed this is the expectation - although this is not codified in a document, the expectation is that functions that take out-params should always set those, even in error cases. 👍 |
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Two small fixes for invalid memory references. As always, some details are included in the commit messages.
I've pushed a fix similar to the smart-transports commit once before, but back then the fix wasn't as obvious and as I wasn't able to recap my own thought process when you asked about the non-obvious fix I simply dropped the commit. But I hope the issue should be clear now.