Use After Free in vim/vim

An attacker can trigger this use-after-free by crafting a Vim script file (or persuading a user to open one) that defines a function with line continuations, causing `get_function_line()` to allocate and free lines in an unsafe manner. The old code used a single `line_to_free` pointer to track the last allocated line; when multiple lines were fetched, a previously freed line could still be referenced via `eap->cmdlinep`, leading to a use-after-free when that pointer is later dereferenced [ref_id=1]. No authentication or special privileges are required beyond opening the malicious file in Vim.

The vulnerability affects Vim's function definition parsing code, specifically `get_function_line()`, `get_function_args()`, `get_function_body()`, `define_function()`, and `ex_function()` in the Vim source tree. The patch modifies these functions to replace a single `line_to_free` pointer with a `garray_T lines_to_free` array, fixing a use-after-free condition that occurs when multiple lines are allocated during function parsing.

The patch replaces the single `char_u *line_to_free` pointer with a `garray_T lines_to_free` growable array that tracks all allocated lines [ref_id=1]. Instead of freeing the old line and replacing the pointer on each new line fetch, the new code appends each line to `lines_to_free` via `ga_add_string()` and only frees the entire array at cleanup with `ga_clear_strings()`. This ensures no dangling pointer remains in `eap->cmdlinep` after a line is freed, closing the use-after-free window.