remote: fix memory leak in git_remote_download()

[7Ji]

connect_opts is created with its custom_headers and proxy_opts->url possibly allocated on heap, just like in git_remote_fetch(). But unlike in _fetch(), it is not disposed at the end of the function, thus causing memory leak.

---

A backtrace demostrating the issue (from the demo below):

=================================================================
==24905==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 22 byte(s) in 1 object(s) allocated from:
    #0 0x7f4cb4ce1359 in __interceptor_malloc /usr/src/debug/gcc/gcc/libsanitizer/asan/asan_malloc_linux.cpp:69
    #1 0x7f4cb52e942e in stdalloc__malloc /tmp/libgit2/src/util/allocators/stdalloc.c:20
    #2 0x7f4cb52e9040 in git__malloc /tmp/libgit2/src/util/alloc.h:19
    #3 0x7f4cb52e9229 in git__strdup /tmp/libgit2/src/util/alloc.c:54
    #4 0x7f4cb53a4605 in git_proxy_options_dup /tmp/libgit2/src/libgit2/proxy.c:35
    #5 0x7f4cb53ba916 in git_remote_connect_options_dup /tmp/libgit2/src/libgit2/remote.c:777
    #6 0x7f4cb53badc8 in git_remote_connect_options_normalize /tmp/libgit2/src/libgit2/remote.c:917
    #7 0x7f4cb53b8426 in git_remote_connect_options__from_fetch_opts /tmp/libgit2/src/libgit2/remote.h:79
    #8 0x7f4cb53bc038 in git_remote_download /tmp/libgit2/src/libgit2/remote.c:1335
    #9 0x55a04d5bc99d in main (/tmp/demo+0x199d) (BuildId: 44836a470bc5c2b8ad0414dcda4639c66e0af9f2)
    #10 0x7f4cb4a45ccf  (/usr/lib/libc.so.6+0x27ccf) (BuildId: 8bfe03f6bf9b6a6e2591babd0bbc266837d8f658)

SUMMARY: AddressSanitizer: 22 byte(s) leaked in 1 allocation(s).

The demo:

#include <stdio.h>
#include <stdlib.h>
#include <git2.h>

int main() {
    git_repository *repo;
    git_remote *remote;
    git_remote_callbacks callbacks = GIT_REMOTE_CALLBACKS_INIT;
    git_fetch_options fetch_opts = GIT_FETCH_OPTIONS_INIT;
    char const *refspecs_strings[] = {"+refs/*:refs/*", NULL};
    git_strarray const refspecs = { .count = 1, .strings = (char **)refspecs_strings };
    int r;

    fetch_opts.proxy_opts.url = "http://xray.lan:11092";
    fetch_opts.proxy_opts.type = GIT_PROXY_SPECIFIED;

    git_libgit2_init();
    
    if (git_repository_open_bare(&repo, "/tmp/demo.git")) {
        printf("Failed to open repo\n");
        return -1;
    }
    if (git_remote_create_anonymous(&remote, repo, "https://github.com/7Ji/buildos.git")) {
        printf("Failed to create remote\n");
        r = -1;
        goto free_repo;
    }
#ifdef DEMO_MANUAL_DOWNLOAD
    if (git_remote_connect(remote, GIT_DIRECTION_FETCH, &callbacks, &fetch_opts.proxy_opts, NULL)) {
        printf("Failed to connect\n");
        r = -1;
        goto free_remote;
    }
    if (git_remote_download(remote, &refspecs, &fetch_opts)) {
        printf("Failed to download\n");
        r = -1;
        goto free_remote;
    }
    if (git_remote_disconnect(remote)) {
        printf("Failed to disconnect\n");
        r = -1;
        goto free_remote;
    }
#else
    if (git_remote_fetch(remote, &refspecs, &fetch_opts, NULL)) {
        printf("Failed to fetch\n");
        r = -1;
        goto free_remote;
    }
#endif
    r = 0;
free_remote:
    git_remote_free(remote);
free_repo:
    git_repository_free(repo);
    git_libgit2_shutdown();
    return r;
}

Compile with (where /tmp/libgit2_debug stores a libgit2 build with address sanitizer enabled)

gcc demo.c -fsanitize=address -L/tmp/libgit2_debug -lgit2 -DDEMO_MANUAL_DOWNLOAD=yes -o demo_download
gcc demo.c -fsanitize=address -L/tmp/libgit2_debug -lgit2 -o demo_fetch

Run with

LD_LIBRARY_PATH=/tmp/libgit2_debug ./demo_fetch
LD_LIBRARY_PATH=/tmp/libgit2_debug ./demo_download

[ethomson]

Thanks! Good catch. 😁