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builtin/difftool: intialize some hashmap variables

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When running a dir-diff command that produces no diff, variables
`wt_modified` and `tmp_modified` are used while uninitialized, causing:

    $ /home/smarchi/src/git/git-difftool --dir-diff master
    free(): invalid pointer
    [1]    334004 IOT instruction (core dumped)  /home/smarchi/src/git/git-difftool --dir-diff master
    $ valgrind --track-origins=yes /home/smarchi/src/git/git-difftool --dir-diff master
    ...
    Invalid free() / delete / delete[] / realloc()
       at 0x48478EF: free (vg_replace_malloc.c:989)
       by 0x422CAC: hashmap_clear_ (hashmap.c:208)
       by 0x283830: run_dir_diff (difftool.c:667)
       by 0x284103: cmd_difftool (difftool.c:801)
       by 0x238E0F: run_builtin (git.c:484)
       by 0x2392B9: handle_builtin (git.c:750)
       by 0x2399BC: cmd_main (git.c:921)
       by 0x356FEF: main (common-main.c:64)
     Address 0x1ffefff180 is on thread 1's stack
     in frame #2, created by run_dir_diff (difftool.c:358)
    ...

If taking any `goto finish` path before these variables are initialized,
`hashmap_clear_and_free()` operates on uninitialized data, sometimes
causing a crash.

This regression was introduced in 7f795a1715 (builtin/difftool: plug
several trivial memory leaks, 2024-09-26).

Fix it by initializing those variables with the `HASHMAP_INIT` macro.

Add a test comparing the main branch to itself, resulting in no diff.

Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Simon Marchi
2024-11-12 11:22:57 -05:00
committed by Junio C Hamano
parent b31fb630c0
commit 98e4015593
2 changed files with 6 additions and 4 deletions
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6
builtin/difftool.c
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@ -376,7 +376,8 @@ static int run_dir_diff(const char *extcmd, int symlinks, const char *prefix,
struct checkout lstate, rstate;
int err = 0;
struct child_process cmd = CHILD_PROCESS_INIT;
struct hashmap wt_modified, tmp_modified;
struct hashmap wt_modified = HASHMAP_INIT(path_entry_cmp, NULL);
struct hashmap tmp_modified = HASHMAP_INIT(path_entry_cmp, NULL);
int indices_loaded = 0;
workdir = repo_get_work_tree(the_repository);
@ -601,9 +602,6 @@ static int run_dir_diff(const char *extcmd, int symlinks, const char *prefix,
* in the common case of --symlinks and the difftool updating
* files through the symlink.
*/
hashmap_init(&wt_modified, path_entry_cmp, NULL, wtindex.cache_nr);
hashmap_init(&tmp_modified, path_entry_cmp, NULL, wtindex.cache_nr);
for (i = 0; i < wtindex.cache_nr; i++) {
struct hashmap_entry dummy;
const char *name = wtindex.cache[i]->name;