Re: [PATCH] reflog: close leak of reflog expire entry

On Wed, Jul 09, 2025 at 02:49:14PM -0700, Jacob Keller wrote:

find_cfg_ent() allocates a struct reflog_expire_entry_option via
FLEX_ALLOC_MEM and returns its pointer to reflog_expire_config(). The
function exits without freeing the memory:

Direct leak of 39 byte(s) in 1 object(s) allocated from:
    #0 0x7ff975ee6883 in calloc (/lib64/libasan.so.8+0xe6883)
    #1 0x0000010edada in xcalloc ../wrapper.c:154
    #2 0x000000df0898 in find_cfg_ent ../reflog.c:28
    #3 0x000000df0898 in reflog_expire_config ../reflog.c:70
    #4 0x00000095c451 in configset_iter ../config.c:2116
    #5 0x0000006d29e7 in git_config ../config.h:724
    #6 0x0000006d29e7 in cmd_reflog_expire ../builtin/reflog.c:205
    #7 0x0000006d504c in cmd_reflog ../builtin/reflog.c:419
    #8 0x0000007e4054 in run_builtin ../git.c:480
    #9 0x0000007e4054 in handle_builtin ../git.c:746
    #10 0x0000007e8a35 in run_argv ../git.c:813
    #11 0x0000007e8a35 in cmd_main ../git.c:953
    #12 0x000000441e8f in main ../common-main.c:9
    #13 0x7ff9754115f4 in __libc_start_call_main (/lib64/libc.so.6+0x35f4)
    #14 0x7ff9754116a7 in __libc_start_main@@GLIBC_2.34 (/lib64/libc.so.6+0x36a7)
    #15 0x000000444184 in _start (/home/jekeller/libexec/git-core/git+0x444184)

Close this leak by freeing the entry pointer on exit of the
reflog_expire_config() function. This frees both the entry structure and
its embedded pattern array thanks to the use of FLEX_ALLOC_MEM.

Hmm, this can't be right, can it? The end of reflog_expire_config()
looks like this:

        ent = find_cfg_ent(opts, pattern, pattern_len);
        if (!ent)
                return -1;
        switch (slot) {
        case REFLOG_EXPIRE_TOTAL:
                ent->expire_total = expire;
                break;
        case REFLOG_EXPIRE_UNREACH:
                ent->expire_unreachable = expire;
                break;
        }
        return 0;

So if we free(ent), then what was the point of the function? We'd set
some fields in it and then throw it away?

And indeed, find_cfg_ent() seems to add the newly allocated entry to the
list opt->entries list. So by freeing here, we're leaving a dangling
pointer in that list.

Probably that list needs to be cleaned up when cmd_reflog_expire()
finishes?

-Peff