Re: [BUG] git stash show -p with invalid option aborts with double-free in show_stash() (strvec_clear)
From: Jeff King <hidden>
Date: 2025-09-19 16:48:23
On Fri, Sep 19, 2025 at 09:00:12AM -0700, Junio C Hamano wrote:
quoted hunk ↗ jump to hunk
The easier, more performant, and closer to the original design around the revisions API is to do this:diff --git c/builtin/stash.c w/builtin/stash.c index f5ddee5c7f..b6312b1b70 100644 --- c/builtin/stash.c +++ w/builtin/stash.c@@ -1016,6 +1016,8 @@ static int show_stash(int argc, const char **argv, const char *prefix, } argc = setup_revisions(revision_args.nr, revision_args.v, &rev, NULL); + for (i = argc; i < revision_args.nr; i++) + revision_args.v[i] = NULL; if (argc > 1) goto usage; if (!rev.diffopt.output_format) {
I think we'll have leaked the string holding "-p" in this instance, though. We probably need to pass in a setup_revision_opt struct with its free_removed_argv_elements flag set. That's true even without your patch, too, of course. I'm mildly surprised that the test suite doesn't hit this in leak-checking mode, since it is a problem any time we rearrange argv. E.g., I think: git stash show -p -- leaks (I was surprised that "stash show -p --stat" didn't leak, but it doesn't seem to rearrange?). Another interesting thing about your patch above is that it fills the strvec with a bunch of NULL entries. Which happens to work, because free(NULL) is a noop, but I think may be subtly violating assumptions made about strvecs. Probably: revision_args.nr = setup_revisions(...); fits my mental model better, though that is violating a different strvec invariant now (that the .v[.nr] is always NULL). I think setup_revisions() is a little sloppy not to set argv[argc] to NULL itself.
A less performant but may in the longer term safer alternative is to
change the caller-callee contract around setup_revisions() so that
the later "unused" slots in the argv array is NULLed before
returning to the caller, i.e. instead of leaving
.v = { "show", "--no-such-option", "--no-such-option", NULL }
in the revision_args.v[] array, teach setup_revisions() to leave
.v = { "show", "--no-such-option", NULL, NULL }
there (again, we cannot do anything about .nr that is only available
to the caller).
I think we should consider a fix like this. Grepping for the
free_removed_argv_elements option, there are a few other spots that
correctly use that flag, but aren't updating the strvec argc. E.g.,
bisect_rev_setup(). So they're going to run into the same problem.
I wonder if the best solution is a setup_revisions() wrapper for strvecs
that will:
- turn on the free_removed_argv_elements option automatically
- collect the return value of setup_revisions() and use it to fix
the .nr field of the strvec
- restore the NULL invariant at the end of the array (though I would
also be happy if setup_revisions() just did this itself)
-Peff