Re: [PATCH] [RFC] sparse index: fix use-after-free bug in cache_tree_verify()

"Phillip Wood via GitGitGadget" [off-list ref] writes:

/*
 * Please document what the values that can be returned from
 * this function are and what they mean, just before this
 * funciton.  I am guessing that this is "all bets are off and
 * you need to redo the computation again over the full in-core
 * index"?  It is not an error and I think it makes sense to use
 * positive 1 like this patch does instead of -1.
 */

 
-static void verify_one(struct repository *r,
-		       struct index_state *istate,
-		       struct cache_tree *it,
-		       struct strbuf *path)
+static int verify_one(struct repository *r,
+		      struct index_state *istate,
+		      struct cache_tree *it,
+		      struct strbuf *path)
 {

This is just a style thing, but I would find it easier to follow if
it just recursed into itself, i.e.

-	verify_one(...);
+	if (verify_one(...))
+		cache_tree_verify(r, istate);

or

-	verify_one(...);
+	again:
+	if (verify_one(...))
+		strbuf_reset(&path);
+		goto again;
}	}

On the other hand, if the new code wants to say "I would retry at
most once, otherwise there is something wrong in me", then

-	verify_one(r, istate, istate->cache_tree, &path);
+	if (verify_one(r, istate, istate->cache_tree, &path)) {
+		strbuf_reset(&path);
+		if (verify_one(r, istate, istate->cache_tree, &path))
+			BUG("...");
+	}

would be better.

Other than that, nicely done.

On 10/6/2021 3:17 PM, Junio C Hamano wrote:

"Phillip Wood via GitGitGadget" [off-list ref] writes:

quoted

@@ -907,6 +917,9 @@ void cache_tree_verify(struct repository *r, struct index_state *istate)
 
 	if (!istate->cache_tree)
 		return;
-	verify_one(r, istate, istate->cache_tree, &path);
+	if (verify_one(r, istate, istate->cache_tree, &path)) {
+		strbuf_reset(&path);
+		verify_one(r, istate, istate->cache_tree, &path);
+	}
 	strbuf_release(&path);
 }

This is just a style thing, but I would find it easier to follow if
it just recursed into itself, i.e.

-	verify_one(...);
+	if (verify_one(...))
+		cache_tree_verify(r, istate);

or

-	verify_one(...);
+	again:
+	if (verify_one(...))
+		strbuf_reset(&path);
+		goto again;
}	}

On the other hand, if the new code wants to say "I would retry at
most once, otherwise there is something wrong in me", then

quoted

-	verify_one(r, istate, istate->cache_tree, &path);
+	if (verify_one(r, istate, istate->cache_tree, &path)) {
+		strbuf_reset(&path);
+		if (verify_one(r, istate, istate->cache_tree, &path))
+			BUG("...");
+	}

would be better.

I'm in favor of this second option.

Thanks,
-Stolee