remote_get_heads: reference length limit

I've been having trouble with git push apparently resending the entire commit trace for the branch each and every time I push. Poking at the source it seems this is due to a length limit on reference names as pulled from the remote repository.

When we are building the pack to send we are sent a list of remote heads. get_remote_heads() reads these in, validates them and finally adds them to the remote_refs list. Part of the validation is a simple check for size and form; check_ref().

static int check_ref(const char *name, int len, unsigned int flags)

{
        if (!flags)
                return 1;

        if (len > 45 || memcmp(name, "refs/", 5))
                return 0;

[...]
}

With the refs/heads/ prefix included this limits the head names to 34 characters. From what I can see there is no good reason for this limit to be so low. I can see we don't want the remote end bloating us out of control, but we are already limiting the lines which contain these references to 1000 bytes and making no attempt to limit the number of them the remote server can send us. There seems to be no limits imposed on the name length other than MAX_PATHLEN.

Can anyone see a reason to keep this (len > 45) check?

-apw

Yes, it was a mis-conversion done with commit 2718ff0. The data this part (and the caller) is dealing with are peek-remote output (40-byte hex object name, tab and "refs/..."). Before that commit we had a check like this:

+ if (ignore_funny && 45 < len && !memcmp(name, "refs/", 5) &&
+ check_ref_format(name + 5))
+ continue;

That is, "if we are ignoring funny fake refs, continue when the name begins with refs/ and is magic (e.g. refs/heads/master^{}); by the way that can only happen if the entire line length is more than 45 bytes (because of 40-byte hex plus tab, anything shorter than that cannot even fit "refs/" at the beginning of the name).

But when the check_ref() function was written it was made to take the name length as "len", so I do not think there is a reason to check the name against 45 at all. Also the direction of the comparison is wrong in the new code. It was meant to be "line must be at least this long otherwise it is not right".

I think you can just drop "len > 45 || " part.

send-pack: remove remote reference limit

When build a pack for a push we query the remote copy for existant heads. These are used to prune unnecessary objects from the pack. As we receive the remote references in get_remote_heads() we validate the reference names via check_ref() which includes a length check; rejecting those >45 characters in size.

This is a miss converted change, it was originally designed to reject messages which were less than 45 characters in length (a 40 character sha1 and refs/) to prevent comparing unitialised memory. check_ref() now gets the raw length so check for at least 5 characters.

---

index e501ccc..371aea1 100644
@@ -17,7 +17,7 @@ static int check_ref(const char *name, i
 	if (!flags)
 		return 1;
 
-	if (len > 45 || memcmp(name, "refs/", 5))
+	if (len < 5 || memcmp(name, "refs/", 5))
 		return 0;
 
 	/* Skip the "refs/" part */