Trying to upgrade our replica pairs to 1.2.1, i started from a fresh slave (no initial data) running with the following command line:

/opt/mongodb-linux-x86_64-1.2.1/bin/mongod --dbpath=/mongo/data --nssize 160 --noauth --pairwith=production-shard1-001

After a while (about 30GB cloned), the slave issue the following message:

Tue Jan 26 09:38:12 Assertion: Invalid dbref/code/string/symbol size
skipping corrupt object from production.messages_dxxxxxxxxxxxxxxxxxx
Tue Jan 26 09:38:33 invalid object size: 11031214
Tue Jan 26 09:38:33 Assertion: Invalid BSONObj spec size
Tue Jan 26 09:38:33 repl: AssertionException Invalid BSONObj spec size
Tue Jan 26 09:38:33 repl: sleep 2sec before next pass

Given the delay between the first message (38:12) and the next one (38:33), i'm not even sure the object that cause the error is in this collection. I thought that 1.2.1 would report this error including the _id of the culprit and just go on ... this is not the case, strace on the mongod process shows that it is just sitting there on a wait4 call:

Process 8175 attached - interrupt to quit
wait4(-1,
...

As 1.1.3 doesn't have the newly introduced bsonsize() api call, how can i identify and get rid of those invalid objects in the master's database ?