Crash in CLEAR_IF_FIRST handling in tdb

[Volker Lendecke]

On Thu, Oct 04, 2012 at 10:03:58AM +0200, Volker Lendecke wrote:
> > > Under
> > > http://git.samba.org/?p=vl/samba.git/.git;a=shortlog;h=refs/heads/tdb
> > > find a patchset that for me fixes a crash in winbind in tdb.
> > > For the explanation, see the second patch from the top.
> > 
> > Good catch!
> > 
> > Your fix here should stop a crash when accessing the header, but the
> > rest of the mmaped database is still going to cause SEGV, no?  We only
> > re-map it when we see an offset which is out-of-bounds (vs the
> > locally-cache tdb->map_size variable).
> 
> I believe we are okay with the fix. Whenever we access the
> mmap area pointed to by the hash pointed to by the hash
> sources, we lock the hash chain. I think we never keep
> information beyond a F_UNLK. Because tdb_new_database
> establishes an empty and correct database, tdb_fetch will
> never randomly access memory beyond the current file limit.
> The freelist is also set up with a short database in mind.
> So whenever there is a need to go beyond the file size,
> which might be shorter than the current mmap size, we will
> end up in tdb_expand, which now should deal fine with a
> shrunk file.

Just updated the above branch with code that survived
autobuild.

Volker

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