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Re: Oops.

From: Philip Martin <philip_at_codematters.co.uk>
Date: 2003-02-10 17:51:03 CET

mark benedetto king <mbk@boredom.org> writes:

> I see that you've done
> *uuid = apr_pstrmemdup(trail->pool, value.data, value.size + 1);
> It is my impression that BDB makes no guarantees about what the value
> of the byte at value.data[value.size] is. It might not be NUL, and
> I'm pretty sure I've seen it as ' '.
> Anyway, because of this I went and actually *looked* at apr_pstrmemdup(),
> and I'll bet the right thing to do is change this to
> *uuid = apr_pstrmemdup(trail->pool, value.data, value.size);
> because apr_pstrmemdup() automatically allocates N+1 bytes and NUL-terminates.

I'm using Subversion r4816

$ svnadmin create repo
$ valgrind -q svnadmin dump repo > zz
==30155== Invalid read of size 1
==30155== at 0x40048090: memcpy (/home/pm/sw/valgrind-1.0.4/vg_clientfuncs.c:496)
==30155== by 0x40390947: apr_pstrmemdup (apr_strings.c:147)
==30155== by 0x4026848B: svn_fs__bdb_get_uuid (../svn/subversion/libsvn_fs/bdb/uuids-table.c:109)
==30155== by 0x4027BAC4: txn_body_get_uuid (../svn/subversion/libsvn_fs/uuid.c:38)
==30155== Address 0x430D430C is 0 bytes after a block of size 36 alloc'd
==30155== at 0x400476BB: malloc (/home/pm/sw/valgrind-1.0.4/vg_clientfuncs.c:100)
==30155== by 0x403422EE: __os_malloc_4000 (in /usr/lib/libdb-4.0.so)
==30155== by 0x4034236F: __os_realloc_4000 (in /usr/lib/libdb-4.0.so)
==30155== by 0x40317462: __db_retcopy_4000 (in /usr/lib/libdb-4.0.so)
* Dumped revision 0.

Which implies two things: first the +1 is indeed wrong, and second you
are not setting the correct flags to use the local stack based buffer
in svn_fs__bdb_get_uuid. You need to specify DB_DBT_USERMEM and set
ulen. Why use stack memory at all? If you use pool memory directly,
then you don't need to copy it.

Philip Martin
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Received on Mon Feb 10 17:52:06 2003

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