Date: Tue, 14 Dec 2004 05:57:38 +1100 From: Peter Jeremy <PeterJeremy@optushome.com.au> To: henry <henry@jot.to> Cc: freebsd-hackers@freebsd.org Subject: Re: du(1)/fts(3) integer overflow Message-ID: <20041213185738.GD79646@cirb503493.alcatel.com.au> In-Reply-To: <200412131142.iBDBgMp4082138@mail.squidge.com> References: <200412131142.iBDBgMp4082138@mail.squidge.com>
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On Mon, 2004-Dec-13 11:42:17 -0000, henry wrote:
>I have noticed a problem with the fts(3) library or the way du(1) interacts
>with it.
>
>A 3.2TiB file gives the following output:
>> du -cs /fs/file
>3408720016 /fs/file
>-886247279 total
>
>This is because while stat(2) reports blocks as a 64bit number du(1) uses
>the 32bit value FTSENT.fts_number to store the result:
I think the large filesystem support is insufficiently exercised and
there will probably be more of these sort of things lurking around.
>The simplest change appears to be to make fts_number 64bit however this
>changes the fts(3) abi, so I am not sure if this is acceptable.
For 6.x, the ABI isn't fixed so fts_number can be changed to int64_t.
4.x doesn't really support large filesystems due to integer overflow
issues in UFS/FFS code so it's not really a problem there.
The 5.x ABI is fixed so there's no simple solution there. Possible hacks
would be:
- Add a new 'fts_number64' at the end of FTSENT. Since FTSENT is always
managed by fts(3) and the documentation allows for undocumented fields,
this should be permitted, though a "new" du(1) with an "old" libc
would break badly.
- Move fts_number to the end of FTSENT and leave a 'long' hole where the
existing fts_number is. This changes the ABI but old programs remain
compatible with the new fts. (Though new programs break with the
old fts).
- <Severe_kludge_alert>Have du(1) treat fts_pointer as an integer that
it can concatenate to fts_number on 32-bit architectures:
int64_t x = (int64_t)(ulong)p->fts_parent->fts_number |
((int64_t)(ulong)p->fts_parent->fts_pointer) << 32;
x += p->fts_statp->st_blocks;
p->fts_parent->fts_number = (long)x;
p->fts_parent->fts_pointer = (void *)(long)(x >> 32);
etc. </Severe_kludge_alert>
--
Peter Jeremy
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