http://sourceware.org/bugzilla/show_bug.cgi?id=13534
Bug #: 13534
Summary: ar mishandles files bigger than 2GB
Product: binutils
Version: 2.23 (HEAD)
Status: NEW
Severity: normal
Priority: P2
Component: binutils
AssignedTo: unassig...@sourceware.org
ReportedBy: fgou...@codeweavers.com
Classification: Unclassified
Here is how to reproduce the problem:
$ dd if=/dev/zero of=file2G bs=1M count=2049
2049+0 records in
2049+0 records out
2148532224 bytes (2.1 GB) copied, 47.9032 s, 44.9 MB/s
$ ar q ar2G.ar file2G
$ od -a ar2G.ar
0000000 ! < a r c h > nl f i l e 2 G / sp
0000020 sp sp sp sp sp sp sp sp 1 3 2 4 4 6 6 2
0000040 8 0 sp sp 1 0 0 0 sp sp 1 0 0 0 sp sp
0000060 1 0 0 6 4 4 sp sp - 2 1 4 6 4 3 5
0000100 0 7 ` nl nul nul nul nul nul nul nul nul nul nul nul nul
^C
Note that the archive claims that the 'file2G' size is negative:
-214643507. This results in an invalid archive that cannot be extracted:
$ ar xv ar2G.ar
x - file2G
ar: ar2G.ar is not a valid archive
As a consequence of this it is impossible to generate Debian packages
bigger than 2GB (for instance for applications that have a large
dataset).
Obviously the file size was stored into a signed 32bit variable. Reading
the source code shows that it was actually a long which means there will
be further issues if such an archive is moved from a 32bit system to a
64bit one.
More precisely, the archive file format is a linked list of element
headers and relies on these having accurate size information to find the
position of the next element header. Since the archive format allocates
10 characters for the file size, it should be able to handle files up to
10GB. However:
* Files between 2GiB and 4GiB
The file size is stored as being negative. The archive cannot be
extracted by either the 32bit ar or the 64bit one.
* Files between 4GiB and 10GB
Only the first 32bits are taken into account so ar will write a size
of 0.1GiB for a 4.1GiB file. As a result, during extraction ar will
think there is an archive element header in the middle of the file,
resulting in an error (if not worse).
There are also sign issues between 6GiB and 8GiB.
* Files bigger than 10GB
ar will silently truncated the file size to its first 10 decimal
digits. Decoding will fail for the same reason as above.
Even 64bit systems are not immune to these issues due to the file sizes
being stored in 'unsigned int' variables in various places.
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