On Tue, Mar 06, 2012 at 03:57:27PM -0800, Darrick J. Wong wrote:
> Change libext2fs to read and write full-size inodes in preparation for the
> metadata checksumming patchset, which will require this. Due to ABI
> compatibility requirements, this change must be hidden from client programs.
>
> Signed-off-by: Darrick J. Wong <djwong@xxxxxxxxxx>
After applying this first patch, the e2fsprogs regression test suite
blew up spectacularly caused by the malloc-managed free lists pointers
getting corrupted:
*** glibc detected *** /usr/projects/e2fsprogs/e2fsprogs/build/debugfs/debugfs: free(): invalid next size (fast): 0x000000000063f9d0 ***
======= Backtrace: =========
/lib/libc.so.6(+0x77806)[0x7ffff6e4a806]
/lib/libc.so.6(cfree+0x73)[0x7ffff6e510d3]
/usr/projects/e2fsprogs/e2fsprogs/build/lib/libext2fs.so.2(ext2fs_free_mem+0x30)[0x7ffff7bb562f]
Interestingly, valgrind was *not* useful in finding the problem;
apparently it was getting confused by the ext2fs_get_mem()
abstraction, which is unfortunate. I'll have to look into that at
some point.
Anyway, the problem was in ext2fs_write_inode_full(), and it could be
replicated by simply writing to an inode, i.e.
mke2fs -F -O resize_inode -o Linux -b 1024 /tmp/image 16384
debugfs -w -R "set_inode_field <7> mtime now" /tmp/image
is enough to trigger it. The problem is with a 128 byte ext2 file
system, ext2fs_write_inode_full() is passed a large inode and so
bufsize is 156, but EXT2_INODE_SIZE(fs->super) is 128. So at
lib/ext2fs/inode.c:698:
memcpy(w_inode, inode, bufsize);
you end up writing 156 bytes into a memory buffer that was allocated
to a size of 128 bytes. Hilarity ensues.
The fix is relatively simple:
memcpy(w_inode, inode, (bufsize > length) ? length : bufsize);
Anyway, this is *why* running the regression tests are important.
(And why projects which don't have regression test suites are just
asking for trouble.)
They catch all sorts of interesting oversights like this....
- Ted
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