Re: [PATCH] ext4: fix uniniatilized extend splitting error.

Mingming Cao
2008-01-10T23:42:59Z

Thanks for catching this, I added your fix to the ext4 patch queue
http://repo.or.cz/w/ext4-patch-queue.git

On Thu, 2008-01-10 at 17:31 +0300, Dmitry Monakhov wrote:
> Hi,
> While playing with new fancy fallocate interface on ext4 i've triggered
> bug which corrupted my grub :).
>
> My testcase:
> ~~~~~~~~~~~~
> blksize = 0x1000;
> fd = open(argv[1], O_RDWR|O_CREAT, 0700);
> unsigned long long sz = 0x10000000UL;
> /* allocating big blocks chunk */
> syscall(__NR_fallocate, fd, 0, 0UL, sz)
>
> /* grab all other available filesystem space */
> tfd = open("tmp", O_RDWR|O_CREAT|O_DIRECT, 0700);
> while( write(tfd, buf, 4096) > 0); /* loop untill ENOSPC */
> fsync(fd); /* just in case */
> while (pos < sz) {
> /* each seek+ write operation result in splits uninitialized extent
> in three extents. Splitting may result in new extent allocation
> which probably will fail because of ENOSPC*/
>
> lseek(fd, blksize*2 -1, SEEK_CUR);
> if ((ret = write(fd, 'a', 1)) != 1)
> exit(1);
> pos += blksize * 2;
> }
>
> Buggy place:
> ~~~~~~~~~~~~
> ext4_ext_get_blocks(..., bh_result,..)
> {
> err = 0;
> allocated = 0;
> ....
> ret = ext4_ext_convert_to_initialized(...)
> if (ret < 0)
> << By occasion real error code was lost here.
> goto out2
> ....
> out2:
> ....
> return err? err: allocated;
> << Wow.. exit with "0", and caller assumes what bh_result was properly filled
> << and then will submit it for write. But in fact bh contains random data in
> << ->b_bdev, ->b_blocknr fileds :).
> }
>
> Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
> ---
> fs/ext4/extents.c | 5 +++--
> 1 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index 8528774..fc8e508 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -2320,9 +2320,10 @@ int ext4_ext_get_blocks(handle_t *handle, struct inode *inode,
> ret = ext4_ext_convert_to_initialized(handle, inode,
> path, iblock,
> max_blocks);
> - if (ret <= 0)
> + if (ret <= 0) {
> + err = ret;
> goto out2;
> - else
> + } else
> allocated = ret;
> goto outnew;
> }