[PATCH] ext4: fix uniniatilized extend splitting error.

Dmitry Monakhov
2008-01-10T14:34:30Z

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;
}
--
1.5.3.1.40.g6972-dirty