linux-ext4 - [PATCH] ext4: fix uniniatilized extend splitting error.

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Date:	Thu, 10 Jan 2008 17:31:42 +0300
From:	Dmitry Monakhov <dmonakhov@...nvz.org>
To:	linux-ext4@...r.kernel.org
Cc:	Andreas Dilger <adilger@...sterfs.com>
Subject: [PATCH] ext4: fix uniniatilized extend splitting error.

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@...nvz.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


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