Attachment 153209 Details for Bug 237326 – kernel patch

[patch] kernel patch

md_bitmap_read_past_end_of_file.diff (text/plain), 3.25 KB, created by Paul Clements on 2007-04-20 20:06:10 UTC

(hide)

Description:

Filename:

MIME Type:

Creator: Paul Clements

Created: 2007-04-20 20:06:10 UTC

Size: 3.25 KB

patch

obsolete

>On Monday January 22, yinyang801120@gmail.com wrote:
>> If the bitmap size is less than one page including super_block and
>> bitmap and the inode's i_blkbits is also small, when doing the
>> read_page function call to read the sb_page, it may return a error.
>> For example, if the device is 12800 chunks, its bitmap file size is
>> about 1.6KB include the bitmap super block. But the inode i_blkbits
>> value of the bitmap file is 10,  the read_page will submit 4 bh to
>> load the sb_page. Because the size of bitmap is only 1.6KB, in the
>> while loop, the error will ocurr when do bmap operation for the block
>> 2, which will  return 0. Then the bitmap can't be initated because of
>> ther read sb page fail.
>> 
>> Another error is in the bitmap_init_from_disk function.  Before doing
>> read_page,. calculating the count value misses the size of super
>> block. When the bitmap just needs one page, It will read two pages
>> adding the super block. But at the second read, the count value will
>> be set to 0, and not all the bitmap will be read from the disk and
>> some bitmap will missed at the second page.
>> 
>> I give a patch as following:
>
>Thanks a lot for this.
>Rather than checking the file size in read_page, I would like to make
>sure the 'count' that is passed in never exceeds the size of the
>file.  This should have the same effect.
>
>So this is that patch I plan to submit.
>
>Thanks again,
>NeilBrown
>
>
>------------------
>Avoid reading past the end of a bitmap file.
>
>In most cases we check the size of the bitmap file before
>reading data from it.  However when reading the superblock,
>we always read the first PAGE_SIZE bytes, which might not 
>always be appropriate.  So limit that read to the size of the
>file if appropriate.
>
>Also, we get the count of available bytes wrong in one place,
>so that too can read past the end of the file.
>
>Cc:  "yang yin" <yinyang801120@gmail.com>
>Signed-off-by: Neil Brown <neilb@suse.de>
>
>### Diffstat output
> ./drivers/md/bitmap.c |   12 ++++++++----
> 1 file changed, 8 insertions(+), 4 deletions(-)
>
>diff .prev/drivers/md/bitmap.c ./drivers/md/bitmap.c
>--- .prev/drivers/md/bitmap.c	2007-01-23 09:44:11.000000000 +1100
>+++ ./drivers/md/bitmap.c	2007-01-23 09:44:59.000000000 +1100
>@@ -479,9 +479,12 @@ static int bitmap_read_sb(struct bitmap 
> 	int err = -EINVAL;
> 
> 	/* page 0 is the superblock, read it... */
>-	if (bitmap->file)
>-		bitmap->sb_page = read_page(bitmap->file, 0, bitmap, PAGE_SIZE);
>-	else {
>+	if (bitmap->file) {
>+		loff_t isize = i_size_read(bitmap->file->f_mapping->host);
>+		int bytes = isize > PAGE_SIZE ? PAGE_SIZE : isize;
>+
>+		bitmap->sb_page = read_page(bitmap->file, 0, bitmap, bytes);
>+	} else {
> 		bitmap->sb_page = read_sb_page(bitmap->mddev, bitmap->offset, 0);
> 	}
> 	if (IS_ERR(bitmap->sb_page)) {
>@@ -877,7 +880,8 @@ static int bitmap_init_from_disk(struct 
> 			int count;
> 			/* unmap the old page, we're done with it */
> 			if (index == num_pages-1)
>-				count = bytes - index * PAGE_SIZE;
>+				count = bytes + sizeof(bitmap_super_t)
>+					- index * PAGE_SIZE;
> 			else
> 				count = PAGE_SIZE;
> 			if (index == 0) {
>-
>To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
>the body of a message to majordomo@vger.kernel.org
>More majordomo info at  http://vger.kernel.org/majordomo-info.html
>Please read the FAQ at  http://www.tux.org/lkml/

Actions: View | Diff

Attachments on bug 237326: 153209