Patch "ext4: fix SEEK_HOLE/SEEK_DATA for blocksize < pagesize" has been added to the 3.18-stable tree

This is a note to let you know that I've just added the patch titled

ext4: fix SEEK_HOLE/SEEK_DATA for blocksize < pagesize

to the 3.18-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
ext4-fix-seek_hole-seek_data-for-blocksize-pagesize.patch
and it can be found in the queue-3.18 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Jan Kara <[email protected]>
Date: Sat, 5 Aug 2017 17:43:24 -0400
Subject: ext4: fix SEEK_HOLE/SEEK_DATA for blocksize < pagesize

From: Jan Kara <[email protected]>

commit fcf5ea10992fbac3c7473a1db33d56a139333cd1 upstream.

ext4_find_unwritten_pgoff() does not properly handle a situation when starting index is in the middle of a page and blocksize < pagesize. The following command shows the bug on filesystem with 1k blocksize:

  xfs_io -f -c "falloc 0 4k" \
            -c "pwrite 1k 1k" \
            -c "pwrite 3k 1k" \
            -c "seek -a -r 0" foo

In this example, neither lseek(fd, 1024, SEEK_HOLE) nor lseek(fd, 2048, SEEK_DATA) will return the correct result.

Fix the problem by neglecting buffers in a page before starting offset.

---
 fs/ext4/file.c |    3 +++
 1 file changed, 3 insertions(+)

@@ -340,6 +340,8 @@ static int ext4_find_unwritten_pgoff(str
 				lastoff = page_offset(page);
 				bh = head = page_buffers(page);
 				do {
+					if (lastoff + bh->b_size <= startoff)
+						goto next;
 					if (buffer_uptodate(bh) ||
 					    buffer_unwritten(bh)) {
 						if (whence == SEEK_DATA)

@@ -354,6 +356,7 @@ static int ext4_find_unwritten_pgoff(str
 						unlock_page(page);
 						goto out;
 					}
+next:
 					lastoff += bh->b_size;
 					bh = bh->b_this_page;
 				} while (bh != head);

Patches currently in stable-queue which might be from [email protected] are

queue-3.18/ext4-fix-seek_hole-seek_data-for-blocksize-pagesize.patch