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Commit fcf5ea10 authored by Jan Kara's avatar Jan Kara Committed by Theodore Ts'o
Browse files

ext4: fix SEEK_HOLE/SEEK_DATA for blocksize < pagesize 



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.

Reported-by: default avatarAndreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
Signed-off-by: default avatarJan Kara <jack@suse.cz>
CC: stable@vger.kernel.org # 3.8+
parent e4510577

fs/ext4/file.c

+3 −0
Original line number Diff line number Diff line
@@ -537,6 +537,8 @@ static int ext4_find_unwritten_pgoff(struct inode *inode, 
				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)
@@ -551,6 +553,7 @@ static int ext4_find_unwritten_pgoff(struct inode *inode, 
						unlock_page(page);

						goto out;

					}

next:

					lastoff += bh->b_size;

					bh = bh->b_this_page;

				} while (bh != head);