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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: Andreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Jan Kara <jack@suse.cz>
CC: stable@vger.kernel.org # 3.8+
This commit is contained in:
Jan Kara 2017-08-05 17:43:24 -04:00 committed by Theodore Ts'o
parent e45105772d
commit fcf5ea1099
1 changed files with 3 additions and 0 deletions
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3
fs/ext4/file.c
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@ -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);