Re: [PATCH v4] fs: Fix page_mkwrite off-by-one errors

Jeff Layton
2020-01-09T13:35:03Z

On Wed, 2020-01-08 at 14:15 +0100, Andreas Gruenbacher wrote:
> Hi Darrick,
>
> here's an updated version with the latest feedback incorporated. Hope
> you find that useful.
>
> As far as the f2fs merge conflict goes, I've been told by Linus not to
> resolve those kinds of conflicts but to point them out when sending the
> merge request. So this shouldn't be a big deal.
>
> Changes:
>
> * Turn page_mkwrite_check_truncate into a non-inline function.
> * Get rid of now-unused mapping variable in ext4_page_mkwrite.
> * In btrfs_page_mkwrite, don't ignore the return value of
> block_page_mkwrite_return (no change in behavior).
> * Clean up the f2fs_vm_page_mkwrite changes as suggested by
> Jaegeuk Kim.
>
> Thanks,
> Andreas
>
> --
>
> The check in block_page_mkwrite that is meant to determine whether an
> offset is within the inode size is off by one. This bug has been copied
> into iomap_page_mkwrite and several filesystems (ubifs, ext4, f2fs,
> ceph).
>
> Fix that by introducing a new page_mkwrite_check_truncate helper that
> checks for truncate and computes the bytes in the page up to EOF. Use
> the helper in the above mentioned filesystems.
>
> In addition, use the new helper in btrfs as well.
>
> Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
> Acked-by: David Sterba <dsterba@suse.com> (btrfs)
> Acked-by: Richard Weinberger <richard@nod.at> (ubifs)
> Acked-by: Theodore Ts'o <tytso@mit.edu> (ext4)
> Acked-by: Chao Yu <yuchao0@huawei.com> (f2fs)
> ---
> fs/btrfs/inode.c | 16 +++++-----------
> fs/buffer.c | 16 +++-------------
> fs/ceph/addr.c | 2 +-
> fs/ext4/inode.c | 15 ++++-----------
> fs/f2fs/file.c | 19 +++++++------------
> fs/iomap/buffered-io.c | 18 +++++-------------
> fs/ubifs/file.c | 3 +--
> include/linux/pagemap.h | 2 ++
> mm/filemap.c | 28 ++++++++++++++++++++++++++++
> 9 files changed, 56 insertions(+), 63 deletions(-)
>
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index e3c76645cad7..23e6f614e000 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -9011,16 +9011,15 @@ vm_fault_t btrfs_page_mkwrite(struct vm_fault *vmf)
> goto out_noreserve;
> }
>
> - ret = VM_FAULT_NOPAGE; /* make the VM retry the fault */
> again:
> lock_page(page);
> - size = i_size_read(inode);
>
> - if ((page->mapping != inode->i_mapping) ||
> - (page_start >= size)) {
> - /* page got truncated out from underneath us */
> + ret2 = page_mkwrite_check_truncate(page, inode);
> + if (ret2 < 0) {
> + ret = block_page_mkwrite_return(ret2);
> goto out_unlock;
> }
> + zero_start = ret2;
> wait_on_page_writeback(page);
>
> lock_extent_bits(io_tree, page_start, page_end, &cached_state);
> @@ -9041,6 +9040,7 @@ vm_fault_t btrfs_page_mkwrite(struct vm_fault *vmf)
> goto again;
> }
>
> + size = i_size_read(inode);
> if (page->index == ((size - 1) >> PAGE_SHIFT)) {
> reserved_space = round_up(size - page_start,
> fs_info->sectorsize);
> @@ -9073,12 +9073,6 @@ vm_fault_t btrfs_page_mkwrite(struct vm_fault *vmf)
> }
> ret2 = 0;
>
> - /* page is wholly or partially inside EOF */
> - if (page_start + PAGE_SIZE > size)
> - zero_start = offset_in_page(size);
> - else
> - zero_start = PAGE_SIZE;
> -
> if (zero_start != PAGE_SIZE) {
> kaddr = kmap(page);
> memset(kaddr + zero_start, 0, PAGE_SIZE - zero_start);
> diff --git a/fs/buffer.c b/fs/buffer.c
> index d8c7242426bb..53aabde57ca7 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -2499,23 +2499,13 @@ int block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
> struct page *page = vmf->page;
> struct inode *inode = file_inode(vma->vm_file);
> unsigned long end;
> - loff_t size;
> int ret;
>
> lock_page(page);
> - size = i_size_read(inode);
> - if ((page->mapping != inode->i_mapping) ||
> - (page_offset(page) > size)) {
> - /* We overload EFAULT to mean page got truncated */
> - ret = -EFAULT;
> + ret = page_mkwrite_check_truncate(page, inode);
> + if (ret < 0)
> goto out_unlock;
> - }
> -
> - /* page is wholly or partially inside EOF */
> - if (((page->index + 1) << PAGE_SHIFT) > size)
> - end = size & ~PAGE_MASK;
> - else
> - end = PAGE_SIZE;
> + end = ret;
>
> ret = __block_write_begin(page, 0, end, get_block);
> if (!ret)
> diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c
> index 7ab616601141..ef958aa4adb4 100644
> --- a/fs/ceph/addr.c
> +++ b/fs/ceph/addr.c
> @@ -1575,7 +1575,7 @@ static vm_fault_t ceph_page_mkwrite(struct vm_fault *vmf)
> do {
> lock_page(page);
>
> - if ((off > size) || (page->mapping != inode->i_mapping)) {
> + if (page_mkwrite_check_truncate(page, inode) < 0) {
> unlock_page(page);
> ret = VM_FAULT_NOPAGE;
> break;

You can add my Acked-by on the ceph part.

--
Jeff Layton <jlayton@kernel.org>