Re: [PATCH v3] fs: Fix page_mkwrite off-by-one errors

From: Chao Yu
Date: Wed Jan 08 2020 - 04:09:30 EST

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On 2020/1/8 7:20, Darrick J. Wong wrote:
> On Wed, Dec 18, 2019 at 02:09:35PM +0100, Andreas Gruenbacher wrote:
>> Hi Darrick,
>>
>> can this fix go in via the xfs tree?
>>
>> 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@xxxxxxxxxx>
>> Acked-by: David Sterba <dsterba@xxxxxxxx> (btrfs part)
>> Acked-by: Richard Weinberger <richard@xxxxxx> (ubifs part)
>> ---
>> fs/btrfs/inode.c | 15 ++++-----------
>> fs/buffer.c | 16 +++-------------
>> fs/ceph/addr.c | 2 +-
>> fs/ext4/inode.c | 14 ++++----------
>> fs/f2fs/file.c | 19 +++++++------------
>
> Well, the f2fs developers never acked this and there was a conflict when
> I put this into for-next, so I removed the f2fs part (and fixed the
> unused variable warning in the ext4 part)...

Sorry for late reply.

Acked-by: Chao Yu <yuchao0@xxxxxxxxxx>

BTW, to avoid such conflict, does f2fs need to rebase/fix its last code
on current patch?

Thanks,

>
> --D
>
>> fs/iomap/buffered-io.c | 18 +++++-------------
>> fs/ubifs/file.c | 3 +--
>> include/linux/pagemap.h | 28 ++++++++++++++++++++++++++++
>> 8 files changed, 53 insertions(+), 62 deletions(-)
>>
>> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
>> index 56032c518b26..86c6fcd8139d 100644
>> --- a/fs/btrfs/inode.c
>> +++ b/fs/btrfs/inode.c
>> @@ -9016,13 +9016,11 @@ vm_fault_t btrfs_page_mkwrite(struct vm_fault *vmf)
>> 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)
>> goto out_unlock;
>> - }
>> + zero_start = ret2;
>> wait_on_page_writeback(page);
>>
>> lock_extent_bits(io_tree, page_start, page_end, &cached_state);
>> @@ -9043,6 +9041,7 @@ 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);
>> @@ -9075,12 +9074,6 @@ 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;
>> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
>> index 28f28de0c1b6..51ab1d2cac80 100644
>> --- a/fs/ext4/inode.c
>> +++ b/fs/ext4/inode.c
>> @@ -5871,7 +5871,6 @@ vm_fault_t ext4_page_mkwrite(struct vm_fault *vmf)
>> {
>> struct vm_area_struct *vma = vmf->vma;
>> struct page *page = vmf->page;
>> - loff_t size;
>> unsigned long len;
>> int err;
>> vm_fault_t ret;
>> @@ -5907,18 +5906,13 @@ vm_fault_t ext4_page_mkwrite(struct vm_fault *vmf)
>> }
>>
>> lock_page(page);
>> - size = i_size_read(inode);
>> - /* Page got truncated from under us? */
>> - if (page->mapping != mapping || page_offset(page) > size) {
>> + err = page_mkwrite_check_truncate(page, inode);
>> + if (err < 0) {
>> unlock_page(page);
>> - ret = VM_FAULT_NOPAGE;
>> - goto out;
>> + goto out_ret;
>> }
>> + len = err;
>>
>> - if (page->index == size >> PAGE_SHIFT)
>> - len = size & ~PAGE_MASK;
>> - else
>> - len = PAGE_SIZE;
>> /*
>> * Return if we have all the buffers mapped. This avoids the need to do
>> * journal_start/journal_stop which can block and take a long time
>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>> index 85af112e868d..0e77b2e6f873 100644
>> --- a/fs/f2fs/file.c
>> +++ b/fs/f2fs/file.c
>> @@ -51,7 +51,7 @@ static vm_fault_t f2fs_vm_page_mkwrite(struct vm_fault *vmf)
>> struct inode *inode = file_inode(vmf->vma->vm_file);
>> struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
>> struct dnode_of_data dn = { .node_changed = false };
>> - int err;
>> + int offset, err;
>>
>> if (unlikely(f2fs_cp_error(sbi))) {
>> err = -EIO;
>> @@ -70,13 +70,14 @@ static vm_fault_t f2fs_vm_page_mkwrite(struct vm_fault *vmf)
>> file_update_time(vmf->vma->vm_file);
>> down_read(&F2FS_I(inode)->i_mmap_sem);
>> lock_page(page);
>> - if (unlikely(page->mapping != inode->i_mapping ||
>> - page_offset(page) > i_size_read(inode) ||
>> - !PageUptodate(page))) {
>> + err = -EFAULT;
>> + if (likely(PageUptodate(page)))
>> + err = page_mkwrite_check_truncate(page, inode);
>> + if (unlikely(err < 0)) {
>> unlock_page(page);
>> - err = -EFAULT;
>> goto out_sem;
>> }
>> + offset = err;
>>
>> /* block allocation */
>> __do_map_lock(sbi, F2FS_GET_BLOCK_PRE_AIO, true);
>> @@ -101,14 +102,8 @@ static vm_fault_t f2fs_vm_page_mkwrite(struct vm_fault *vmf)
>> if (PageMappedToDisk(page))
>> goto out_sem;
>>
>> - /* page is wholly or partially inside EOF */
>> - if (((loff_t)(page->index + 1) << PAGE_SHIFT) >
>> - i_size_read(inode)) {
>> - loff_t offset;
>> -
>> - offset = i_size_read(inode) & ~PAGE_MASK;
>> + if (offset != PAGE_SIZE)
>> zero_user_segment(page, offset, PAGE_SIZE);
>> - }
>> set_page_dirty(page);
>> if (!PageUptodate(page))
>> SetPageUptodate(page);
>> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
>> index d33c7bc5ee92..1aaf157fd6e9 100644
>> --- a/fs/iomap/buffered-io.c
>> +++ b/fs/iomap/buffered-io.c
>> @@ -1062,24 +1062,16 @@ vm_fault_t iomap_page_mkwrite(struct vm_fault *vmf, const struct iomap_ops *ops)
>> struct page *page = vmf->page;
>> struct inode *inode = file_inode(vmf->vma->vm_file);
>> unsigned long length;
>> - loff_t offset, size;
>> + loff_t offset;
>> ssize_t ret;
>>
>> lock_page(page);
>> - size = i_size_read(inode);
>> - offset = page_offset(page);
>> - if (page->mapping != inode->i_mapping || offset > 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 (offset > size - PAGE_SIZE)
>> - length = offset_in_page(size);
>> - else
>> - length = PAGE_SIZE;
>> + length = ret;
>>
>> + offset = page_offset(page);
>> while (length > 0) {
>> ret = iomap_apply(inode, offset, length,
>> IOMAP_WRITE | IOMAP_FAULT, ops, page,
>> diff --git a/fs/ubifs/file.c b/fs/ubifs/file.c
>> index cd52585c8f4f..91f7a1f2db0d 100644
>> --- a/fs/ubifs/file.c
>> +++ b/fs/ubifs/file.c
>> @@ -1563,8 +1563,7 @@ static vm_fault_t ubifs_vm_page_mkwrite(struct vm_fault *vmf)
>> }
>>
>> lock_page(page);
>> - if (unlikely(page->mapping != inode->i_mapping ||
>> - page_offset(page) > i_size_read(inode))) {
>> + if (unlikely(page_mkwrite_check_truncate(page, inode) < 0)) {
>> /* Page got truncated out from underneath us */
>> goto sigbus;
>> }
>> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
>> index 37a4d9e32cd3..ccb14b6a16b5 100644
>> --- a/include/linux/pagemap.h
>> +++ b/include/linux/pagemap.h
>> @@ -636,4 +636,32 @@ static inline unsigned long dir_pages(struct inode *inode)
>> PAGE_SHIFT;
>> }
>>
>> +/**
>> + * page_mkwrite_check_truncate - check if page was truncated
>> + * @page: the page to check
>> + * @inode: the inode to check the page against
>> + *
>> + * Returns the number of bytes in the page up to EOF,
>> + * or -EFAULT if the page was truncated.
>> + */
>> +static inline int page_mkwrite_check_truncate(struct page *page,
>> + struct inode *inode)
>> +{
>> + loff_t size = i_size_read(inode);
>> + pgoff_t index = size >> PAGE_SHIFT;
>> + int offset = offset_in_page(size);
>> +
>> + if (page->mapping != inode->i_mapping)
>> + return -EFAULT;
>> +
>> + /* page is wholly inside EOF */
>> + if (page->index < index)
>> + return PAGE_SIZE;
>> + /* page is wholly past EOF */
>> + if (page->index > index || !offset)
>> + return -EFAULT;
>> + /* page is partially inside EOF */
>> + return offset;
>> +}
>> +
>> #endif /* _LINUX_PAGEMAP_H */
>> --
>> 2.20.1
>>
> .
>

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