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fs: Fix page_mkwrite off-by-one errors 

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 iomap.

NOTE from Darrick: The original patch fixed a number of filesystems, but
then there were merge conflicts with the f2fs for-next tree; a
subsequent re-submission of the patch had different btrfs changes with
no explanation; and Christoph complained that each per-fs fix should be
a separate patch.  In my view that's too much risk to take on, so I
decided to drop all the hunks except for iomap, since I've actually QA'd
XFS.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
[darrick: drop everything but the iomap parts]
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
This commit is contained in:
Andreas Gruenbacher 2020-01-06 08:58:23 -08:00 committed by Darrick J. Wong
parent fd6988496e
commit 243145bc43
2 changed files with 33 additions and 13 deletions
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18
fs/iomap/buffered-io.c
View File

@ -1077,24 +1077,16 @@ 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,

28
include/linux/pagemap.h
View File

@ -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 */