Commit 0b578f35 authored by Chandan Rajendra's avatar Chandan Rajendra Committed by Eric Biggers
Browse files

ext4: decrypt only the needed blocks in ext4_block_write_begin() 



In ext4_block_write_begin(), only decrypt the blocks that actually need
to be decrypted (up to two blocks which intersect the boundaries of the
region that will be written to), rather than assuming blocksize ==
PAGE_SIZE and decrypting the whole page.

This is in preparation for allowing encryption on ext4 filesystems with
blocksize != PAGE_SIZE.

Signed-off-by: default avatarChandan Rajendra <chandan@linux.ibm.com>
(EB: rebase onto previous changes, improve the commit message,
 and move the check for encrypted inode)
Signed-off-by: default avatarEric Biggers <ebiggers@google.com>
parent 7e0785fc

fs/ext4/inode.c

+18 −11
Original line number Diff line number Diff line
@@ -1164,8 +1164,9 @@ static int ext4_block_write_begin(struct page *page, loff_t pos, unsigned len, 
	int err = 0;

	unsigned blocksize = inode->i_sb->s_blocksize;

	unsigned bbits;

	struct buffer_head *bh, *head, *wait[2], **wait_bh = wait;

	bool decrypt = false;

	struct buffer_head *bh, *head, *wait[2];

	int nr_wait = 0;

	int i;



	BUG_ON(!PageLocked(page));

	BUG_ON(from > PAGE_SIZE);
@@ -1217,24 +1218,30 @@ static int ext4_block_write_begin(struct page *page, loff_t pos, unsigned len, 
		    !buffer_unwritten(bh) &&

		    (block_start < from || block_end > to)) {

			ll_rw_block(REQ_OP_READ, 0, 1, &bh);

			*wait_bh++ = bh;

			decrypt = IS_ENCRYPTED(inode) && S_ISREG(inode->i_mode);

			wait[nr_wait++] = bh;

		}

	}

	/*

	 * If we issued read requests, let them complete.

	 */

	while (wait_bh > wait) {

		wait_on_buffer(*--wait_bh);

		if (!buffer_uptodate(*wait_bh))

	for (i = 0; i < nr_wait; i++) {

		wait_on_buffer(wait[i]);

		if (!buffer_uptodate(wait[i]))

			err = -EIO;

	}

	if (unlikely(err)) {

		page_zero_new_buffers(page, from, to);

	} else if (decrypt) {

		err = fscrypt_decrypt_pagecache_blocks(page, PAGE_SIZE, 0);

		if (err)

			clear_buffer_uptodate(*wait_bh);

	} else if (IS_ENCRYPTED(inode) && S_ISREG(inode->i_mode)) {

		for (i = 0; i < nr_wait; i++) {

			int err2;



			err2 = fscrypt_decrypt_pagecache_blocks(page, blocksize,

								bh_offset(wait[i]));

			if (err2) {

				clear_buffer_uptodate(wait[i]);

				err = err2;

			}

		}

	}



	return err;

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