GFS2: Fix writing to non-page aligned gfs2_quota structures

This is the upstream fix for this bug. This patch differs
from the RHEL5 fix (Red Hat bz #555754) which simply writes to the 8-byte
value field of the quota. In upstream quota code, we're
required to write the entire quota (88 bytes) which can be split
across a page boundary. We check for such quotas, and read/write
the two parts from/to the corresponding pages holding these parts.

With this patch, I don't see the bug anymore using the reproducer
in Red Hat bz 555754. I successfully ran a couple of simple tests/mounts/
umounts and it doesn't seem like this patch breaks anything else.

Signed-off-by: Abhi Das <adas@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

fs/gfs2/quota.c

@@ -637,15 +637,40 @@ static int gfs2_adjust_quota(struct gfs2_inode *ip, loff_t loc,
 	unsigned blocksize, iblock, pos;
 	struct buffer_head *bh, *dibh;
 	struct page *page;
-	void *kaddr;
-	struct gfs2_quota *qp;
-	s64 value;
-	int err = -EIO;
+	void *kaddr, *ptr;
+	struct gfs2_quota q, *qp;
+	int err, nbytes;
 	u64 size;
 
 	if (gfs2_is_stuffed(ip))
 		gfs2_unstuff_dinode(ip, NULL);
-	
+
+	memset(&q, 0, sizeof(struct gfs2_quota));
+	err = gfs2_internal_read(ip, NULL, (char *)&q, &loc, sizeof(q));
+	if (err < 0)
+		return err;
+
+	err = -EIO;
+	qp = &q;
+	qp->qu_value = be64_to_cpu(qp->qu_value);
+	qp->qu_value += change;
+	qp->qu_value = cpu_to_be64(qp->qu_value);
+	qd->qd_qb.qb_value = qp->qu_value;
+	if (fdq) {
+		if (fdq->d_fieldmask & FS_DQ_BSOFT) {
+			qp->qu_warn = cpu_to_be64(fdq->d_blk_softlimit);
+			qd->qd_qb.qb_warn = qp->qu_warn;
+		}
+		if (fdq->d_fieldmask & FS_DQ_BHARD) {
+			qp->qu_limit = cpu_to_be64(fdq->d_blk_hardlimit);
+			qd->qd_qb.qb_limit = qp->qu_limit;
+		}
+	}
+
+	/* Write the quota into the quota file on disk */
+	ptr = qp;
+	nbytes = sizeof(struct gfs2_quota);
+get_a_page:
 	page = grab_cache_page(mapping, index);
 	if (!page)
 		return -ENOMEM;
@@ -667,7 +692,12 @@ static int gfs2_adjust_quota(struct gfs2_inode *ip, loff_t loc,
 	if (!buffer_mapped(bh)) {
 		gfs2_block_map(inode, iblock, bh, 1);
 		if (!buffer_mapped(bh))
-			goto unlock;
+			goto unlock_out;
+		/* If it's a newly allocated disk block for quota, zero it */
+		if (buffer_new(bh)) {
+			memset(bh->b_data, 0, bh->b_size);
+			set_buffer_uptodate(bh);
+		}
 	}
 
 	if (PageUptodate(page))
@@ -677,32 +707,34 @@ static int gfs2_adjust_quota(struct gfs2_inode *ip, loff_t loc,
 		ll_rw_block(READ_META, 1, &bh);
 		wait_on_buffer(bh);
 		if (!buffer_uptodate(bh))
-			goto unlock;
+			goto unlock_out;
 	}
 
 	gfs2_trans_add_bh(ip->i_gl, bh, 0);
 
 	kaddr = kmap_atomic(page, KM_USER0);
-	qp = kaddr + offset;
-	value = (s64)be64_to_cpu(qp->qu_value) + change;
-	qp->qu_value = cpu_to_be64(value);
-	qd->qd_qb.qb_value = qp->qu_value;
-	if (fdq) {
-		if (fdq->d_fieldmask & FS_DQ_BSOFT) {
-			qp->qu_warn = cpu_to_be64(fdq->d_blk_softlimit);
-			qd->qd_qb.qb_warn = qp->qu_warn;
-		}
-		if (fdq->d_fieldmask & FS_DQ_BHARD) {
-			qp->qu_limit = cpu_to_be64(fdq->d_blk_hardlimit);
-			qd->qd_qb.qb_limit = qp->qu_limit;
-		}
-	}
+	if (offset + sizeof(struct gfs2_quota) > PAGE_CACHE_SIZE)
+		nbytes = PAGE_CACHE_SIZE - offset;
+	memcpy(kaddr + offset, ptr, nbytes);
 	flush_dcache_page(page);
 	kunmap_atomic(kaddr, KM_USER0);
+	unlock_page(page);
+	page_cache_release(page);
 
+	/* If quota straddles page boundary, we need to update the rest of the
+	 * quota at the beginning of the next page */
+	if (offset != 0) { /* first page, offset is closer to PAGE_CACHE_SIZE */
+		ptr = ptr + nbytes;
+		nbytes = sizeof(struct gfs2_quota) - nbytes;
+		offset = 0;
+		index++;
+		goto get_a_page;
+	}
+
+	/* Update the disk inode timestamp and size (if extended) */
 	err = gfs2_meta_inode_buffer(ip, &dibh);
 	if (err)
-		goto unlock;
+		goto out;
 
 	size = loc + sizeof(struct gfs2_quota);
 	if (size > inode->i_size) {
@@ -715,7 +747,9 @@ static int gfs2_adjust_quota(struct gfs2_inode *ip, loff_t loc,
 	brelse(dibh);
 	mark_inode_dirty(inode);
 
-unlock:
+out:
+	return err;
+unlock_out:
 	unlock_page(page);
 	page_cache_release(page);
 	return err;
@@ -779,8 +813,10 @@ static int do_sync(unsigned int num_qd, struct gfs2_quota_data **qda)
 	 * rgrp since it won't be allocated during the transaction
 	 */
 	al->al_requested = 1;
-	/* +1 in the end for block requested above for unstuffing */
-	blocks = num_qd * data_blocks + RES_DINODE + num_qd + 1;
+	/* +3 in the end for unstuffing block, inode size update block
+	 * and another block in case quota straddles page boundary and 
+	 * two blocks need to be updated instead of 1 */
+	blocks = num_qd * data_blocks + RES_DINODE + num_qd + 3;
 
 	if (nalloc)
 		al->al_requested += nalloc * (data_blocks + ind_blocks);