xfs: assure zeroed memory buffers for certain kmem allocations

Guarantee zeroed memory buffers for cases where potential memory
leak to disk can occur. In these cases, kmem_alloc is used and
doesn't zero the buffer, opening the possibility of information
leakage to disk.

Use existing infrastucture (xfs_buf_allocate_memory) to obtain
the already zeroed buffer from kernel memory.

This solution avoids the performance issue that would occur if a
wholesale change to replace kmem_alloc with kmem_zalloc was done.

Signed-off-by: Bill O'Donnell <billodo@redhat.com>
[darrick: fix bitwise complaint about kmflag_mask]
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

fs/xfs/xfs_buf.c

@@ -345,6 +345,15 @@ xfs_buf_allocate_memory(
 	unsigned short		page_count, i;
 	xfs_off_t		start, end;
 	int			error;
+	xfs_km_flags_t		kmflag_mask = 0;
+
+	/*
+	 * assure zeroed buffer for non-read cases.
+	 */
+	if (!(flags & XBF_READ)) {
+		kmflag_mask |= KM_ZERO;
+		gfp_mask |= __GFP_ZERO;
+	}
 
 	/*
 	 * for buffers that are contained within a single page, just allocate
@@ -354,7 +363,8 @@ xfs_buf_allocate_memory(
 	size = BBTOB(bp->b_length);
 	if (size < PAGE_SIZE) {
 		int align_mask = xfs_buftarg_dma_alignment(bp->b_target);
-		bp->b_addr = kmem_alloc_io(size, align_mask, KM_NOFS);
+		bp->b_addr = kmem_alloc_io(size, align_mask,
+					   KM_NOFS | kmflag_mask);
 		if (!bp->b_addr) {
 			/* low memory - use alloc_page loop instead */
 			goto use_alloc_page;

fs/xfs/xfs_log.c

@@ -1443,7 +1443,7 @@ xlog_alloc_log(
 		prev_iclog = iclog;
 
 		iclog->ic_data = kmem_alloc_io(log->l_iclog_size, align_mask,
-						KM_MAYFAIL);
+						KM_MAYFAIL | KM_ZERO);
 		if (!iclog->ic_data)
 			goto out_free_iclog;
 #ifdef DEBUG

fs/xfs/xfs_log_recover.c

@@ -127,7 +127,7 @@ xlog_alloc_buffer(
 	if (nbblks > 1 && log->l_sectBBsize > 1)
 		nbblks += log->l_sectBBsize;
 	nbblks = round_up(nbblks, log->l_sectBBsize);
-	return kmem_alloc_io(BBTOB(nbblks), align_mask, KM_MAYFAIL);
+	return kmem_alloc_io(BBTOB(nbblks), align_mask, KM_MAYFAIL | KM_ZERO);
 }
 
 /*