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>

3 files changed, 13 insertions, 3 deletions

diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index 21c243622a79..0abba171aa89 100644
--- a/fs/xfs/xfs_buf.c
+++ b/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;
diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
index a2beee9f74da..641d07f30a27 100644
--- a/fs/xfs/xfs_log.c
+++ b/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
diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
index 508319039dce..c1a514ffff55 100644
--- a/fs/xfs/xfs_log_recover.c
+++ b/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);
 }
 
 /*