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.
Introduce a xfs_buf_flag, _XBF_KMZ, to indicate a request for a zeroed
buffer, and 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@xxxxxxxxxx>
---
fs/xfs/xfs_buf.c | 8 ++++++--
fs/xfs/xfs_buf.h | 4 +++-
2 files changed, 9 insertions(+), 3 deletions(-)
diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index 120ef99d09e8..916a3f782950 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -345,16 +345,19 @@ xfs_buf_allocate_memory(
unsigned short page_count, i;
xfs_off_t start, end;
int error;
+ uint kmflag_mask = 0;
/*
* for buffers that are contained within a single page, just allocate
* the memory from the heap - there's no need for the complexity of
* page arrays to keep allocation down to order 0.
*/
+ if (flags & _XBF_KMZ)
+ kmflag_mask |= KM_ZERO;
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;
@@ -391,7 +394,7 @@ xfs_buf_allocate_memory(
struct page *page;
uint retries = 0;
retry:
- page = alloc_page(gfp_mask);
+ page = alloc_page(gfp_mask | kmflag_mask);
if (unlikely(page == NULL)) {
if (flags & XBF_READ_AHEAD) {
bp->b_page_count = i;
@@ -683,6 +686,7 @@ xfs_buf_get_map(
struct xfs_buf *new_bp;
int error = 0;
+ flags |= _XBF_KMZ;
error = xfs_buf_find(target, map, nmaps, flags, NULL, &bp);
switch (error) {
diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h
index f6ce17d8d848..416ff588240a 100644
--- a/fs/xfs/xfs_buf.h
+++ b/fs/xfs/xfs_buf.h
@@ -38,6 +38,7 @@
#define _XBF_PAGES (1 << 20)/* backed by refcounted pages */
#define _XBF_KMEM (1 << 21)/* backed by heap memory */
#define _XBF_DELWRI_Q (1 << 22)/* buffer on a delwri queue */
+#define _XBF_KMZ (1 << 23)/* zeroed buffer required */
typedef unsigned int xfs_buf_flags_t;
@@ -54,7 +55,8 @@ typedef unsigned int xfs_buf_flags_t;
{ XBF_UNMAPPED, "UNMAPPED" }, /* ditto */\
{ _XBF_PAGES, "PAGES" }, \
{ _XBF_KMEM, "KMEM" }, \
- { _XBF_DELWRI_Q, "DELWRI_Q" }
+ { _XBF_DELWRI_Q, "DELWRI_Q" }, \
+ { _XBF_KMZ, "KMEM_Z" }
/*
--
2.21.0
