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_ZERO, 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>
---
v2: zeroed buffer not required for XBF_READ case. Correct placement
and rename the XBF_ZERO flag.
fs/xfs/xfs_buf.c | 9 +++++++--
fs/xfs/xfs_buf.h | 2 ++
fs/xfs/xfs_trans_buf.c | 2 ++
3 files changed, 11 insertions(+), 2 deletions(-)
diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index 120ef99d09e8..0d96efff451e 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -345,6 +345,10 @@ xfs_buf_allocate_memory(
unsigned short page_count, i;
xfs_off_t start, end;
int error;
+ uint kmflag_mask = 0;
+
+ if ((flags & XBF_ZERO) && !(flags & XBF_READ))
+ kmflag_mask |= KM_ZERO;
/*
* for buffers that are contained within a single page, just allocate
@@ -354,7 +358,8 @@ 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;
@@ -391,7 +396,7 @@ 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;
diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h
index f6ce17d8d848..dccdd653c9dc 100644
--- a/fs/xfs/xfs_buf.h
+++ b/fs/xfs/xfs_buf.h
@@ -33,6 +33,7 @@
/* flags used only as arguments to access routines */
#define XBF_TRYLOCK (1 << 16)/* lock requested, but do not wait */
#define XBF_UNMAPPED (1 << 17)/* do not map the buffer */
+#define XBF_ZERO (1 << 18)/* zeroed buffer required */
/* flags used only internally */
#define _XBF_PAGES (1 << 20)/* backed by refcounted pages */
@@ -52,6 +53,7 @@ typedef unsigned int xfs_buf_flags_t;
{ XBF_WRITE_FAIL, "WRITE_FAIL" }, \
{ XBF_TRYLOCK, "TRYLOCK" }, /* should never be set */\
{ XBF_UNMAPPED, "UNMAPPED" }, /* ditto */\
+ { XBF_ZERO, "KMEM_ZERO" }, \
{ _XBF_PAGES, "PAGES" }, \
{ _XBF_KMEM, "KMEM" }, \
{ _XBF_DELWRI_Q, "DELWRI_Q" }
diff --git a/fs/xfs/xfs_trans_buf.c b/fs/xfs/xfs_trans_buf.c
index b5b3a78ef31c..087d413c1490 100644
--- a/fs/xfs/xfs_trans_buf.c
+++ b/fs/xfs/xfs_trans_buf.c
@@ -123,6 +123,8 @@ xfs_trans_get_buf_map(
xfs_buf_t *bp;
struct xfs_buf_log_item *bip;
+ flags |= XBF_ZERO;
+
if (!tp)
return xfs_buf_get_map(target, map, nmaps, flags);
--
2.21.0
