[Xen-devel] [PATCH v7 for-4.9 2/5] hvm/dmop: Make copy_buf_{from, to}_guest for a buffer not big enough an error.

[<jennifer.herbert@xxxxxxxxxx>]

From: Jennifer Herbert <jennifer.herbert@xxxxxxxxxx>

This makes copying to or from a buf that isn't big enough an error.
If the buffer isnt big enough, trying to carry on regardless
can only cause trouble later on.

Signed-off-by: Jennifer Herbert <Jennifer.Herbert@xxxxxxxxxx>
--
CC: Paul Durrant <paul.durrant@xxxxxxxxxx>
CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Julien Grall <julien.grall@xxxxxxx>
---
This patch takes the behaviour change part of patch the previouse
[patch 2/4].
---
 xen/arch/x86/hvm/dm.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/xen/arch/x86/hvm/dm.c b/xen/arch/x86/hvm/dm.c
index e583e41..63aa46c 100644
--- a/xen/arch/x86/hvm/dm.c
+++ b/xen/arch/x86/hvm/dm.c
@@ -36,30 +36,32 @@ static bool copy_buf_from_guest(const xen_dm_op_buf_t 
bufs[],
                                 unsigned int nr_bufs, void *dst,
                                 unsigned int idx, size_t dst_size)
 {
-    size_t size;
+    size_t buf_bytes;
 
     if ( idx >= nr_bufs )
         return false;
 
-    memset(dst, 0, dst_size);
-
-    size = min_t(size_t, dst_size, bufs[idx].size);
+    buf_bytes = bufs[idx].size;
+    if ( dst_size > buf_bytes )
+        return false;
 
-    return !copy_from_guest(dst, bufs[idx].h, size);
+    return !copy_from_guest(dst, bufs[idx].h, buf_bytes);
 }
 
 static bool copy_buf_to_guest(const xen_dm_op_buf_t bufs[],
                               unsigned int nr_bufs, unsigned int idx,
                               const void *src, size_t src_size)
 {
-    size_t size;
+    size_t buf_bytes;
 
     if ( idx >= nr_bufs )
         return false;
 
-    size = min_t(size_t, bufs[idx].size, src_size);
+    buf_bytes = bufs[idx].size;
+    if ( src_size > buf_bytes )
+        return false;
 
-    return !copy_to_guest(bufs[idx].h, src, size);
+    return !copy_to_guest(bufs[idx].h, src, buf_bytes);
 }
 
 static int track_dirty_vram(struct domain *d, xen_pfn_t first_pfn,
-- 
2.1.4


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