[Qemu-devel] [PATCH 1/2] qcow2: Do not overflow when writing an L1 sector

[Max Reitz <mreitz@redhat.com>]

While writing an L1 table sector, qcow2_write_l1_entry() copies the
respective range from s->l1_table to the local "buf" array. The size of
s->l1_table does not have to be a multiple of L1_ENTRIES_PER_SECTOR;
thus, limit the index which is used for copying all entries to the L1
size.

Cc: qemu-stable@nongnu.org
Signed-off-by: Max Reitz <mreitz@redhat.com>
---
 block/qcow2-cluster.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index f7dd8c0..4d888c7 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -164,12 +164,14 @@ static int l2_load(BlockDriverState *bs, uint64_t l2_offset,
 int qcow2_write_l1_entry(BlockDriverState *bs, int l1_index)
 {
     BDRVQcowState *s = bs->opaque;
-    uint64_t buf[L1_ENTRIES_PER_SECTOR];
+    uint64_t buf[L1_ENTRIES_PER_SECTOR] = { 0 };
     int l1_start_index;
     int i, ret;
 
     l1_start_index = l1_index & ~(L1_ENTRIES_PER_SECTOR - 1);
-    for (i = 0; i < L1_ENTRIES_PER_SECTOR; i++) {
+    for (i = 0; i < L1_ENTRIES_PER_SECTOR && l1_start_index + i < s->l1_size;
+         i++)
+    {
         buf[i] = cpu_to_be64(s->l1_table[l1_start_index + i]);
     }
 
-- 
2.1.2