[Qemu-devel] [PATCH] qcow2: avoid memcpy(dst, NULL, len)

[Stefan Hajnoczi <stefanha@redhat.com>]

Section "7.1.4 Use of library functions" in the C99 standard says:

  If an argument to a function has an invalid value (such as [...]
  a null pointer [...]) [...] the behavior is undefined.

Additionally the "searching and sorting" functions are specified as
requiring valid pointer values as described in 7.1.4.

This patch fixes the following static analyzer errors:

  block/qcow2.c:1807:41: runtime error: null pointer passed as argument 2, which is declared to never be null
  block/qcow2-cluster.c:86:26: runtime error: null pointer passed as argument 2, which is declared to never be null

Reported-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 block/qcow2-cluster.c | 4 +++-
 block/qcow2.c         | 5 ++++-
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index f941835..ab0dcdc 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -83,7 +83,9 @@ int qcow2_grow_l1_table(BlockDriverState *bs, uint64_t min_size,
     }
     memset(new_l1_table, 0, align_offset(new_l1_size2, 512));
 
-    memcpy(new_l1_table, s->l1_table, s->l1_size * sizeof(uint64_t));
+    if (s->l1_table) {
+        memcpy(new_l1_table, s->l1_table, s->l1_size * sizeof(uint64_t));
+    }
 
     /* write new table (align to cluster) */
     BLKDBG_EVENT(bs->file, BLKDBG_L1_GROW_ALLOC_TABLE);
diff --git a/block/qcow2.c b/block/qcow2.c
index c079aa8..758a997 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -1804,7 +1804,10 @@ static size_t header_ext_add(char *buf, uint32_t magic, const void *s,
         .magic  = cpu_to_be32(magic),
         .len    = cpu_to_be32(len),
     };
-    memcpy(buf + sizeof(QCowExtension), s, len);
+
+    if (s) {
+        memcpy(buf + sizeof(QCowExtension), s, len);
+    }
 
     return ext_len;
 }
-- 
2.7.4