[PATCH] libdwfl: add check for elf_memory return value

[vvvvvv@google.com]

From: Aleksei Vetrov <vvvvvv@google.com>

elf_memory call in __libdw_open_elf_memory can return NULL. It was not
checked and led to the null pointer dereference.

Signed-off-by: Aleksei Vetrov <vvvvvv@google.com>
---
 libdwfl/open.c                     | 4 ++++
 tests/dwfl-report-offline-memory.c | 9 +++++++--
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/libdwfl/open.c b/libdwfl/open.c
index b97ff016..d0f357ed 100644
--- a/libdwfl/open.c
+++ b/libdwfl/open.c
@@ -211,6 +211,10 @@ __libdw_open_elf_memory (char *data, size_t size, Elf **elfp, bool archive_ok)
      won't work.  */
   int fd = -1;
   *elfp = elf_memory (data, size);
+  if (unlikely(*elfp == NULL))
+    {
+      return DWFL_E_LIBELF;
+    }
   /* Allow using this ELF as reference for subsequent elf_begin calls.  */
   (*elfp)->cmd = ELF_C_READ_MMAP_PRIVATE;
   return libdw_open_elf (&fd, elfp, false, archive_ok, true, false, true);
diff --git a/tests/dwfl-report-offline-memory.c b/tests/dwfl-report-offline-memory.c
index e6cb0a51..b3b4d9bd 100644
--- a/tests/dwfl-report-offline-memory.c
+++ b/tests/dwfl-report-offline-memory.c
@@ -77,8 +77,13 @@ main (int argc, char **argv)
   Dwfl *dwfl = dwfl_begin (&offline_callbacks);
   assert (dwfl != NULL);
 
-  Dwfl_Module *mod =
-      dwfl_report_offline_memory (dwfl, argv[1], argv[1], data, size);
+  Dwfl_Module *mod;
+
+  /* Check error handling by suppling zero data */
+  mod = dwfl_report_offline_memory(dwfl, argv[1], argv[1], NULL, 0);
+  assert(mod == NULL);
+
+  mod = dwfl_report_offline_memory(dwfl, argv[1], argv[1], data, size);
   assert (mod != NULL);
   dwfl_report_end (dwfl, NULL, NULL);
 
-- 
2.39.1.405.gd4c25cc71f-goog