libdwfl: Make sure that ph_buffer_size has room for at least one phdr

dwfl_segment_report_module might otherwise try to handle half a phdr
taking the other half from after the buffer.

Signed-off-by: Mark Wielaard <mark@klomp.org>

2 files changed, 11 insertions, 1 deletions

diff --git a/libdwfl/ChangeLog b/libdwfl/ChangeLog
index d00ce702..38e2bdaa 100644
--- a/libdwfl/ChangeLog
+++ b/libdwfl/ChangeLog
@@ -1,5 +1,10 @@
 2021-12-08  Mark Wielaard  <mark@klomp.org>
 
+        * dwfl_segment_report_module.c (dwfl_segment_report_module): Make sure
+        that ph_buffer_size has room for at least one phdr.
+
+2021-12-08  Mark Wielaard  <mark@klomp.org>
+
         * dwfl_segment_report_module.c (dwfl_segment_report_module): Make
         sure the note len increases each iteration.
 
diff --git a/libdwfl/dwfl_segment_report_module.c b/libdwfl/dwfl_segment_report_module.c
index 89e05103..840d6f44 100644
--- a/libdwfl/dwfl_segment_report_module.c
+++ b/libdwfl/dwfl_segment_report_module.c
@@ -426,7 +426,12 @@ dwfl_segment_report_module (Dwfl *dwfl, int ndx, const char *name,
      buffer, otherwise it will be the size of the new buffer that
      could be read.  */
   if (ph_buffer_size != 0)
-    xlatefrom.d_size = ph_buffer_size;
+    {
+      phnum = ph_buffer_size / phentsize;
+      if (phnum == 0)
+        goto out;
+      xlatefrom.d_size = ph_buffer_size;
+    }
 
   xlatefrom.d_buf = ph_buffer;