[PATCH] readelf: While printing .debug_loc make sure that next_off doesn't overflow.

[PATCH] readelf: While printing .debug_loc make sure that next_off doesn't overflow.

[Mark Wielaard]

Found by the afl fuzzer. The next offset (after a locview) comes from a
DIE loclist attribute. This could be a bogus value so large it overflows
the buffer and makes us print past the end of buffer.

Signed-off-by: Mark Wielaard <mark@klomp.org>
---
 src/ChangeLog | 5 +++++
 src/readelf.c | 4 +++-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/src/ChangeLog b/src/ChangeLog
index 5f381cf..3d266e2 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,8 @@
+2018-06-16  Mark Wielaard  <mark@klomp.org>
+
+	* readelf.c (print_debug_loc_section): Make sure next_off doesn't
+	overflow d_buf.
+
 2018-06-13  Mark Wielaard  <mark@klomp.org>
 
 	* readelf.c (die_type_sign_bytes): New function.
diff --git a/src/readelf.c b/src/readelf.c
index 5e7061d..2e7378e 100644
--- a/src/readelf.c
+++ b/src/readelf.c
@@ -9310,7 +9310,9 @@ print_debug_loc_section (Dwfl_Module *dwflmod,
 						    listptr_idx);
 	  const unsigned char *locp = readp;
 	  const unsigned char *locendp;
-	  if (next_off == 0)
+	  if (next_off == 0
+	      || next_off > (size_t) (endp
+				      - (const unsigned char *) data->d_buf))
 	    locendp = endp;
 	  else
 	    locendp = (const unsigned char *) data->d_buf + next_off;
-- 
1.8.3.1

Re: [PATCH] readelf: While printing .debug_loc make sure that next_off doesn't overflow.

[Mark Wielaard]

On Wed, Jun 13, 2018 at 03:24:45PM +0200, Mark Wielaard wrote:
> Found by the afl fuzzer. The next offset (after a locview) comes from a
> DIE loclist attribute. This could be a bogus value so large it overflows
> the buffer and makes us print past the end of buffer.

Pushed to master.