[PATCH] readelf: Make sure print_form_data always consumes DW_FORM_strx[1234] data.

[Mark Wielaard]

Found by afl-fuzz. When printing DW_FORM_strx[1234] data eu-readelf didn't
increase readp which meant eu-readelf would keep printing the same line
dirs or files encoded with strx[1234] names. This meant that for insane
large dir or file counts eu-readelf would just keep printing endlessly
because we never reached and of the .debug_line buffer.

Signed-off-by: Mark Wielaard <m...@klomp.org>
---
 libdw/ChangeLog       |  4 ++++
 libdw/memory-access.h |  5 +++++
 src/ChangeLog         |  5 +++++
 src/readelf.c         | 12 ++++++------
 4 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/libdw/ChangeLog b/libdw/ChangeLog
index 78321654..6492c976 100644
--- a/libdw/ChangeLog
+++ b/libdw/ChangeLog
@@ -1,3 +1,7 @@
+2018-06-12  Mark Wielaard  <m...@klomp.org>
+
+       * memory-access.h (read_3ubyte_unaligned_inc): New define.
+
 2018-06-12  Mark Wielaard  <m...@klomp.org>
 
        * libdw.h (__libdw_dieabbrev): Set die->abbrev to DWARF_END_ABBREV
diff --git a/libdw/memory-access.h b/libdw/memory-access.h
index 22918cb9..a39ad6d2 100644
--- a/libdw/memory-access.h
+++ b/libdw/memory-access.h
@@ -362,6 +362,11 @@ read_3ubyte_unaligned (Dwarf *dbg, const unsigned char *p)
 }
 
 
+#define read_3ubyte_unaligned_inc(Dbg, Addr) \
+  ({ uint32_t t_ = read_2ubyte_unaligned (Dbg, Addr);                        \
+     Addr = (__typeof (Addr)) (((uintptr_t) (Addr)) + 3);                    \
+     t_; })
+
 #define read_addr_unaligned_inc(Nbytes, Dbg, Addr)                     \
   (assert ((Nbytes) == 4 || (Nbytes) == 8),                            \
     ((Nbytes) == 4 ? read_4ubyte_unaligned_inc (Dbg, Addr)             \
diff --git a/src/ChangeLog b/src/ChangeLog
index fd45405f..fbbb9acb 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,8 @@
+2018-06-12  Mark Wielaard  <m...@klomp.org>
+
+       * print_form_data): Don't increase strreadp after use.  Do
+       increase readp for DW_FORM_strx[1234].
+
 2018-06-11  Mark Wielaard  <m...@klomp.org>
 
        * readelf.c (print_form_data): Don't reuse readp and readendp when
diff --git a/src/readelf.c b/src/readelf.c
index f1858971..17d91735 100644
--- a/src/readelf.c
+++ b/src/readelf.c
@@ -7994,9 +7994,9 @@ print_form_data (Dwarf *dbg, int form, const unsigned 
char *readp,
            {
              Dwarf_Off idx;
              if (offset_len == 8)
-               idx = read_8ubyte_unaligned_inc (dbg, strreadp);
+               idx = read_8ubyte_unaligned (dbg, strreadp);
              else
-               idx = read_4ubyte_unaligned_inc (dbg, strreadp);
+               idx = read_4ubyte_unaligned (dbg, strreadp);
 
              data = dbg->sectiondata[IDX_debug_str];
              if (data == NULL || idx >= data->d_size
@@ -8013,25 +8013,25 @@ print_form_data (Dwarf *dbg, int form, const unsigned 
char *readp,
     case DW_FORM_strx1:
       if (readendp - readp < 1)
        goto invalid_data;
-      val = *readp;
+      val = *readp++;
       goto strx_val;
 
     case DW_FORM_strx2:
       if (readendp - readp < 2)
        goto invalid_data;
-      val = read_2ubyte_unaligned (dbg, readp);
+      val = read_2ubyte_unaligned_inc (dbg, readp);
       goto strx_val;
 
     case DW_FORM_strx3:
       if (readendp - readp < 3)
        goto invalid_data;
-      val = read_3ubyte_unaligned (dbg, readp);
+      val = read_3ubyte_unaligned_inc (dbg, readp);
       goto strx_val;
 
     case DW_FORM_strx4:
       if (readendp - readp < 4)
        goto invalid_data;
-      val = read_4ubyte_unaligned (dbg, readp);
+      val = read_4ubyte_unaligned_inc (dbg, readp);
       goto strx_val;
 
     default:
-- 
2.17.0