* [PATCH] readelf: Fix bounds check in print_form_data.
@ 2018-06-11 0:18 Mark Wielaard
2018-06-11 15:52 ` Mark Wielaard
0 siblings, 1 reply; 2+ messages in thread
From: Mark Wielaard @ 2018-06-11 0:18 UTC (permalink / raw)
To: elfutils-devel; +Cc: Mark Wielaard
The afl fuzzer found that we did a wrong check in print_form_data when
comparing the remaining bytes in the buffer to an (unsigned) value read.
We were casting the value to ptrdiff_t which is a signed value and so
might turn a really big unsigned value into a negative number. Since we
know the difference between readendp and readp is zero or greater, we
should cast the pointer difference to size_t (and unsigned type) instead
before comparing with the unsigned value.
Signed-off-by: Mark Wielaard <mark@klomp.org>
---
src/ChangeLog | 5 +++++
src/readelf.c | 14 +++++++-------
2 files changed, 12 insertions(+), 7 deletions(-)
diff --git a/src/ChangeLog b/src/ChangeLog
index 8ebb5fb..6484b9a 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,8 @@
+2018-06-10 Mark Wielaard <mark@klomp.org>
+
+ * readelf.c (print_form_data): Don't cast value to ptrdiff_t, cast
+ ptrdiff_t to size_t.
+
2018-06-08 Mark Wielaard <mark@klomp.org>
* readelf.c (print_debug_rnglists_section): Calculate max_entries
diff --git a/src/readelf.c b/src/readelf.c
index bbaaf96..fbda6c1 100644
--- a/src/readelf.c
+++ b/src/readelf.c
@@ -7880,7 +7880,7 @@ print_form_data (Dwarf *dbg, int form, const unsigned char *readp,
if (readendp - readp < 1)
goto invalid_data;
get_uleb128 (val, readp, readendp);
- if (readendp - readp < (ptrdiff_t) val)
+ if ((size_t) (readendp - readp) < val)
goto invalid_data;
print_bytes (val, readp);
readp += val;
@@ -7890,7 +7890,7 @@ print_form_data (Dwarf *dbg, int form, const unsigned char *readp,
if (readendp - readp < 1)
goto invalid_data;
val = *readp++;
- if (readendp - readp < (ptrdiff_t) val)
+ if ((size_t) (readendp - readp) < val)
goto invalid_data;
print_bytes (val, readp);
readp += val;
@@ -7900,7 +7900,7 @@ print_form_data (Dwarf *dbg, int form, const unsigned char *readp,
if (readendp - readp < 2)
goto invalid_data;
val = read_2ubyte_unaligned_inc (dbg, readp);
- if (readendp - readp < (ptrdiff_t) val)
+ if ((size_t) (readendp - readp) < val)
goto invalid_data;
print_bytes (val, readp);
readp += val;
@@ -7910,7 +7910,7 @@ print_form_data (Dwarf *dbg, int form, const unsigned char *readp,
if (readendp - readp < 2)
goto invalid_data;
val = read_4ubyte_unaligned_inc (dbg, readp);
- if (readendp - readp < (ptrdiff_t) val)
+ if ((size_t) (readendp - readp) < val)
goto invalid_data;
print_bytes (val, readp);
readp += val;
@@ -7941,7 +7941,7 @@ print_form_data (Dwarf *dbg, int form, const unsigned char *readp,
case DW_FORM_strp:
case DW_FORM_line_strp:
case DW_FORM_strp_sup:
- if (readendp - readp < (ptrdiff_t) offset_len)
+ if ((size_t) (readendp - readp) < offset_len)
goto invalid_data;
if (offset_len == 8)
val = read_8ubyte_unaligned_inc (dbg, readp);
@@ -7965,7 +7965,7 @@ print_form_data (Dwarf *dbg, int form, const unsigned char *readp,
break;
case DW_FORM_sec_offset:
- if (readendp - readp < (ptrdiff_t) offset_len)
+ if ((size_t) (readendp - readp) < offset_len)
goto invalid_data;
if (offset_len == 8)
val = read_8ubyte_unaligned_inc (dbg, readp);
@@ -7988,7 +7988,7 @@ print_form_data (Dwarf *dbg, int form, const unsigned char *readp,
{
readp = data->d_buf + str_offsets_base + val;
readendp = data->d_buf + data->d_size;
- if (readendp - readp < (ptrdiff_t) offset_len)
+ if ((size_t) (readendp - readp) < offset_len)
str = "???";
else
{
--
1.8.3.1
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [PATCH] readelf: Fix bounds check in print_form_data.
2018-06-11 0:18 [PATCH] readelf: Fix bounds check in print_form_data Mark Wielaard
@ 2018-06-11 15:52 ` Mark Wielaard
0 siblings, 0 replies; 2+ messages in thread
From: Mark Wielaard @ 2018-06-11 15:52 UTC (permalink / raw)
To: elfutils-devel
On Mon, 2018-06-11 at 02:18 +0200, Mark Wielaard wrote:
> The afl fuzzer found that we did a wrong check in print_form_data when
> comparing the remaining bytes in the buffer to an (unsigned) value read.
> We were casting the value to ptrdiff_t which is a signed value and so
> might turn a really big unsigned value into a negative number. Since we
> know the difference between readendp and readp is zero or greater, we
> should cast the pointer difference to size_t (and unsigned type) instead
> before comparing with the unsigned value.
Pushed to master
^ permalink raw reply [flat|nested] 2+ messages in thread
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2018-06-11 15:52 ` Mark Wielaard
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