mirror of
https://github.com/archlinuxarm/PKGBUILDs.git
synced 2024-11-28 22:57:37 +00:00
113 lines
5 KiB
Diff
113 lines
5 KiB
Diff
From bc3293299bc4981e83b7f37f3615a6b9b27b6837 Mon Sep 17 00:00:00 2001
|
|
From: Markus Kuhn <Markus.Kuhn@cl.cam.ac.uk>
|
|
Date: Mon, 3 Aug 2020 21:09:39 +0100
|
|
Subject: [PATCH 13/15] new jbig.c limit s->maxmem: maximum decoded image size
|
|
(default: 2 GB)
|
|
|
|
this helps users to reduce denial-of-service risks, as in CVE-2017-9937
|
|
---
|
|
CHANGES | 9 +++++++++
|
|
libjbig/jbig.c | 5 +++++
|
|
libjbig/jbig.h | 2 ++
|
|
libjbig/jbig.txt | 39 ++++++++++++++++++++++++++++-----------
|
|
4 files changed, 44 insertions(+), 11 deletions(-)
|
|
|
|
diff --git a/libjbig/jbig.c b/libjbig/jbig.c
|
|
index fe54946..e9938e5 100644
|
|
--- a/libjbig/jbig.c
|
|
+++ b/libjbig/jbig.c
|
|
@@ -2051,6 +2051,7 @@ void jbg_dec_init(struct jbg_dec_state *s)
|
|
s->xmax = 4294967295UL;
|
|
s->ymax = 4294967295UL;
|
|
s->dmax = 256;
|
|
+ s->maxmem = 2000000000; /* no final image larger than 2 GB by default */
|
|
s->s = NULL;
|
|
|
|
return;
|
|
@@ -2640,6 +2641,10 @@ int jbg_dec_in(struct jbg_dec_state *s, unsigned char *data, size_t len,
|
|
return JBG_EIMPL | 5;
|
|
s->options = s->buffer[19];
|
|
|
|
+ /* will the final image require more bytes than permitted by s->maxmem? */
|
|
+ if (s->maxmem / s->planes / s->yd / jbg_ceil_half(s->xd, 3) == 0)
|
|
+ return JBG_ENOMEM; /* increase s->maxmem if needed */
|
|
+
|
|
/* calculate number of stripes that will be required */
|
|
s->stripes = jbg_stripes(s->l0, s->yd, s->d);
|
|
|
|
diff --git a/libjbig/jbig.h b/libjbig/jbig.h
|
|
index 81c1adc..2577399 100644
|
|
--- a/libjbig/jbig.h
|
|
+++ b/libjbig/jbig.h
|
|
@@ -181,6 +181,8 @@ struct jbg_dec_state {
|
|
unsigned long xmax, ymax; /* if possible abort before image gets *
|
|
* larger than this size */
|
|
int dmax; /* abort after this layer */
|
|
+ size_t maxmem; /* return JBG_ENOMEM if final image layer D
|
|
+ would require more than maxmem bytes */
|
|
};
|
|
|
|
|
|
diff --git a/libjbig/jbig.txt b/libjbig/jbig.txt
|
|
index 70ca464..4547b12 100644
|
|
--- a/libjbig/jbig.txt
|
|
+++ b/libjbig/jbig.txt
|
|
@@ -2,7 +2,7 @@
|
|
Using the JBIG-KIT library
|
|
--------------------------
|
|
|
|
-Markus Kuhn -- 2013-09-10
|
|
+Markus Kuhn -- 2020-08-03
|
|
|
|
|
|
This text explains how to use the functions provided by the JBIG-KIT
|
|
@@ -735,19 +735,36 @@ None of the above limitations can be exceeded by a JBIG data stream
|
|
that conforms to the ITU-T T.85 application profile for the use of
|
|
JBIG1 in fax machines.
|
|
|
|
-The current implementation of the jbig.c decoder does not impose any
|
|
-limits on the image size that it will process, as long as malloc() is
|
|
-able to allocate enough heap space for the resulting bitmaps. The only
|
|
-exception is that jbg_dec_in() will return "Input data stream uses
|
|
+The maximum image size that a BIE header (BIH) can indicate is X_D =
|
|
+2^32-1 pixels wide, Y_D = 2^32-1 lines high, with P = 255 bits per
|
|
+pixel. Such an image would, in uncompressed form, require about 588
|
|
+exabytes. Once jbg_dec_in() has received the 20-byte long BIH at the
|
|
+start of the BIE, it will call malloc() to allocate enough memory to
|
|
+hold the uncompressed image planes. Users may, therefore, want to
|
|
+defend their application against excessive image-size parameters in a
|
|
+received BIH, by checking X_D, Y_D, and P against appropriate safety
|
|
+limits before handing over the BIE header to jbg_dec_in(). BIE headers
|
|
+indicating too large images might be abused for denial of service
|
|
+attacks, to exhaust the memory of a system (e.g., CVE-2017-9937). To
|
|
+manage this risk, the jbig.c decoder will now, by default, return "Not
|
|
+enough memory available" (JBG_ENOMEM) if the resulting final image
|
|
+layer would occupy more than 2 gigabytes. Users can adjust this limit
|
|
+by changing sd->maxmem right after having called jbg_dec_init(&sd).
|
|
+The actual amount of memory allocated with malloc() calls during the
|
|
+decoding process is somewhat higher (at least 25%) than the limit set
|
|
+in sd->maxmem, as the decoder requires additional heap memory that
|
|
+depends on the image dimensions.
|
|
+
|
|
+The jbg_dec_in() function will return "Input data stream uses
|
|
unimplemented JBIG features" (JBG_EIMPL | 1) if Y_D equals 0xffffffff,
|
|
which is an extreme value commonly used to encode images according to
|
|
ITU-T T.85 where the height was unknown when the BIH was emitted.
|
|
-After jbg_dec_in() received the 20-byte long BIH at the start of the
|
|
-BIE, it will malloc() to allocate enough memory to hold the requested
|
|
-image planes and layers. If you want to defend your application
|
|
-against excessive image-size parameters in a received BIH, then do
|
|
-make sure that you check X_D, Y_D, and P against appropriate safety
|
|
-limits before handing over the BIH to jbg_dec_in().
|
|
+
|
|
+All malloc(), realloc() and free() functions called by jbig.c are
|
|
+wrapped by the functions checked_malloc(), checked_realloc() and
|
|
+checked_free(). These simply call abort() when memory allocation
|
|
+fails. Developpers of embedded systems may want to replace them with
|
|
+alternative forms of exception handling.
|
|
|
|
There are two more limitations of the current implementation of the
|
|
jbig.c decoder that might cause problems with processing JBIG data
|
|
--
|
|
2.45.0
|
|
|