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