* [PATCH 1/1] gnu: fontconfig: Fix CVE-2016-5384.
2016-08-08 22:59 [PATCH 0/1] fontconfig: CVE-2016-5384 Leo Famulari
@ 2016-08-08 22:59 ` Leo Famulari
2016-08-08 23:17 ` [PATCH 0/1] fontconfig: CVE-2016-5384 Mark H Weaver
1 sibling, 0 replies; 4+ messages in thread
From: Leo Famulari @ 2016-08-08 22:59 UTC (permalink / raw)
To: guix-devel
* gnu/packages/fontutils.scm (fontconfig)[replacement]: New field.
(fontconfig/fixed): New variable.
* gnu/packages/patches/fontconfig-CVE-2016-5384.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.
---
gnu/local.mk | 1 +
gnu/packages/fontutils.scm | 8 +
.../patches/fontconfig-CVE-2016-5384.patch | 170 +++++++++++++++++++++
3 files changed, 179 insertions(+)
create mode 100644 gnu/packages/patches/fontconfig-CVE-2016-5384.patch
diff --git a/gnu/local.mk b/gnu/local.mk
index c0671e8..7630b2d 100644
--- a/gnu/local.mk
+++ b/gnu/local.mk
@@ -505,6 +505,7 @@ dist_patch_DATA = \
%D%/packages/patches/flint-ldconfig.patch \
%D%/packages/patches/fltk-shared-lib-defines.patch \
%D%/packages/patches/fltk-xfont-on-demand.patch \
+ %D%/packages/patches/fontconfig-CVE-2016-5384.patch \
%D%/packages/patches/fontforge-svg-modtime.patch \
%D%/packages/patches/fossil-test-fixes.patch \
%D%/packages/patches/freeimage-CVE-2015-0852.patch \
diff --git a/gnu/packages/fontutils.scm b/gnu/packages/fontutils.scm
index 9ddbaec..4867164 100644
--- a/gnu/packages/fontutils.scm
+++ b/gnu/packages/fontutils.scm
@@ -223,6 +223,7 @@ fonts to/from the WOFF2 format.")
(define-public fontconfig
(package
(name "fontconfig")
+ (replacement fontconfig/fixed)
(version "2.11.94")
(source (origin
(method url-fetch)
@@ -275,6 +276,13 @@ high quality, anti-aliased and subpixel rendered text on a display.")
"See COPYING in the distribution."))
(home-page "http://www.freedesktop.org/wiki/Software/fontconfig")))
+(define fontconfig/fixed
+ (package
+ (inherit fontconfig)
+ (source (origin
+ (inherit (package-source fontconfig))
+ (patches (search-patches "fontconfig-CVE-2016-5384.patch"))))))
+
(define-public t1lib
(package
(name "t1lib")
diff --git a/gnu/packages/patches/fontconfig-CVE-2016-5384.patch b/gnu/packages/patches/fontconfig-CVE-2016-5384.patch
new file mode 100644
index 0000000..617d5af
--- /dev/null
+++ b/gnu/packages/patches/fontconfig-CVE-2016-5384.patch
@@ -0,0 +1,170 @@
+Fix CVE-2016-5384 (double-free resulting in arbitrary code execution):
+
+<https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-5384>
+
+Copied from upstream code repository:
+
+<https://cgit.freedesktop.org/fontconfig/commit/?id=7a4a5bd7897d216f0794ca9dbce0a4a5c9d14940>
+
+From 7a4a5bd7897d216f0794ca9dbce0a4a5c9d14940 Mon Sep 17 00:00:00 2001
+From: Tobias Stoeckmann <tobias@stoeckmann.org>
+Date: Sat, 25 Jun 2016 19:18:53 +0200
+Subject: Properly validate offsets in cache files.
+
+The cache files are insufficiently validated. Even though the magic
+number at the beginning of the file as well as time stamps are checked,
+it is not verified if contained offsets are in legal ranges or are
+even pointers.
+
+The lack of validation allows an attacker to trigger arbitrary free()
+calls, which in turn allows double free attacks and therefore arbitrary
+code execution. Due to the conversion from offsets into pointers through
+macros, this even allows to circumvent ASLR protections.
+
+This attack vector allows privilege escalation when used with setuid
+binaries like fbterm. A user can create ~/.fonts or any other
+system-defined user-private font directory, run fc-cache and adjust
+cache files in ~/.cache/fontconfig. The execution of setuid binaries will
+scan these files and therefore are prone to attacks.
+
+If it's not about code execution, an endless loop can be created by
+letting linked lists become circular linked lists.
+
+This patch verifies that:
+
+- The file is not larger than the maximum addressable space, which
+ basically only affects 32 bit systems. This allows out of boundary
+ access into unallocated memory.
+- Offsets are always positive or zero
+- Offsets do not point outside file boundaries
+- No pointers are allowed in cache files, every "pointer or offset"
+ field must be an offset or NULL
+- Iterating linked lists must not take longer than the amount of elements
+ specified. A violation of this rule can break a possible endless loop.
+
+If one or more of these points are violated, the cache is recreated.
+This is current behaviour.
+
+Even though this patch fixes many issues, the use of mmap() shall be
+forbidden in setuid binaries. It is impossible to guarantee with these
+checks that a malicious user does not change cache files after
+verification. This should be handled in a different patch.
+
+Signed-off-by: Tobias Stoeckmann <tobias@stoeckmann.org>
+
+diff --git a/src/fccache.c b/src/fccache.c
+index 71e8f03..02ec301 100644
+--- a/src/fccache.c
++++ b/src/fccache.c
+@@ -27,6 +27,7 @@
+ #include <fcntl.h>
+ #include <dirent.h>
+ #include <string.h>
++#include <limits.h>
+ #include <sys/types.h>
+ #include <sys/stat.h>
+ #include <assert.h>
+@@ -587,6 +588,82 @@ FcCacheTimeValid (FcConfig *config, FcCache *cache, struct stat *dir_stat)
+ return cache->checksum == (int) dir_stat->st_mtime && fnano;
+ }
+
++static FcBool
++FcCacheOffsetsValid (FcCache *cache)
++{
++ char *base = (char *)cache;
++ char *end = base + cache->size;
++ intptr_t *dirs;
++ FcFontSet *fs;
++ int i, j;
++
++ if (cache->dir < 0 || cache->dir > cache->size - sizeof (intptr_t) ||
++ memchr (base + cache->dir, '\0', cache->size - cache->dir) == NULL)
++ return FcFalse;
++
++ if (cache->dirs < 0 || cache->dirs >= cache->size ||
++ cache->dirs_count < 0 ||
++ cache->dirs_count > (cache->size - cache->dirs) / sizeof (intptr_t))
++ return FcFalse;
++
++ dirs = FcCacheDirs (cache);
++ if (dirs)
++ {
++ for (i = 0; i < cache->dirs_count; i++)
++ {
++ FcChar8 *dir;
++
++ if (dirs[i] < 0 ||
++ dirs[i] > end - (char *) dirs - sizeof (intptr_t))
++ return FcFalse;
++
++ dir = FcOffsetToPtr (dirs, dirs[i], FcChar8);
++ if (memchr (dir, '\0', end - (char *) dir) == NULL)
++ return FcFalse;
++ }
++ }
++
++ if (cache->set < 0 || cache->set > cache->size - sizeof (FcFontSet))
++ return FcFalse;
++
++ fs = FcCacheSet (cache);
++ if (fs)
++ {
++ if (fs->nfont > (end - (char *) fs) / sizeof (FcPattern))
++ return FcFalse;
++
++ if (fs->fonts != 0 && !FcIsEncodedOffset(fs->fonts))
++ return FcFalse;
++
++ for (i = 0; i < fs->nfont; i++)
++ {
++ FcPattern *font = FcFontSetFont (fs, i);
++ FcPatternElt *e;
++ FcValueListPtr l;
++
++ if ((char *) font < base ||
++ (char *) font > end - sizeof (FcFontSet) ||
++ font->elts_offset < 0 ||
++ font->elts_offset > end - (char *) font ||
++ font->num > (end - (char *) font - font->elts_offset) / sizeof (FcPatternElt))
++ return FcFalse;
++
++
++ e = FcPatternElts(font);
++ if (e->values != 0 && !FcIsEncodedOffset(e->values))
++ return FcFalse;
++
++ for (j = font->num, l = FcPatternEltValues(e); j >= 0 && l; j--, l = FcValueListNext(l))
++ if (l->next != NULL && !FcIsEncodedOffset(l->next))
++ break;
++ if (j < 0)
++ return FcFalse;
++ }
++ }
++
++ return FcTrue;
++}
++
+ /*
+ * Map a cache file into memory
+ */
+@@ -596,7 +673,8 @@ FcDirCacheMapFd (FcConfig *config, int fd, struct stat *fd_stat, struct stat *di
+ FcCache *cache;
+ FcBool allocated = FcFalse;
+
+- if (fd_stat->st_size < (int) sizeof (FcCache))
++ if (fd_stat->st_size > INTPTR_MAX ||
++ fd_stat->st_size < (int) sizeof (FcCache))
+ return NULL;
+ cache = FcCacheFindByStat (fd_stat);
+ if (cache)
+@@ -652,6 +730,7 @@ FcDirCacheMapFd (FcConfig *config, int fd, struct stat *fd_stat, struct stat *di
+ if (cache->magic != FC_CACHE_MAGIC_MMAP ||
+ cache->version < FC_CACHE_VERSION_NUMBER ||
+ cache->size != (intptr_t) fd_stat->st_size ||
++ !FcCacheOffsetsValid (cache) ||
+ !FcCacheTimeValid (config, cache, dir_stat) ||
+ !FcCacheInsert (cache, fd_stat))
+ {
+--
+cgit v0.10.2
+
--
2.9.2
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