diff options
Diffstat (limited to 'gnu/packages/patches')
| -rw-r--r-- | gnu/packages/patches/fontconfig-CVE-2016-5384.patch | 170 |
1 files changed, 170 insertions, 0 deletions
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 0000000000..617d5afbaf --- /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 + |