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ASLR: fix stack randomization on 64-bit systems (CVE-2015-1593) 

svn path=/dists/sid/linux/; revision=22399
This commit is contained in:
Ben Hutchings 2015-02-17 05:25:56 +00:00
parent dfd470cb06
commit ef31d8f0b0
3 changed files with 100 additions and 0 deletions
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1
debian/changelog vendored
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@ -7,6 +7,7 @@ linux (3.16.7-ckt4-4) UNRELEASED; urgency=medium
* shm: add memfd.h to UAPI export list, so kdbus will build
* [x86] HPET force enable for e6xx based systems (Closes: #772951)
* vfs: read file_handle only once in handle_to_path (CVE-2015-1420)
* ASLR: fix stack randomization on 64-bit systems (CVE-2015-1593)
-- Ian Campbell <ijc@debian.org> Mon, 09 Feb 2015 06:17:31 +0000

98
debian/patches/bugfix/all/aslr-fix-stack-randomization-on-64-bit-systems.patch vendored Normal file
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@ -0,0 +1,98 @@
From: Hector Marco-Gisbert <hecmargi@upv.es>
Date: Sat, 14 Feb 2015 09:33:50 -0800
Subject: ASLR: fix stack randomization on 64-bit systems
Origin: http://article.gmane.org/gmane.linux.kernel/1888210
The issue is that the stack for processes is not properly randomized on 64 bit
architectures due to an integer overflow.
The affected function is randomize_stack_top() in file "fs/binfmt_elf.c":
static unsigned long randomize_stack_top(unsigned long stack_top)
{
unsigned int random_variable = 0;
if ((current->flags & PF_RANDOMIZE) &&
!(current->personality & ADDR_NO_RANDOMIZE)) {
random_variable = get_random_int() & STACK_RND_MASK;
random_variable <<= PAGE_SHIFT;
}
return PAGE_ALIGN(stack_top) + random_variable;
return PAGE_ALIGN(stack_top) - random_variable;
}
Note that, it declares the "random_variable" variable as "unsigned int". Since
the result of the shifting operation between STACK_RND_MASK (which is
0x3fffff on x86_64, 22 bits) and PAGE_SHIFT (which is 12 on x86_64):
random_variable <<= PAGE_SHIFT;
then the two leftmost bits are dropped when storing the result in the
"random_variable". This variable shall be at least 34 bits long to hold the
(22+12) result.
These two dropped bits have an impact on the entropy of process stack.
Concretely, the total stack entropy is reduced by four: from 2^28 to 2^30 (One
fourth of expected entropy).
This patch restores back the entropy by correcting the types involved in the
operations in the functions randomize_stack_top() and stack_maxrandom_size().
The successful fix can be tested with:
$ for i in `seq 1 10`; do cat /proc/self/maps | grep stack; done
7ffeda566000-7ffeda587000 rw-p 00000000 00:00 0 [stack]
7fff5a332000-7fff5a353000 rw-p 00000000 00:00 0 [stack]
7ffcdb7a1000-7ffcdb7c2000 rw-p 00000000 00:00 0 [stack]
7ffd5e2c4000-7ffd5e2e5000 rw-p 00000000 00:00 0 [stack]
...
Once corrected, the leading bytes should be between 7ffc and 7fff, rather
than always being 7fff.
CVE-2015-1593
Signed-off-by: Hector Marco-Gisbert <hecmargi@upv.es>
Signed-off-by: Ismael Ripoll <iripoll@upv.es>
[kees: rebase, fix 80 char, clean up commit message, add test example, cve]
Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: stable@vger.kernel.org
---
arch/x86/mm/mmap.c | 6 +++---
fs/binfmt_elf.c | 5 +++--
2 files changed, 6 insertions(+), 5 deletions(-)
--- a/arch/x86/mm/mmap.c
+++ b/arch/x86/mm/mmap.c
@@ -35,12 +35,12 @@ struct __read_mostly va_alignment va_ali
.flags = -1,
};
-static unsigned int stack_maxrandom_size(void)
+static unsigned long stack_maxrandom_size(void)
{
- unsigned int max = 0;
+ unsigned long max = 0;
if ((current->flags & PF_RANDOMIZE) &&
!(current->personality & ADDR_NO_RANDOMIZE)) {
- max = ((-1U) & STACK_RND_MASK) << PAGE_SHIFT;
+ max = ((-1UL) & STACK_RND_MASK) << PAGE_SHIFT;
}
return max;
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -554,11 +554,12 @@ out:
static unsigned long randomize_stack_top(unsigned long stack_top)
{
- unsigned int random_variable = 0;
+ unsigned long random_variable = 0;
if ((current->flags & PF_RANDOMIZE) &&
!(current->personality & ADDR_NO_RANDOMIZE)) {
- random_variable = get_random_int() & STACK_RND_MASK;
+ random_variable = (unsigned long) get_random_int();
+ random_variable &= STACK_RND_MASK;
random_variable <<= PAGE_SHIFT;
}
#ifdef CONFIG_STACK_GROWSUP

1
debian/patches/series vendored
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@ -504,3 +504,4 @@ bugfix/all/net-sctp-fix-slab-corruption-from-use-after-free-on-.patch
features/all/kdbus/shm-add-memfd.h-to-uapi-export-list.patch
bugfix/x86/x86-hpet-force-enable-for-e6xx-based-systems.patch
bugfix/all/vfs-read-file_handle-only-once-in-handle_to_path.patch
bugfix/all/aslr-fix-stack-randomization-on-64-bit-systems.patch