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Subject[34-longterm 184/209] install_special_mapping skips security_file_mmap check.
Date
From: Tavis Ormandy <taviso@cmpxchg8b.com>

=====================================================================
| This is a commit scheduled for the next v2.6.34 longterm release. |
| If you see a problem with using this for longterm, please comment.|
=====================================================================
commit 462e635e5b73ba9a4c03913b77138cd57ce4b050 upstream.

The install_special_mapping routine (used, for example, to setup the
vdso) skips the security check before insert_vm_struct, allowing a local
attacker to bypass the mmap_min_addr security restriction by limiting
the available pages for special mappings.

bprm_mm_init() also skips the check, and although I don't think this can
be used to bypass any restrictions, I don't see any reason not to have
the security check.

$ uname -m
x86_64
$ cat /proc/sys/vm/mmap_min_addr
65536
$ cat install_special_mapping.s
section .bss
resb BSS_SIZE
section .text
global _start
_start:
mov eax, __NR_pause
int 0x80
$ nasm -D__NR_pause=29 -DBSS_SIZE=0xfffed000 -f elf -o install_special_mapping.o install_special_mapping.s
$ ld -m elf_i386 -Ttext=0x10000 -Tbss=0x11000 -o install_special_mapping install_special_mapping.o
$ ./install_special_mapping &
[1] 14303
$ cat /proc/14303/maps
0000f000-00010000 r-xp 00000000 00:00 0 [vdso]
00010000-00011000 r-xp 00001000 00:19 2453665 /home/taviso/install_special_mapping
00011000-ffffe000 rwxp 00000000 00:00 0 [stack]
It's worth noting that Red Hat are shipping with mmap_min_addr set to
4096.

Signed-off-by: Tavis Ormandy <taviso@google.com>
Acked-by: Kees Cook <kees@ubuntu.com>
Acked-by: Robert Swiecki <swiecki@google.com>
[ Changed to not drop the error code - akpm ]
Reviewed-by: James Morris <jmorris@namei.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
---
fs/exec.c | 5 +++++
mm/mmap.c | 16 ++++++++++++----
2 files changed, 17 insertions(+), 4 deletions(-)
diff --git a/fs/exec.c b/fs/exec.c
index 8d4912f..5bc2413 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -268,6 +268,11 @@ static int __bprm_mm_init(struct linux_binprm *bprm)
vma->vm_flags = VM_STACK_FLAGS;
vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
INIT_LIST_HEAD(&vma->anon_vma_chain);
+
+ err = security_file_mmap(NULL, 0, 0, 0, vma->vm_start, 1);
+ if (err)
+ goto err;
+
err = insert_vm_struct(mm, vma);
if (err)
goto err;
diff --git a/mm/mmap.c b/mm/mmap.c
index 10cb197..b42b469 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2443,6 +2443,7 @@ int install_special_mapping(struct mm_struct *mm,
unsigned long addr, unsigned long len,
unsigned long vm_flags, struct page **pages)
{
+ int ret;
struct vm_area_struct *vma;

vma = kmem_cache_zalloc(vm_area_cachep, GFP_KERNEL);
@@ -2460,16 +2461,23 @@ int install_special_mapping(struct mm_struct *mm,
vma->vm_ops = &special_mapping_vmops;
vma->vm_private_data = pages;

- if (unlikely(insert_vm_struct(mm, vma))) {
- kmem_cache_free(vm_area_cachep, vma);
- return -ENOMEM;
- }
+ ret = security_file_mmap(NULL, 0, 0, 0, vma->vm_start, 1);
+ if (ret)
+ goto out;
+
+ ret = insert_vm_struct(mm, vma);
+ if (ret)
+ goto out;

mm->total_vm += len >> PAGE_SHIFT;

perf_event_mmap(vma);

return 0;
+
+out:
+ kmem_cache_free(vm_area_cachep, vma);
+ return ret;
}

static DEFINE_MUTEX(mm_all_locks_mutex);
--
1.7.4.4


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