Revised [CVE-2010-4346 Hardy] install_special_mapping skips security_file_mmap check. CVE-2010-4346

[Brad Figg]

On 03/10/2011 10:50 AM, Steve Conklin wrote:
> From: Tavis Ormandy<taviso at cmpxchg8b.com>
>
> BugLink: http://bugs.launchpad.net/bugs/731971
>
> CVE-2010-4346
>
> 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 at google.com>
> Acked-by: Kees Cook<kees at ubuntu.com>
> Acked-by: Robert Swiecki<swiecki at google.com>
> [ Changed to not drop the error code - akpm ]
> Reviewed-by: James Morris<jmorris at namei.org>
> Signed-off-by: Linus Torvalds<torvalds at linux-foundation.org>
> backported from upstream commit 462e635e5b73ba9a4c03913b77138cd57ce4b050
> Signed-off-by: Steve Conklin<sconklin at canonical.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 1340386..5788ef8 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -235,6 +235,11 @@ 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);
> +
> +	err = security_file_mmap(NULL, 0, 0, 0, vma->vm_start, 1);
> +	if (err)
> +		goto err;
> +
>   	err = insert_vm_struct(mm, vma);
>   	if (err) {
>   		up_write(&mm->mmap_sem);
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 6f9b289..974ecc0 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -2210,6 +2210,7 @@ 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);
> @@ -2226,12 +2227,19 @@ 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;
>
>   	return 0;
> +
> +out:
> +	kmem_cache_free(vm_area_cachep, vma);
> +	return ret;
>   }

Acked-by: Brad Figg <brad.figg at canonical.com>

-- 
Brad Figg brad.figg at canonical.com http://www.canonical.com