| From 462e635e5b73ba9a4c03913b77138cd57ce4b050 Mon Sep 17 00:00:00 2001 |
| From: Tavis Ormandy <taviso@cmpxchg8b.com> |
| Date: Thu, 9 Dec 2010 15:29:42 +0100 |
| Subject: install_special_mapping skips security_file_mmap check. |
| |
| From: Tavis Ormandy <taviso@cmpxchg8b.com> |
| |
| 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: Greg Kroah-Hartman <gregkh@suse.de> |
| |
| --- |
| fs/exec.c | 5 +++++ |
| mm/mmap.c | 16 ++++++++++++---- |
| 2 files changed, 17 insertions(+), 4 deletions(-) |
| |
| --- a/fs/exec.c |
| +++ b/fs/exec.c |
| @@ -246,6 +246,11 @@ static int __bprm_mm_init(struct linux_b |
| vma->vm_start = vma->vm_end - PAGE_SIZE; |
| 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) |
| goto err; |
| --- a/mm/mmap.c |
| +++ b/mm/mmap.c |
| @@ -2348,6 +2348,7 @@ int install_special_mapping(struct mm_st |
| 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); |
| @@ -2364,16 +2365,23 @@ int install_special_mapping(struct mm_st |
| 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); |