Messages in this thread Patch in this message | | | Date | Mon, 07 Feb 2011 00:23:15 +0100 | From | Willy Tarreau <> | Subject | [PATCH 23/23] install_special_mapping skips security_file_mmap check. |
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2.6.27.58-stable review patch. If anyone has any objections, please let us know.
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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> Signed-off-by: Willy Tarreau <w@1wt.eu>
--- fs/exec.c | 5 +++++ mm/mmap.c | 16 ++++++++++++---- 2 files changed, 17 insertions(+), 4 deletions(-)
Index: longterm-2.6.27/fs/exec.c =================================================================== --- longterm-2.6.27.orig/fs/exec.c 2011-01-29 11:22:46.000000000 +0100 +++ longterm-2.6.27/fs/exec.c 2011-01-29 15:36:13.479064083 +0100 @@ -257,6 +257,11 @@ 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); Index: longterm-2.6.27/mm/mmap.c =================================================================== --- longterm-2.6.27.orig/mm/mmap.c 2011-01-29 11:22:46.000000000 +0100 +++ longterm-2.6.27/mm/mmap.c 2011-01-29 15:38:47.368066702 +0100 @@ -2253,6 +2253,7 @@ 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); @@ -2269,14 +2270,21 @@ 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; } static DEFINE_MUTEX(mm_all_locks_mutex);
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