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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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