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    Subject[PATCH 3.11 21/70] mm: make fixup_user_fault() check the vma access rights too
    Date
    3.11.10.10 -stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Linus Torvalds <torvalds@linux-foundation.org>

    commit 1b17844b29ae042576bea588164f2f1e9590a8bc upstream.

    fixup_user_fault() is used by the futex code when the direct user access
    fails, and the futex code wants it to either map in the page in a usable
    form or return an error. It relied on handle_mm_fault() to map the
    page, and correctly checked the error return from that, but while that
    does map the page, it doesn't actually guarantee that the page will be
    mapped with sufficient permissions to be then accessed.

    So do the appropriate tests of the vma access rights by hand.

    [ Side note: arguably handle_mm_fault() could just do that itself, but
    we have traditionally done it in the caller, because some callers -
    notably get_user_pages() - have been able to access pages even when
    they are mapped with PROT_NONE. Maybe we should re-visit that design
    decision, but in the meantime this is the minimal patch. ]

    Found by Dave Jones running his trinity tool.

    Reported-by: Dave Jones <davej@redhat.com>
    Acked-by: Hugh Dickins <hughd@google.com>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
    ---
    mm/memory.c | 5 +++++
    1 file changed, 5 insertions(+)

    diff --git a/mm/memory.c b/mm/memory.c
    index 168a090..3d64ffa 100644
    --- a/mm/memory.c
    +++ b/mm/memory.c
    @@ -1940,12 +1940,17 @@ int fixup_user_fault(struct task_struct *tsk, struct mm_struct *mm,
    unsigned long address, unsigned int fault_flags)
    {
    struct vm_area_struct *vma;
    + vm_flags_t vm_flags;
    int ret;

    vma = find_extend_vma(mm, address);
    if (!vma || address < vma->vm_start)
    return -EFAULT;

    + vm_flags = (fault_flags & FAULT_FLAG_WRITE) ? VM_WRITE : VM_READ;
    + if (!(vm_flags & vma->vm_flags))
    + return -EFAULT;
    +
    ret = handle_mm_fault(mm, vma, address, fault_flags);
    if (ret & VM_FAULT_ERROR) {
    if (ret & VM_FAULT_OOM)
    --
    1.9.1


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