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    Subject[PATCH v2 10/11] mm: SLAB hardened usercopy support
    Date
    Under CONFIG_HARDENED_USERCOPY, this adds object size checking to the
    SLAB allocator to catch any copies that may span objects.

    Based on code from PaX and grsecurity.

    Signed-off-by: Kees Cook <keescook@chromium.org>
    ---
    init/Kconfig | 1 +
    mm/slab.c | 30 ++++++++++++++++++++++++++++++
    2 files changed, 31 insertions(+)

    diff --git a/init/Kconfig b/init/Kconfig
    index f755a602d4a1..798c2020ee7c 100644
    --- a/init/Kconfig
    +++ b/init/Kconfig
    @@ -1757,6 +1757,7 @@ choice

    config SLAB
    bool "SLAB"
    + select HAVE_HARDENED_USERCOPY_ALLOCATOR
    help
    The regular slab allocator that is established and known to work
    well in all environments. It organizes cache hot objects in
    diff --git a/mm/slab.c b/mm/slab.c
    index cc8bbc1e6bc9..5e2d5f349aca 100644
    --- a/mm/slab.c
    +++ b/mm/slab.c
    @@ -4477,6 +4477,36 @@ static int __init slab_proc_init(void)
    module_init(slab_proc_init);
    #endif

    +#ifdef CONFIG_HARDENED_USERCOPY
    +/*
    + * Rejects objects that are incorrectly sized.
    + *
    + * Returns NULL if check passes, otherwise const char * to name of cache
    + * to indicate an error.
    + */
    +const char *__check_heap_object(const void *ptr, unsigned long n,
    + struct page *page)
    +{
    + struct kmem_cache *cachep;
    + unsigned int objnr;
    + unsigned long offset;
    +
    + /* Find and validate object. */
    + cachep = page->slab_cache;
    + objnr = obj_to_index(cachep, page, (void *)ptr);
    + BUG_ON(objnr >= cachep->num);
    +
    + /* Find offset within object. */
    + offset = ptr - index_to_obj(cachep, page, objnr) - obj_offset(cachep);
    +
    + /* Allow address range falling entirely within object size. */
    + if (offset <= cachep->object_size && n <= cachep->object_size - offset)
    + return NULL;
    +
    + return cachep->name;
    +}
    +#endif /* CONFIG_HARDENED_USERCOPY */
    +
    /**
    * ksize - get the actual amount of memory allocated for a given object
    * @objp: Pointer to the object
    --
    2.7.4
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