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    SubjectRe: [PATCH] VMCI: Annotate struct vmci_handle_arr with __counted_by
    On Sat, Oct 07, 2023 at 04:32:34PM +0200, Christophe JAILLET wrote:
    > Prepare for the coming implementation by GCC and Clang of the __counted_by
    > attribute. Flexible array members annotated with __counted_by can have
    > their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
    > (for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
    > functions).
    >
    > Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
    > ---
    > This patch is part of a work done in parallel of what is currently worked
    > on by Kees Cook.
    >
    > My patches are only related to corner cases that do NOT match the
    > semantic of his Coccinelle script[1].
    >
    > In this case, something similar to struct_size() is implemented in
    > handle_arr_calc_size().

    I think this should likely lose VMCI_HANDLE_ARRAY_HEADER_SIZE entirely
    and the helper to use sizeof() and struct_size() directly, but probably
    as a separate patch.

    >
    > Note that I'm slightly unsure on how things will behave in regards to the
    > krealloc() in vmci_handle_arr_append_entry().

    It looks correct to me:

    new_array = krealloc(array, new_size, GFP_ATOMIC);
    ...
    new_array->capacity += capacity_bump;

    i.e. "capacity" is adjusted up before accessing any "entries".

    >
    > [1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci
    > ---
    > drivers/misc/vmw_vmci/vmci_handle_array.h | 2 +-
    > 1 file changed, 1 insertion(+), 1 deletion(-)
    >
    > diff --git a/drivers/misc/vmw_vmci/vmci_handle_array.h b/drivers/misc/vmw_vmci/vmci_handle_array.h
    > index 96193f85be5b..b0e6b1956014 100644
    > --- a/drivers/misc/vmw_vmci/vmci_handle_array.h
    > +++ b/drivers/misc/vmw_vmci/vmci_handle_array.h
    > @@ -17,7 +17,7 @@ struct vmci_handle_arr {
    > u32 max_capacity;
    > u32 size;
    > u32 pad;
    > - struct vmci_handle entries[];
    > + struct vmci_handle entries[] __counted_by(capacity);
    > };
    >
    > #define VMCI_HANDLE_ARRAY_HEADER_SIZE \
    > --
    > 2.34.1
    >

    Reviewed-by: Kees Cook <keescook@chromium.org>


    --
    Kees Cook

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