Re: [PATCH hotfix 6.12 2/8] mm: unconditionally close VMAs on error

[Jann Horn <jannh@google.com>]

On Tue, Oct 22, 2024 at 10:41 PM Lorenzo Stoakes
<lorenzo.stoakes@oracle.com> wrote:
> Incorrect invocation of VMA callbacks when the VMA is no longer in a
> consistent state is bug prone and risky to perform.
>
> With regards to the important vm_ops->close() callback We have gone to
> great lengths to try to track whether or not we ought to close VMAs.
>
> Rather than doing so and risking making a mistake somewhere, instead
> unconditionally close and reset vma->vm_ops to an empty dummy operations
> set with a NULL .close operator.
>
> We introduce a new function to do so - vma_close() - and simplify existing
> vms logic which tracked whether we needed to close or not.
>
> This simplifies the logic, avoids incorrect double-calling of the .close()
> callback and allows us to update error paths to simply call vma_close()
> unconditionally - making VMA closure idempotent.
>
> Reported-by: Jann Horn <jannh@google.com>
> Fixes: deb0f6562884 ("mm/mmap: undo ->mmap() when arch_validate_flags() fails")
> Cc: stable <stable@kernel.org>
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>

Reviewed-by: Jann Horn <jannh@google.com>

[...]
> diff --git a/mm/vma.h b/mm/vma.h
> index 55457cb68200..75558b5e9c8c 100644
> --- a/mm/vma.h
> +++ b/mm/vma.h
> @@ -42,7 +42,6 @@ struct vma_munmap_struct {
>         int vma_count;                  /* Number of vmas that will be removed */
>         bool unlock;                    /* Unlock after the munmap */
>         bool clear_ptes;                /* If there are outstanding PTE to be cleared */
> -       bool closed_vm_ops;             /* call_mmap() was encountered, so vmas may be closed */
>         /* 1 byte hole */

nit: outdated comment, this hole is 2 bytes now



>         unsigned long nr_pages;         /* Number of pages being removed */
>         unsigned long locked_vm;        /* Number of locked pages */