Re: [PATCH 2/3 -v2] mmap: round mmap hint address above mmap_min_addr

James Morris
2007-11-27T01:05:44Z

On Mon, 26 Nov 2007, Eric Paris wrote:

> If mmap_min_addr is set and a process attempts to mmap (not fixed) with
> a non-null hint address less than mmap_min_addr the mapping will fail
> the security checks. Since this is just a hint address this patch will
> round such a hint address above mmap_min_addr.
>
> gcj was found to try to be very frugal with vm usage and give hint
> addresses in the 8k-32k range. Without this patch all such programs
> failed and with the patch they happily get a higher address.
>
> This patch is wrappad in CONFIG_SECURITY since mmap_min_addr doesn't
> exist without it and there would be no security check possible no matter
> what. So we should not bother compiling in this rounding if it is just a
> waste of time.
>
> Signed-off-by: Eric Paris <eparis@redhat.com>

Applied to
git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/selinux-2.6.git#for-akpm

>
> ---
>
> include/linux/mm.h | 16 ++++++++++++++++
> mm/mmap.c | 3 +++
> mm/nommu.c | 3 +++
> 3 files changed, 22 insertions(+), 0 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 520238c..1b7b95c 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -12,6 +12,7 @@
> #include <linux/prio_tree.h>
> #include <linux/debug_locks.h>
> #include <linux/mm_types.h>
> +#include <linux/security.h>
>
> struct mempolicy;
> struct anon_vma;
> @@ -513,6 +514,21 @@ static inline void set_page_links(struct page *page, enum zone_type zone,
> }
>
> /*
> + * If a hint addr is less than mmap_min_addr change hint to be as
> + * low as possible but still greater than mmap_min_addr
> + */
> +static inline unsigned long round_hint_to_min(unsigned long hint)
> +{
> +#ifdef CONFIG_SECURITY
> + hint &= PAGE_MASK;
> + if (((void *)hint != NULL) &&
> + (hint < mmap_min_addr))
> + return PAGE_ALIGN(mmap_min_addr);
> +#endif
> + return hint;
> +}
> +
> +/*
> * Some inline functions in vmstat.h depend on page_zone()
> */
> #include <linux/vmstat.h>
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 938313c..f4cfc6a 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -912,6 +912,9 @@ unsigned long do_mmap_pgoff(struct file * file, unsigned long addr,
> if (!len)
> return -EINVAL;
>
> + if (!(flags & MAP_FIXED))
> + addr = round_hint_to_min(addr);
> +
> error = arch_mmap_check(addr, len, flags);
> if (error)
> return error;
> diff --git a/mm/nommu.c b/mm/nommu.c
> index 35622c5..b989cb9 100644
> --- a/mm/nommu.c
> +++ b/mm/nommu.c
> @@ -829,6 +829,9 @@ unsigned long do_mmap_pgoff(struct file *file,
> void *result;
> int ret;
>
> + if (!(flags & MAP_FIXED))
> + addr = round_hint_to_min(addr);
> +
> /* decide whether we should attempt the mapping, and if so what sort of
> * mapping */
> ret = validate_mmap_request(file, addr, len, prot, flags, pgoff,
>
>

--
James Morris
<jmorris@namei.org>