2020-03-23 13:31:47

by Alexander Gordeev

Subject: [PATCH 0/2] mm/mmap: check mapping limits more strictly

From: Alexander Gordeev <[email protected]>

This series is against v5.6-rc7

Alexander Gordeev (2):
mm/mmap.c: add more sanity checks to get_unmapped_area()
mm/mmap.c: do not allow mappings outside of allowed limits

mm/mmap.c | 29 +++++++++++++++++------------
1 file changed, 17 insertions(+), 12 deletions(-)

--
2.23.0

2020-03-23 13:31:58

by Alexander Gordeev

Subject: [PATCH 2/2] mm/mmap.c: do not allow mappings outside of allowed limits

From: Alexander Gordeev <[email protected]>

It is possible to request a fixed mapping address below
mmap_min_addr and succeed. This update adds early checks
of mmap_min_addr and mmap_end boundaries and fixes the
above issue.

Signed-off-by: Alexander Gordeev <[email protected]>
---
mm/mmap.c | 24 ++++++++++++++----------
1 file changed, 14 insertions(+), 10 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index a0fcb5ca0e06..bd673a01b1d0 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -59,6 +59,14 @@
#define arch_mmap_check(addr, len, flags) (0)
#endif

+#ifndef arch_get_mmap_end
+#define arch_get_mmap_end(addr) (TASK_SIZE)
+#endif
+
+#ifndef arch_get_mmap_base
+#define arch_get_mmap_base(addr, base) (base)
+#endif
+
#ifdef CONFIG_HAVE_ARCH_MMAP_RND_BITS
const int mmap_rnd_bits_min = CONFIG_ARCH_MMAP_RND_BITS_MIN;
const int mmap_rnd_bits_max = CONFIG_ARCH_MMAP_RND_BITS_MAX;
@@ -1366,6 +1374,7 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
unsigned long pgoff, unsigned long *populate,
struct list_head *uf)
{
+ const unsigned long mmap_end = arch_get_mmap_end(addr);
struct mm_struct *mm = current->mm;
int pkey = 0;

@@ -1388,8 +1397,12 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
if (flags & MAP_FIXED_NOREPLACE)
flags |= MAP_FIXED;

- if (!(flags & MAP_FIXED))
+ if (flags & MAP_FIXED) {
+ if ((addr < mmap_min_addr) || (addr > mmap_end))
+ return -ENOMEM;
+ } else {
addr = round_hint_to_min(addr);
+ }

/* Careful about overflows.. */
len = PAGE_ALIGN(len);
@@ -2050,15 +2063,6 @@ unsigned long unmapped_area_topdown(struct vm_unmapped_area_info *info)
return gap_end;
}

-
-#ifndef arch_get_mmap_end
-#define arch_get_mmap_end(addr) (TASK_SIZE)
-#endif
-
-#ifndef arch_get_mmap_base
-#define arch_get_mmap_base(addr, base) (base)
-#endif
-
/* Get an address range which is currently unmapped.
* For shmat() with addr=0.
*
--
2.23.0

2020-04-21 03:00:38

by Andrew Morton

Subject: Re: [PATCH 2/2] mm/mmap.c: do not allow mappings outside of allowed limits

On Mon, 23 Mar 2020 14:29:29 +0100 [email protected] wrote:

> It is possible to request a fixed mapping address below
> mmap_min_addr and succeed. This update adds early checks
> of mmap_min_addr and mmap_end boundaries and fixes the
> above issue.

Does this solve any known problems? If not, what is the motivation for
the change?

2020-04-21 05:35:50

by Alexander Gordeev

Subject: Re: [PATCH 2/2] mm/mmap.c: do not allow mappings outside of allowed limits

On Mon, Apr 20, 2020 at 07:59:03PM -0700, Andrew Morton wrote:
> On Mon, 23 Mar 2020 14:29:29 +0100 [email protected] wrote:
>
> > It is possible to request a fixed mapping address below
> > mmap_min_addr and succeed. This update adds early checks
> > of mmap_min_addr and mmap_end boundaries and fixes the
> > above issue.
>
> Does this solve any known problems? If not, what is the motivation for
> the change?

One can set a lowest possible address in /proc/sys/vm/mmap_min_addr
and mmap below that bound nevertheless. Apart from it is wrong I am
not aware of any existing issue.

Thanks!